Diodes ZXLD1370 User Manual

A

f

Description

The ZXLD1370 is an LED driver controller IC for driving external

MOSFETs to drive high current LEDs. It is a multi-topology controller

enabling it to efficiently control the current through series connected

LEDs. The multi-topology enables it to operate in buck, boost and

buck-boost configurations.

The 60V capability coupled with its multi-topology capability enables it

to be used in a wide range of applications and drive in excess of

15 LEDs in series.

The ZXLD1370 is a modified hysteretic controller using a patent

pending control scheme providing high output current accuracy in all

three modes of operation. High accuracy dimming is achieved

through DC control and high frequency PWM control.

The ZXLD1370 uses two pins for fault diagnosis. A flag output

highlights a fault, while the multi-level status pin gives further

information on the exact fault.

Product Line o

Diodes Incorporated

ZXLD1370

60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST

LED DRIVER-CONTROLLER WITH AEC-Q100

Pin Assignments

TSSOP-16EP

Features

• 0.5% Typical Output Current Accuracy

• 6V to 60V Operating Voltage Range

• LED Driver Supports Buck, Boost and Buck-Boost

Configurations

• Wide Dynamic Range Dimming

• 20:1 DC Dimming

• 1000:1 Dimming Range at 500Hz

• Up to 1MHz Switching

• High Temperature Control of LED Current Using TADJ

• Available in Automotive Grade with AEC-Q100 and TS16949

Certification

• Available in “Green” Molding Compound (No Br, Sb) with Lead

Free Finish/ RoHS Compliant

 Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)

 Halogen and Antimony Free. “Green” Device (Note 3)

Notes: 1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.

2. See http://www.diodes.com for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green" and Lead-free.

3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

1 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Typical Applications Circuit

Product Line o

Diodes Incorporated

ZXLD1370

Buck-Boost Diagram Utilizing Thermistor and TADJ

Functional Block Diagram

Curve Showing LED Current vs. T

LED

ZXLD1370

Document number: DS32165 Rev. 5 - 2

2 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Pin Descriptions

Pin Name Pin

ADJ 1 I

REF 2 O Internal 1.25V reference voltage output.

TADJ 3 I

SHP 4 I/O

STATUS 5 O

SGND 6 P Signal ground (Connect to 0V)

PGND 7 P Power ground - Connect to 0V and pin 8 to maximize copper area

N/C 8 -

N/C 9

GATE 10 O Gate drive output to external NMOS transistor – connect to pin 9

V

AUX

VIN

ISM 13 I

FLAG 14 O

PWM 15 I

GI 16 I

EP PAD P Exposed paddle. Connect to 0V plane for electrical and thermal management

Note: 4. Type refers to whether or not pin is an Input, Output, Input/Output or power supply pin.

11 P

12 P

ZXLD1370

Document number: DS32165 Rev. 5 - 2

Type

(Note 4)

Function

Adjust input (for dc output current control).
Connect to REF to set 100% output current.

Drive with dc voltage (125mV<V
The ADJ pin has an internal clamp that limits the internal
failsafe should they get overdriven.

Temperature Adjust input for LED thermal current control.
Connect thermistor/resistor network to this pin to reduce output current above a preset temperature

threshold.

Connect to REF to disable thermal compensation function. (See section on thermal control.)

Shaping capacitor for feedback control loop.
Connect 100pF ±20% capacitor from this pin to ground to provide loop compensation.

Operation status output (analog output)
Pin is at 4.5V (nominal) during normal operation.
Pin switches to a lower voltage to indicate specific operation warnings or fault conditions. (See section
on STATUS output.)
Status pin voltage is low during shutdown mode.

Not Connected internally – recommend connection to pin 7, (PGND), to maximize PCB copper for

thermal dissipation

Not Connected internally – recommend connection pin 10 (GATE) to permit wide copper trace to gate

of MOSFET

Auxiliary positive supply to internal switch gate driver.
Connect to V

to application section for more details)
Decouple to ground with capacitor close to device (refer to Applications section)

Input supply to device (6V to 60V).
Decouple to ground with capacitor close to device (refer to Applications section)

Current monitor input. Connect current sense resistor between this pin and V
The nominal voltage across the resistor is 225mV

Flag open drain output.
Pin is high impedance during normal operation
Pin switches low to indicate a fault, or warning condition

Digital PWM output current control.
Pin driven either by open Drain or push-pull 3.3V or 5V logic levels.
Drive with frequency higher than 100Hz to gate output ‘on’ and ‘off’ during dimming control.
The device enters standby mode when PWM pin is driven with logic low level for more than 15ms

nominal (Refer to application section for more details)

Gain setting input.
Used to set the device in Buck mode or Boost, Buck-boost modes
Connect to ADJ in Buck mode operation
For Boost and Buck-boost modes, connect to resistive divider from ADJ to SGND. This defines the ratio

of switch current to LED current (see application section). The GI pin has an internal clamp that limits
the internal

, or auxiliary supply from 6V to 15V supply to reduce internal power dissipation (Refer

IN

node to less than 3V. This provides some failsafe should they get overdriven

www.diodes.com

< 2.5V) to adjust output current from 10% to 200% of set value.

ADJ

3 of 39

node to less than 3V. This provides some

IN

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Absolute Maximum Ratings (Note 5) (Voltages to GND, unless otherwise specified.)

Symbol Parameter Rating Unit

VIN

V

AUX

V

ISM

V

SENSE

V

GATE

I

GATE

V

FLAG

V

, V

PWM

ADJ

, VGI

V

TADJ

TJ

TST

Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only; functional
operation of the device at these or any other conditions exceeding those indicated in this specification is not implied. Device reliability may be affected by exposure to
absolute maximum rating conditions for extended periods of time.

Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and
transporting these devices.

Input Supply Voltage Relative to GND -0.3 to +65 V

Auxiliary Supply Voltage Relative to GND -0.3 to +65 V

Current Monitor Input Relative to GND -0.3 to +65 V

Current Monitor Sense Voltage (VIN-V

Gate Driver Output Voltage -0.3 to +20 V

ISM

)

-0.3 to +5 V

Gate Driver Continuous Output Current 18 mA

Flag Output Voltage -0.3 to 40 V

,

Other Input Pins -0.3 to +5.5 V

Maximum Junction Temperature 150 °C

Storage Temperature -55 to +150 °C

Package Thermal Data

Thermal Resistance Package Typical Unit

Junction-to-Ambient, 

(Note 6)

JA

Junction-to-Case, JC

Notes: 5. For correct operation SGND and PGND should always be connected together.

6. Measured on High Effective Thermal Conductivity Test Board" according JESD51.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

TSSOP-16EP 50 °C/W

TSSOP-16EP 23 °C/W

4 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Recommended Operating Conditions (@T

Symbol Parameter Performance/Comment Min Max Unit

VIN

V

AUX

V

ISM

V

SENSE

V

ADJ

I

REF

f

max

V

TADJ

f

PWM

t

PWMH/L

V

PWMH

V

PWML

TJ

GI Gain setting ratio for boost and buck-boost modes

Notes: 7. Device starts up above 6V and as such the minimum applied supply voltage has to be above 6.5V (plus any noise margin). The ZXLD1370 will,
however, continue to function when the input voltage is reduced from  8V down to 6.3V.
When operating with input voltages below 8V the output current and device parameters may deviate from their normal values; and is dependent on
power MOSFET switch, load and ambient temperature conditions. To ensure best operation in Boost and Buck-Boost modes with input voltages, V

between 6.3 and 8V a suitable boot-strap network on V
Performance in Buck mode will be reduced at input voltages (V

8. V
not be applied to V

9. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum operating frequency is not
tested in production.

Input supply voltage range

Auxiliary supply voltage range (Note 8)

Current sense monitor input range 6.3 60 V

Differential input voltage

External dc control voltage applied to ADJ
pin to adjust output current

Reference external load current REF sourcing current 1 mA

Recommended switching frequency range
(Note 9)

Temperature adjustment (T

) input voltage range

ADJ

Recommended PWM dimming frequency range

PWM pulse width in dimming mode PWM input high or low 0.002 10 ms

PWM pin high level input voltage 2 5.5 V

PWM pin low level input voltage 0 0.4 V

Operating Junction Temperature Range -40 125 °C

can be driven from a voltage higher than VIN to provide higher efficiency at low VIN voltages, but to avoid false operation; a voltage should

AUX

in the absence of a voltage at VIN.

AUX

= +25°C, unless otherwise specified.)

A

Normal operation 8

Reduced performance operation
(Note 7)

Normal operation 8

Reduced performance operation
(Note 7)

V

VIN-VISM

, with 0  V

ADJ

DC brightness control mode
from 10% to 200%

300 1000 kHz

0

To achieve 1000:1 resolution 100 500 Hz

To achieve 500:1 resolution 100 1000 Hz

Ratio = V

pin is recommended.

AUX

, V

) below 8V. – a boot-strap network cannot be implemented in buck mode.

IN

AUX

GI/VADJ

 2.5

6.3

6.3

60 V

60 V

0 450 mV

0.125 2.5 V

V

REF

V

0.20 0.50

,

IN

ZXLD1370

Document number: DS32165 Rev. 5 - 2

5 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Electrical Characteristics (Note 5) (V

Symbol Parameter Conditions Min Typ Max Units

Supply and Reference Parameters

V

UV-

V

UV+

I

Q-IN

I

Q-AUX

I

SB-IN

I

SB-AUX

V

REF

ΔV

REF

V

REF_LINE

V

REF-TC

DC-DC Converter Parameters

V

ADJ

I

ADJ

VGI

IGI

I

PWM

t

PWMoff

T

SDH

T

SDL

High-Side Current Monitor (Pin ISM)

I

ISM

V

SENSE

V

SENSE_acc

V

SENSE-OC

Notes: 10. The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This provides some failsafe should those pins get overdriven.

11. Initial sense voltage in Boost and Buck-Boost modes at maximum duty cycle.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

Under-Voltage detection threshold
Normal operation to switch disabled

Under-Voltage detection threshold
Switch disabled to normal operation

Quiescent current into VIN

Quiescent current into V

AUX

Standby current into VIN.

Standby current into V

Internal reference voltage No load 1.237 1.250 1.263 V

Change in reference voltage with output
current

Reference voltage line regulation

Reference temperature coefficient +/-50 ppm/°C

External dc control voltage applied to ADJ pin
to adjust output current (Note 8)

ADJ input current (Note 10)

AUX

.

GI Voltage threshold for boost and buck-boost
modes selection (Note 8)

GI input current (Note 10)

PWM input current

PWM pulse width
(to enter shutdown state)

Thermal shutdown upper threshold
(GATE output forced low)

Thermal shutdown lower threshold
(GATE output re-enabled)

Input Current

Current measurement sinse voltage

Accuracy of nominal V

Over-current sense threshold voltage 300 350 375 mV

threshold voltage

SENSE

IN

= V

=12V, TA = +25°C, unless otherwise specified.)

AUX

VIN or V

VIN or V

AUX

AUX

falling

rising

PWM pin floating.
Output not switching

PWM pin grounded
for more than 15ms

Sourcing 1mA -5

Sinking 100µA 5

VIN = V

, 6.5V<VIN = <60V

AUX

DC brightness control mode
10% to 200%

V

 2.5V

ADJ

= 5.0V†

V

ADJ

V

= 1.25V

ADJ

V

 2.5V

GI

= 5.0V†

V

GI

V

= 5.5V

PWM

PWM input low 10 15 25 ms

Temperature rising. 150 °C

Temperature falling. 125 °C

@ V

= 12V

ISM

Buck

Boost (Note 11) 225

V

ADJ

= 1.25V

Buck-Boost (Note 11)

V

= 1.25V

ADJ

6 of 39

www.diodes.com

5.2 5.6 6.3 V

5.5 6.0 6.5 V

1.5 3.0 mA

150 300 µA

90 150 µA

0.7 10.0 µA

mV

-60 -90 dB

0.125 1.25 2.50 V

100

5

nA
µA

0.8 V

100

5

nA
µA

36 100 µA

11 20 µA

218

mV

±0.25 ±2 %

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Electrical Characteristics (cont.) (V

Symbol Parameter Conditions Min Typ Max Units

Output Parameters

V

FLAGL

I

FLAGOFF

V

STATUS

R

STATUS

Driver output (PIN GATE)

V

GATEH

V

GATEL

V

GATECL

I

GATE

t

STALL

LED Thermal control circuit (T

V

TADJH

V

TADJL

I

TADJ

Notes: 12. In the event of more than one fault/warning condition occurring, the higher priority condition will take precedence. E.g. ‘Excessive coil current’ and
‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. The voltage levels on the STATUS output assume the
Internal regulator to be in regulation and V
minimum value of 6V.

13. Flag is asserted if V

14. GATE is switched to the supply voltage V
internally to prevent it exceeding 15V.

15. GATE is switched to PGND by an NMOS transistor

16. If t
grounded internally and the SHP pin is switched to its nominal operating voltage, before operation is allowed to resume. Restart cycles will be
repeated automatically until the operating conditions are such that normal operation can be sustained. If t
until normal operation is possible.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

FLAG pin low level output voltage Output sinking 1mA 0.5 V

FLAG pin open-drain leakage current

STATUS Flag no-load output voltage
(Note 12)

Output impedance of STATUS output Normal operation 10 k

High level output voltage

Low level output voltage Sinking 1mA, (Note 15) 0.5 V

High level GATE CLAMP voltage

Dynamic peak current available during rise
or fall of output voltage

Time to assert ‘STALL’ flag and
warning on STATUS output
(Note 16)

) parameters

ADJ

Upper threshold voltage

Lower threshold voltage

T

pin Input current V

ADJ

<2.5V or V

exceeds t

ON

SHP

, the device will force GATE low to turn off the external switch and then initiate a restart cycle. During this phase, ADJ is

STALL

SHP

= V

IN

<=V

ADJ

>3.5V

for low values of V

AUX

=12V, TA = +25°C, unless otherwise specified.)

AUX

V

FLAG

=40V

1 µA

Normal operation 4.2 4.5 4.8

Out of regulation (V
(Note 13)

VIN under-voltage (V

Switch stalled (tON or t

Over-temperature (TJ > +125°C)

Excess sense resistor current
(V

> 0.32V)

SENSE

No load Sourcing 1mA
(Note 14)

V

= V

AU X

= 1mA

= V

IN

I

GATE

Charging or discharging gate of external
switch with Q

G

out of range)

SHP

< 5.6V)

IN

> 100µs)

OFF

= 18V

ISM

= 10nC and 400kHz

3.3 3.6 3.9

3.3 3.6 3.9

3.3 3.6 3.9

1.5 1.8 2.1

0.6 0.9 1.2

10 11 V

12.8 15.0 V

±300 mA

GATE low or high 100 170 µs

Onset of output current reduction
(V

falling)

TADJ

Output current reduced to <10% of set
value (V

TADJ

. A reduction of the voltage on the STATUS pin will occur when the voltage on VIN is near the

REF

falling)

TADJ

= 1.25V

(i.e. between 6V and approximately 12V). For V

AUX

7 of 39

www.diodes.com

560 625 690 mV

380 440 500 mV

1 µA

>12V, GATE is clamped

AUX

exceeds t

OFF

, the switch will remain off

STALL

September 2012

© Diodes Incorporated

V

A

f

U

P

PLY

CUR

REN

T

REFERENC

OLTAG

CUR

REN

T

N

G FACTO

R

Typical Characteristics

3

Product Line o

Diodes Incorporated

ZXLD1370

1.252

2.5

2

t (mA)

1.5

1

S

0.5

0

6 121824 303642 485460

Figure 1 Supply Current vs. Supply Voltage

100%

80%

60%

SUPPLY VOLTAGE (V)

1.2515

1.251

E (V)

1.2505

1.25

E V

1.2495

1.249

1.2485

1.248

-40 -25 -10 5 20 35 50 65 80 95 110 125

1500

1250

1000

JUNCTION TEMPERATURE (°C)

Figure 2 V vs. Temperature

REF

DIMMI

40%

20%

LED

0%

0 250 500 750 1000 1250

ZXLD1370

Document number: DS32165 Rev. 5 - 2

T PIN VOLTAGE (mV)

ADJ

Figure 3 LED Current vs. T Voltage

ADJ

8 of 39

www.diodes.com

750

500

LED CURRENT (mA)

250

0

0 1020304050 60708090100

PWM DUTY CYCLE (%)

Figure 4 I vs. PWM Duty Cycle

LED

September 2012

© Diodes Incorporated

A

f

C

R

Q

C

CUR

RENT

UTY

Typical Characteristics (cont.)

1500

1250

1000

750

500

LED CURRENT (mA)

250

0

0

Figure 5 Buck LED Current, Switching Frequency vs. V

0.5
ADJ VOLTAGE (V)

1

1.5

Product Line o

Diodes Incorporated

ZXLD1370

900

700
650

750

SWITCHING FREQUENCY (kHz)

600

550

500

600

450

300

150

0

2

2.5

ADJ

450

400

I

LED

350

300

Switc hing
Frequency

250

LED CURRENT (mA)

200

150

100

50

0

0 0.5 1 1.5 2 2.5

ADJ VOLTAGE

T = 25°C

A

V = V = 24V

AUX IN

8LEDs

µ

L = 33 H
GI = 0.23
R = 300m

S

Figure 6 Buck-Boost LED Current, Switching Frequency vs. V

1400

1200

SWITCHING FREQUENCY (kHz)

1000

800

600

400

200

Ω

0

ADJ

700
650

600

550

500

450

(mA)

400

I

LED

350

300

Switching
Frequency

250

LED

200

150

100

50

0

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

ADJ VOLTAGE

T = 25°C

A

V = V = 12V

AUX IN

12 LEDs
L = 33 H

µ

R = 300m

Ω

S

Figure 7 Boost LED Current, Switching Frequency vs. V

700

600

500

400

300

200

100

0

ADJ

SWIT

HING F

E
UEN

Y(kHz)

100%

T = 25C

90%

80%

A

L = 33µH
R = 150m

S

Buck Mode
2 LEDS

70%

60%

50%

D

40%

30%

20%

10%

0%

6 121824303642485460

INPUT VOLTAGE (V)

Figure 8 Duty Cycle vs. Input Voltage

°

Ω

ZXLD1370

Document number: DS32165 Rev. 5 - 2

9 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

CUR

RENT

TCHING F

REQ

UENC

Y (k

H

F

F

C

C

Y

Typical Characteristics (cont.) Buck Mode – R

1.500

1 LED 3 LEDs

1.490

T = 25C

°

A

V = V

1.480

(A)

AUX IN

1.470

1.460

LED

1.450

1.440

1.430

6.5 11 15.5 20 24.5 29 33.5 38 42.5 47 51.5 56 60.5

Figure 9 Load Current vs. Input Voltage & Number of LED

5 LEDs

= 150m, L = 33µH

S

7 LEDs 9 LEDs

INPUT VOLTAGE (V)

Diodes Incorporated

11 L EDs 13 LEDs

Product Line o

ZXLD1370

15 LEDs

1000

1 LED 3 LEDs 5 L EDs 7 LEDs 9 LEDs 11 LED s 13 LEDs 15 LEDs

900

z)

800

700

T = 25°C

A

V = V

AUX IN

600

500

400

300

200

SWI

100

0

6.5 11 15.5 20 24.5 29 33.5 38 42.5 47 51.5 56 60.5

INPUT VOLTAGE (V)

Figure 10 Frequency vs. Input Voltage & Number of LED

100

95

90

85

(%)

80

IEN
I

75

T = 25°C

E

A

V = V

AUX IN

70

65

60

6.5 11 15.5 20 24.5 29 33.5 38 42.5 47 51.5 56 60.5
INPUT VOLTAGE (V)

Figure 11 Efficiency vs. Input & Number of LED

ZXLD1370

Document number: DS32165 Rev. 5 - 2

10 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

F

FIC

C

Y

Typical Characteristics (cont.) Buck Mode – R

0.740

0.735

0.730

0.725

LED CURRENT (A)

0.720

2 LEDs 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 L ED s 13 LEDs 15 LEDs

0.715

6.5 11 15.5 20 24.5 29 33.5 38 42.5 47 51.5 56 60.5

Figure 12 I vs. Input & Number of LED

1000

900

800

700

600

500

400

300

200

SWITCHING FREQUENCY (kHz)

100

0

100

2 LEDs 3 LEDs

T = 25°C

A

V = V

AUX IN

5 LEDs 7 LEDs 9 LEDs 11 L EDs 13 LEDs 15 LEDs

6.5 11 15.5 20 24.5 29 33.5 38 42.5 47 51.5 56 60.5

Figure 13 Frequency ZXLD1370 - Buck Mode - L47µH

= 300m, L = 47µH

S

INPUT VOLTAGE (V)

LED

INPUT VOLTAGE (V)

Product Line o

Diodes Incorporated

T = 25°C

A

V = V

AUX IN

ZXLD1370

95

90

85

(%)

80

T = 25°C

IEN

75

A

V = V

AUX IN

E

70

2 LEDs 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LED s 13 LEDs 15 LEDs

65

60

6.5 11 15.5 20 24.5 29 33.5 38 42.5 47 51.5 56 60.5
INPUT VOLTAGE (V)

Figure 14 Efficiency vs. Input Voltage & Number of LED

ZXLD1370

Document number: DS32165 Rev. 5 - 2

11 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Typical Characteristics (cont.) Boost Mode – R

0.400

0.350

0.300

0.250

0.200

0.150

LED CURRENT (A)

0.100

= 150m, GI

S

RATIO

Diodes Incorporated

= 0.23, L = 33µH

Product Line o

T = 25°C

A

V = V

AUX IN

ZXLD1370

0.050

3 LEDs 4 LEDs 6 LEDs 8 LEDs 10 LEDs 12 LEDs 14 LEDs 16 LEDs

0.000

6.5 10 13.5 17 20.5 24 27.5 31 34.5 38 41.5 45 48.5
INPUT VOLTAGE (V)

500

450

400

Figure 15 I vs. Input Voltage & Number of LED

3 LEDs 4 LEDs 6 LEDs 8 LEDs 10 LEDs 12 LEDs 14 LEDs 16 LEDs

T = 25°C

A

V = V

AUX IN

LED

350

300

250

200

150

SWITCHING FREQUENCY (kHz)

100

50

6.51013.5

17

Boosted voltage across

LEDs approaching VIN

20.5 24 27.5 31 34.5 38 41.5 45 48.5
INPUT VOLTAGE (V)

Figure 16 Frequency vs. Input Voltage & Number of LED

100

3 LEDs

4 LEDs

6 LEDs 8 LEDs 10 LEDs

12 LEDs 14 LEDs 16 LEDs

95

90

85

80

75

EFFICIENCY (%)

70

T = 25°C

A

V = V

AUX IN

65

60

6.5 10 13.5 17

20.5

24 27.5 31 34.5 38 41.5 45 48.5

INPUT VOLTAGE (V)

Figure 17 Efficiency vs. Input Voltage & Number of LED

ZXLD1370

Document number: DS32165 Rev. 5 - 2

12 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

C

URRENT

TCHING F

REQ

UENC

Y (k

H

F

F

C

C

Y

Typical Characteristics (cont.) Buck-Boost Mode – R

0.370

0.365

0.360

(A)

0.355

0.350

0.345

LED

0.340

0.335

0.330

6.5 8 9.5 11 12.5 14 15.5 17

800

700

z)

600

3 LEDs 4 LEDs 5 LEDs 6 LEDs 7 LEDs 8 LEDs

Figure 18 LED Current vs. Input Voltage & Number of LED

3 LEDs 4 LEDs 5 LEDs 6 LEDs 7 LEDs 8 LEDs

= 150m, GI

S

INPUT VOLTAGE (V)

RATIO

Product Line o

Diodes Incorporated

ZXLD1370

= 0.23, L = 47µH

500

400

300

200

SWI

100

0

6.5 8 9.5 11 12.5 14 15.5 17
INPUT VOLTAGE (V)

100

95

90

85

(%)

80

IEN
I

75

E

70

Figure 19 Switching Frequency vs. Input Voltage & Number of LED

3 LEDs 4 LEDs 5 LEDs 6 LEDs 7 LEDs 8 LEDs

65

60

6.5 8 9.5 11 12.5 14 15.5 17

Figure 20 Efficiency vs. Input Voltage & Number of LED

ZXLD1370

Document number: DS32165 Rev. 5 - 2

INPUT VOLTAGE (V)

13 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

c

c

e

t

V

a

t

f

t

o

s

T

a

c

T

a

T

c

T

a

s

c

Product Line o

Diodes Incorporated

ZXLD1370

Application Information

The ZXLD1370 is a high accuracy hysteretic inductive buck/boost/buck-boost controller designed to be used with an external NMOS switch for

current-driving single or multiple series-connected LEDs. The device can be configured to operate in buck, boost, or buck-boost modes by

suitable configuration of the external components as shown in the schematics shown in the device operation description.

Device Description
a) Buck mode – the most simple buck circuit is shown in Figure 21

Control of the LED current buck mode is achieved by sensing the coil

urrent in the sense resistor Rs, connected between the two inputs of a

urrent monitor within the control loop block. An output from the control

loop drives the input of a comparator which drives the gate of the

xternal NMOS switch transistor Q1 via the internal Gate Driver. When

he switch is on, the drain voltage of Q1 is near zero. Current flows from

IN, via Rs, LED, coil and switch to ground. This current ramps up until

n upper threshold value is reached (see Figure 22). At this point

GATE goes low, the switch is turned off and the drain voltage increases

o VIN plus the forward voltage, VF, of the schottky diode D1. Current

lows via RS, LED, coil and D1 back to VIN. When the coil current has

ramped down to a lower threshold value, GATE goes high, the switch is

urned on again and the cycle of events repeats, resulting in continuous

scillation. The feedback loop adjusts the NMOS switch duty cycle to

tabilize the LED current in response to changes in external conditions,

including input voltage and load voltage.

he average current in the sense resistor, LED and coil is equal to the

verage of the maximum and minimum threshold currents. The ripple

urrent (hysteresis) is equal to the difference between the thresholds.

he control loop maintains the average LED current at the set level by

djusting the switch duty cycle continuously to force the average sense

resistor current to the value demanded by the voltage on the ADJ pin.

his minimizes variation in output current with changes in operating

onditions.

he control loop also regulates the switching frequency by varying the

level of hysteresis. The hysteresis has a defined minimum (typ 5%) and

maximum (typ 30%). The frequency may deviate from nominal in

ome conditions. This depends upon the desired LED current, the coil

inductance and the voltages at the input and the load. Loop

ompensation is achieved by a single external capacitor C2, connected

between SHP and SGND.

Figure 21 Buck Configuration

The control loop sets the duty cycle so that the sense voltage is

⎞

⎛

V

ADJ

⎟

⎜

=

V

SENSE

Therefore,

=

I

LED

If the ADJ pin connected to the REF pin, this simplifies to

=

I

LED

218.0

⎜
⎝

⎞

⎛
⎜

⎜
⎝

⎛
⎜

⎜
⎝

⎛

218.0

V

⎟

⎜
⎜

⎟

V

R

S

⎝

⎠

⎞

⎛

218.0

V

⎟

⎜
⎜

⎟

V

R

S

⎝

⎠

ZXLD1370

Document number: DS32165 Rev. 5 - 2

⎟

V

REF

⎠

⎞

ADJ

⎟

(Buck mode) Equation 1

⎟

REF

⎠

⎞

ADJ

⎟

(Buck mode)

⎟

REF

⎠

14 of 39

www.diodes.com

Figure 22 Operating Waveforms (Buck Mode)

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

b) Boost and Buck-Boost modes – the most simple boost/buck-boost circuit is shown in Figure 23

Control in Boost and Buck-boost mode is achieved by sensing the coil

current in the series resistor Rs, connected between the two inputs of a

current monitor within the control loop block. An output from the control loop

drives the input of a comparator which drives the gate of the external NMOS

switch transistor Q1 via the internal Gate Driver. When the switch is on, the

drain voltage of Q1 is near zero. Current flows from VIN, via Rs, coil and

switch to ground. This current ramps up until an upper threshold value is

reached (see Figure 24). At this point GATE goes low, the switch is turned

off and the drain voltage increases to either:

1) the load voltage VLEDS plus the forward voltage of D1 in Boost

or

Current flows via Rs, coil, D1 and LED back to VIN (Buck-boost mode), or

GND (Boost mode). When the coil current has ramped down to a lower

threshold value, GATE goes high, the switch is turned on again and the

cycle of events repeats, resulting in continuous oscillation. The feeback

loop adjusts the NMOS switch duty cycle to stabilize the LED current in

response to changes in external conditions, including input voltage and load

voltage. Loop compensation is achieved by a single external capacitor C2,

connected between SHP and SGND. Note that in reality, a load capacitor

C

OUT

The average current in the sense resistor and coil, I

average of the maximum and minimum threshold currents and the ripple

current (hysteresis) is equal to the difference between the thresholds.

The average current in the LED, I

control loop adjusts the switch duty cycle, D, to achieve a set point at the

sense resistor. This controls I

flows through D1 and the LED load. During t

through Q1, not the LEDs. Therefore the set point is modified by D using a

gating function to control I

for the effect of the gating function, a control factor, GI_ADJ is used.

GI_ADJ is set by a pair of external resistors, R

This allows the sense voltage to be adjusted to an optimum level for power

efficiency without significant error in the LED controlled current.

The control loop sets the duty cycle so that the sense resistor current is

I

RS

schottky diode. The schottky diode passes the LED current.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

configuration,

2) the load voltage VLEDS plus the forward voltage of D1 plus VIN in

Buck-boost configuration.

is used, so that the LED current waveform shown is smoothed.

, is equal to the

RS

, is always less than IRS. The feedback

LED

. During the interval t

RS

ON

indirectly. In order to compensate internally

LED

GI1

1RGI

⎛

ADJ_GI

⎜
⎝

Equation 2 (Boost and Buck-boost modes)

⎞

⎛

225.0

⎜

=

R

S

⎜

R

S

⎝

Equation 3 (Boost and Buck-boost modes)

equals the coil current. The coil is connected only to the switch and the

ADJ_GI

⎛

⎟

⎜

⎟

−

D1

⎝

⎠

⎞
⎟

+=2RGI1RGI

⎠

⎛

⎞

V

ADJ

⎜

⎟

⎜

V

⎠

REF

⎝

, the coil current

OFF

, the coil current flows

and R

. (Figure 23.)

GI2

⎞
⎟

⎟
⎠

www.diodes.com

15 of 39

Figure 23 Boost and Buck-Boost Configuration

Figure 24 Operating Waveforms

(Boost and Buck-boost modes)

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Therefore the average LED current is the coil current multiplied by the schottky diode duty cycle, 1-D.

⎞

RSLED

This shows that the LED current depends on the ADJ pin voltage, the reference voltage and 3 resistor values (RS, RGI1 and RGI2). It is

independent of the input and output voltages.

If the ADJ pin is connected to the REF pin, this simplifies to

⎞

⎛

225.0

⎟

⎜

=

I

LED

Now I

LED

Considering power dissipation and accuracy, it is useful to know how the mean sense voltage varies with input voltage and other parameters.

This shows that the sense voltage varies with duty cycle in Boost and Buck-Boost configurations.

⎟

⎜

R

S

⎠

⎝

is dependent only on the 3 resistor values.

==

225.0

IV

RSRS

⎟

⎜

R

S

⎠

⎝

ADJ_GI

(Boost and Buck-Boost)

ADJ_GI

⎛
⎜

−

D1

⎝

⎛

225.0

⎟

⎜

D1

=−=

()

II

Application Circuit Design

External component selection is driven by the characteristics of the load and the input supply, since this will determine the kind of topology being

used for the system. Component selection begins with the current setting procedure, the inductor/frequency setting and the MOSFET selection.

Finally after selecting the freewheeling diode and the output capacitor (if needed), the application section will cover the PWM dimming and

thermal feedback. The full procedure is greatly accelerated by the web Calculator spreadsheet, which includes fully automated component

selection, and is available on the Diodes web site. However the full calculation is also given here.

Some components depend upon the switching frequency and the duty cycle. The switching frequency is regulated by the ZXLD1370 to a large

extent, depending upon conditions. This is discussed in a later paragraph dealing with coil selection.

Duty Cycle Calculation and Topology Selection

The duty cycle is a function of the input and output voltages. Approximately, the MOSFET switching duty cycle is

V

OUT

≈ for Buck

D

BUCK

D

BOOST

D

BB

Because D must always be a positive number less than 1, these equations show that

V

V

V

This allows us to select the topology for the required voltage range.

V

IN

−

VV

≈

V

OUT

≈

OUT

OUT

OUT

INOUT

V

+

VV

< VIN for Buck (voltage step-down)

> VIN for Boost (voltage step-up)

> or = or < VIN for Buck-boost (voltage step-down or step-up)

for Boost Equation 6

OUT

for Buck-Boost

INOUT

⎛

⎞

V

ADJ

⎜

ADJ_GI

⎛

⎞

V

ADJ

⎜

⎟

⎜

V

⎠

REF

⎝

⎟

⎜
⎝

(Boost and Buck-Boost) Equation 4

⎟

V

REF

⎠

⎞
⎟

(Boost and Buck-Boost) Equation 5

⎟
⎠

ZXLD1370

Document number: DS32165 Rev. 5 - 2

16 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

More exact equations are used in the web Calculator. These are:

()

+++

RRIVV

=

D

BUCK

D

D

where V

V

R

The additional terms are relatively small, so the exact equations will only make a significant difference at lower operating voltages at the input

and output, i.e. low input voltage or a small number of LEDs connected in series. The estimates of V

The mean coil current, I

I

I

I

I

LED

power efficiency. If the expected efficiency is roughly 90%, the output power P

estimated as follows.

P

or I

where N is the number of LEDs connected in series, and V

So

Equation 9 can now be used to find I

calculation of Duty Cycle and the selection of Buck, Boost or Buck-boost topology.

An initial estimate of duty cycle is required before we can choose a coil. In Equation 7, the following approximations are recommended:

Then Equation 7 becomes

COIL

is the target LED current and is already known. IIN will be calculated with some accuracy later, but can be estimated now from the electrical

LED

I

IN

V

I

IN(RS+RCOIL

I

OUT(RS+RCOIL

V

(I

IN+IOUT

D

D

D

=

BOOST

=

BB

= schottky diode forward voltage, estimated for the expected coil current, I

F

= MOSFET drain source voltage in the ON condition (dependent on R

DSON

= DC winding resistance of L1

COIL

depends upon the topology and upon the mean terminal currents as follows:

COIL

= IIN for Boost Equation 8

 0.9 P

OUT

N V

 0.9 IIN VIN

LED

N

V

I

≈ Equation 9

= 0.5V

F

DSON

BUCK

BOOST

BB

LEDLED

9.0

V

IN

) = 0.5V

) = 0.5V

= 0.1V

)(RS+R

COIL

+

V

OUT

≈

+

V

IN

≈

V

OUT

+

V

OUT

≈

VV

INOUT

−+

VVV

()

()( )

for Buck

LED

+ I

for Buck-boost

IN

LED

IN

COIL

) = 1.1V

1

for Buck

4.0

1

+−

VV

INOUT

for Boost Equation 7a

4.0

+

6.1

for Buck-boost

4.0

++

COILSOUTFOUT

++++

RRIIVV

COILSOUTINFOUT

for Buck

+++−

VRRIVV

FCOILSININOUT

for Boost Equation 7

for Buck-boost

COIL

and drain current = I

DSON

is 90% of the input power, PIN, and the coil current is

OUT

is the forward voltage drop of a single LED at I

LED

and V

F

)

COIL

depend on the coil current.

DSON

.

LED

DSONFIN

−+

VVV

DSONFOUT

−++

VVVV

DSONFINOUT

in Equation 8, which can then be used to estimate the small terms in Equation 7. This completes the

ZXLD1370

Document number: DS32165 Rev. 5 - 2

17 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Setting the LED current

The LED current requirement determines the choice of the sense resistor Rs. This also depends on the voltage on the ADJ pin and the voltage

on the GI pin, according to the topology required.

The ADJ pin may be connected directly to the internal 1.25V reference (V

driven with an external dc voltage between 125mV and 2.5V to adjust the LED current proportionally between 10% and 200% of the nominal

value.

For a divider ratio GI_ADJ greater than 0.65V, the ZXLD1370 operates in Buck mode when V

the device operates in Boost or buck-Boost mode, according to the load connection. This 0.65V threshold varies in proportion to V

Buck mode threshold voltage is 0.65 V

ADJ and GI are high impedance inputs within their normal operating voltage ranges. An internal 2.6V clamp protects the device against

excessive input voltage and limits the maximum output current to approximately 4% above the maximum current set by V

input voltage is exceeded.

/1.25V.

ADJ

Buck Topology

In Buck mode, GI is connected to ADJ as in Figure 25. The LED current depends only

upon R

, V

and V

S

If ADJ is directly connected to VREF, this becomes:

ADJ

R

SBUCK

R

SBUCK

. From Equation 1 above,

REF

⎛
⎜

=

⎜
⎝

⎛
⎜

=

⎜
⎝

I

LED

I

LED

⎞

⎛

218.0

⎟
⎟

⎠

⎞

218.0

⎟
⎟

⎠

⎞

V

ADJ

⎜

⎟

⎜

⎟

V

REF

⎝

⎠

Equation 10

) to define the nominal 100% LED current. The ADJ pin can also be

REF

= 1.25V. If GI_ADJ is less than 0.65V (typical),

ADJ

, i.e., the

ADJ

if the maximum

REF

Figure 25 Setting LED Current in

Buck Configuration

Boost and Buck-Boost Topology

For Boost and Buck-boost topologies, the LED current depends upon the resistors, RS,

, and R

R

GI1

freedom. That is to say, there is not a unique solution. From Equation 4,

If ADJ is connected to REF, this becomes

GI_ADJ is given by Equation 2, repeated here for convenience:

Note that from considerations of ZXLD1370 input bias current, the recommended limits for R

22k < R

ZXLD1370

Document number: DS32165 Rev. 5 - 2

as in Equations 4 and 2 above. There is more than one degree of

GI2

⎛

R

SBOOSTBB

R

SBOOSTBB

ADJ_GI

⎞

225.0

⎜

=

=

⎛
⎜

⎝

< 100k Equation 12

GI1

⎟

⎜

⎟

I

LED

⎝

⎠

⎛

⎞

225.0

⎜

⎟

⎜

⎟

I

LED

⎝

⎠

1RGI

+=2RGI1RGI

⎞
⎟

⎠

ADJ_GI

ADJ_GI

⎛

V

ADJ

⎜
⎜

V

REF

⎝

⎞
⎟

Equation 11

⎟
⎠

18 of 39

www.diodes.com

Figure 26 Setting LED Current in Boost

and Buck-Boost Configuration

are:

GI1

September 2012

© Diodes Incorporated

A

f

(

)

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

The additional degree of freedom allows us to select GI_ADJ within limits but this may affect overall performance a little. As mentioned above,

the working voltage range at the GI pin is restricted. The permitted range of GI_ADJ in Boost or Buck-boost configuration is

0.2 < GI_ADJ < 0.5 Equation 13

The mean voltage across the sense resistor is

V

Note that if GI_ADJ is made larger, these equations show that R

dissipation in R

this becomes

This shows that V

GI_ADJ is the minimum value of 0.2, then V

offsets in the system, such as mV drop in the copper printed wiring circuit, or offset uncertainty in the ZXLD1370. If now, GI_ADJ is increased to

0.4 or 0.5, V

operation will be obtained if V

There is also a maximum limit on V

STATUS output may indicate an over-current condition. This will happen for larger D

Therefore, together with the requirement of Equation 13, the recommended range for GI_ADJ is

0.355 ( 1-D

An optimum compromise for GI_ADJ has been suggested, i.e.

GI_ADJ

This value has been used for the “Automatic” setting of the web Calculator. If 1-D

greater than 0.5 then GI_ADJ is set to 0.5.

Once GI_ADJ has been selected, a value of RGI1 can be selected from Equation 12.

Then RGI2 is calculated as follows, rearranging Equation 2:

For example to drive 12 LEDS at a current of 350mA from a 12V supply requires Boost configuration. Each LED has a forward voltage of 3.2V

at 350mA, so Vout = 3.2*12 = 38.4V. From Equation 6, the duty cycle is approximately

From Equation 16, we set GI_ADJ to 1 – D = 0.3125.

IF R

GI1

Let us choose the preferred value R

= I

RS

is increased. So, in some cases, it is better to minimize GI_ADJ. However, consider Equation 5. If ADJ is connected to REF,

S

V

RS

is increased to a value greater than 100mV. This will give small enough I

RS

=

V

OUT

V

OUT

= 33k, then from Equation 17,

= k6.72

R

2GI

ADJ_GI =

ZXLD1370

Document number: DS32165 Rev. 5 - 2

Equation 14

COIL RS

is increased and V

S

ADJ_GI

⎛

225.0

⎜
⎝

becomes smaller than 225mV if GI_ADJ < 1 - D. If also D is small, VRS can become too small. For example if D = 0.2, and

RS

) < GI_ADJ < 1.33 ( 1-D

MIN

= 1 - D

AUTO

⎛

−

⎜

RR

1GI2GI

⎜
⎝

−

⎛

V

IN

=

⎜
⎝

−

⎛

x33

⎜

3125.0

⎝

⎛

=

⎜
⎝

⎞
⎟

−=D1

⎠

becomes 0.225* 0.2 / 0.8 = 56.25 mV. This will increase the LED current error due to small

RS

is more than about 80mV. This means GI_ADJ should be greater than (1-D

RS

which gives a maximum limit for GI_ADJ. If VRS exceeds approximately 300mV, or 133% of 225mV, the

RS

) Equation 15

MAX

Equation 16

MAX

⎞

ADJ_GI1

⎟

Equation 17

⎟

ADJ_GI

⎠

124.38

−

⎞

6875.0

=

⎟

4.38

⎠

3125.01

⎞
⎟

Ω=

⎠

= 75k. Now GI_ADJ is adjusted to the new value, using Equation 2.

GI2

1RGI

⎞

=

⎟

2RGI1RGI

+

⎠

k33

+

305.0

k75k33

19 of 39

www.diodes.com

is increased. Therefore, for the same coil current, the

RS

error for most practical purposes. Satisfactory

LED

) * 80/225 = (1- D

MIN

.

MAX

is less than 0.2, then GI_ADJ is set to 0.2. If 1- D

MAX

MIN

September 2012

© Diodes Incorporated

) * 0.355.

MAX

is

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Now we calculate R

R

SBOOSTBB

A preferred value of R

Table 1 shows typical resistor values used to determine the GI_ADJ ratio with E24 series resistors

Table 1

GI ratio RGI1 RG2

0.2

0.25

0.3

0.35

0.4

0.45

0.5

This completes the LED current setting.

Inductor Selection and Frequency Control

The selection of the inductor coil, L1, requires knowledge of the switching frequency and current ripple, and also depends on the duty cycle to

some extent. In the hysteretic converter, the frequency depends upon the input and output voltages and the switching thresholds of the current

monitor. The peak-to-peak coil current is adjusted by the ZXLD1370 to control the frequency to a fixed value. This is done by controlling the

switching thresholds within particular limits. This effectively much reduces the overall frequency range for a given input voltage range. Where

the input voltage range is not excessive, the frequency is regulated to approximately 330kHz in Buck configuration, and 300kHz in Boost and

Buck-boost configurations. This is helpful in terms of EMC and other system requirements.

For larger input voltage variation, or when the choice of coil inductance is not optimum, the switching frequency may depart from the regulated

value, but the regulation of LED current remains successful. If desired, the frequency can to some extent be increased by using a smaller

inductor, or decreased using a larger inductor. The web Calculator will evaluate the frequency across the input voltage range and the effect of

this upon power efficiency and junction temperatures.

Determination of the input voltage range for which the frequency is regulated may be required. This calculation is very involved, and is not given

here. However the performance in this respect can be evaluated within the web Calculator for the chosen inductance.

The inductance is given as follows in terms of peak-to-peak ripple current in the coil, I

L1 =

Therefore In order to calculate L1, we need to find I

I

is estimated from Equation 9.

IN

from Equation 11. Assume ADJ is connected to REF.

S

⎞

= 196.0305.0x

⎟

⎜

I

LED

⎠

⎝

SBoostBB

30kΩ 120kΩ
33kΩ 100kΩ
39kΩ 91kΩ
30kΩ 56kΩ

100kΩ 150kΩ

51kΩ 62kΩ
30kΩ 30kΩ

⎞

⎛

225.0

⎟

⎜

⎛

V

ADJ

⎜

ADJx_xGI

⎜

V

REF

⎝

= 0.2 will give the desired LED current with an error of 2% due to the preferred value selection.

225.0

⎟
⎟

35.0

⎠

(){}

t

ON

(){}

()( ){}

++−

RRRIV

SCOILDSONININ

I

Δ

L

+++−

, tON, and IL. The effects of the resistances are small and will be estimated.

IN

Ω==

and the MOSFET on time, tON.

L

t

ON

++−−

RRRIVV

for Boost Equation 18

RRRIIV

SCOILDSONOUTININ

for Buck

SCOILDSONOUTLEDIN

I

Δ

L

t

ON

for Buck-boost

I

Δ

L

ZXLD1370

Document number: DS32165 Rev. 5 - 2

20 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

t

is related to switching frequency, f, and duty cycle, D, as follows:

ON

As the regulated frequency is known, and we have already found D from Equation 7 or the approximation Equation 7b, this allows calculation of

.

t

ON

The ZXLD1370 sets the ripple current, I

current, I

We therefore need to use a value of 20% of I

control is also modulated by other circuit parameters as follows.

If ADJ is connected to REF, this simplifies to

COIL

where I

The chosen coil should have a saturation current higher than the peak sensed current. This saturation current is the DC current for which the

inductance has decreased by 10% compared to the low current value.

Assuming ±10% ripple current, we can find this peak current from Equation 8, adjusted for ripple current:

1.1 I

I

1.1 I

where I

INMAX

The mean current rating is also a factor, but normally the saturation current is the limiting factor.

The following websites may be useful in finding suitable components

ZXLD1370

Document number: DS32165 Rev. 5 - 2

D

Equation 19

=

t

ON

f

is monitored by the ZXLD1370 which sets this to be between nominally 10% and 30% of the mean coil

L

, which is found from Equation 8. The device adjusts the ripple current within this range in order to regulate the switching frequency.

to find an inductance which is optimized for the input voltage range. The range of ripple current

COIL

⎧

Δ

Δ

Δ

Δ

Δ

Δ

LMID

COILPEAK

www.coilcraft.com
www.niccomp.com
www.wuerth-elektronik.de

⎪

I

⎨

LMAX

⎪

⎩

⎧

⎪

I

⎨

LMIN

⎪

⎩

⎧

⎪

I

⎨

LMID

⎪

⎩

=

I

I

I

is the value we must use in Equation 18. We have now established the inductance value.

is the value of IIN at minimum VIN.

15.0

05.0

=

1.0

=

= 1.1 I

⎛
⎜

+=

12.003.0

⎜
⎝

⎛
⎜

+=

04.001.0

⎜
⎝

⎛
⎜

+=

08.002.0

⎜
⎝

−

D1

ADJ_GI

D1

−

ADJ_GI

D1

−

I

COILLMID

ADJ_GI

LED

INMAX

INMAX

⎫

⎞

D1

−

⎪

V

ADJ

⎟

⎬

⎟

ADJ_GI

⎪

V

REF

⎠

⎭

⎫

⎞

V

ADJ

⎟
⎟

V

REF

⎠

V

ADJ

V

REF

I

COILLMAX

I

COILLMIN

for Buck

for Boost Equation 21

+ I

D1

−

⎪
⎬

ADJ_GI

⎪

⎭

⎫

⎞

D1

−

⎪

⎟

⎬

⎟

ADJ_GI

⎪

⎠

⎭

Equation 20a

for Buck-boost

LED

I

COIL

Equation 20

I

COIL

I

COIL

21 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

MOSFET Selection

The ZXLD1370 requires an external NMOS FET as the main power switch with a voltage rating at least 15% higher than the maximum circuit

voltage to ensure safe operation during the overshoot and ringing of the switch node. The current rating is recommended to be at least 10%

higher than the average transistor current. The power rating is then verified by calculating the resistive and switching power losses.

P

Resistive Power Losses

The resistive power losses are calculated using the RMS transistor current and the MOSFET on-resistance.

Calculate the current for the different topologies as follows:

Buck Mode

Boost / Buck-Boost Mode

The approximate RMS current in the MOSFET will be:

I

Buck Mode

Boost / Buck-Boost Mode

The resistive power dissipation of the MOSFET is:

I

Switching Power Losses

Calculating the switching MOSFET's switching loss depends on many factors that influence both turn-on and turn-off. Using a first order rough

approximation, the switching power dissipation of the MOSFET is:

where

C

RSS

f

SW

I

GATE

P =

SWITCHING

is the MOSFET's reverse-transfer capacitance (a data sheet parameter),

is the switching frequency,

is the MOSFET gate-driver's sink/source current at the MOSFET's turn-on threshold.

+=

PP

SWITCHINGRESISTIVE

−

D

MAX

=

MAXMOSFET

−

−

−

D1

MAX

DII

LEDRMSMOSFET=−

D

=

−

D1

=

RSS

RMSMOSFETRESISTIVE

IxDI =

LEDMAXMAXMOSFET

×

Ix

LEDRMSMOSFET

i

LED

2

IN

I

GATE

2

RxIP

ONDS

−−

IxfxVxC

LOADsw

ZXLD1370

Document number: DS32165 Rev. 5 - 2

22 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Matching the MOSFET with the controller is primarily based on the rise and fall time of the gate voltage. The best rise/fall time in the application

is based on many requirements, such as EMI (conducted and radiated), switching losses, lead/circuit inductance, switching frequency, etc. How

fast a MOSFET can be turned on and off is related to how fast the gate capacitance of the MOSFET can be charged and discharged. The

relationship between C (and the relative total gate charge Qg), turn-on/turn-off time and the MOSFET driver current rating can be written as:

Qg

CdV

dt =

where

dt = turn-on/turn-off time

dV = gate voltage

C = gate capacitance = Qg/V

Here the constant current source” I ” usually is approximated with the peak drive current at a given driver input voltage.

(Example 1)

Using the DMN6068 MOSFET (V

ZXLD1370 I

I = drive current – constant current source (for the given voltage value)

Æ Q

dt

Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this

condition is:

t

PERIOD

This frequency is well above the max frequency the device can handle, therefore the DNM6068 can be used with the ZXLD1370 in the whole

spectrum of frequencies recommended for the device (from 300kHz to 1MHz).

(Example 2)

Using the ZXMN6A09K (V

ZXLD1370 I

Æ Q

dt

Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this

condition is:

t

PERIOD

This frequency is within the recommended frequency range the device can handle, therefore the ZXMN6A09K is recommended to be used with

the ZXLD1370 for frequencies from 300kHz to 500kHz).

The recommended total gate charge for the MOSFET used in conjunction with the ZXLD1370 is less than 30nC.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

⋅

=

I

= 10.3nC at VGS = 10V

G

= I

PEAK

GATE

Q

g

I

PEAK

= 20*dt Æ f = 1/ t

= 29nC at VGS = 10V

G

= 300mA

PEAK

Q

g

I

PEAK

= 20*dt Æ f = 1/ t

I

= 300mA

nC3.10

mA300

DS(MAX)

nC29

mA300

DS(MAX)

===

= 60V, I

===

= 60V, I

ns35

D(MAX)

ns97

D(MAX)

= 1.43MHz

PERIOD

= 12.2A):

= 515kHz

PERIOD

= 8.5A):

23 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

Application Information (cont.)

Junction Temperature Estimation

Finally, the ZXLD1370 junction temperature can be estimated using the following equations:

Total supply current of ZXLD1370:

 IQ + f • QG

I

Power consumed by ZXLD1370

Or in case of separate voltage supply, with V

Where the total quiescent current IQ

power MOSFET. Moreover the part of thermal resistance between case and ambient depends on the PCB characteristics.

QTOT

Where I

P

P

T

= total quiescent current I

Q

= VIN • (IQ + f • Qg)

IC

= VIN • I

IC

= TA + PIC • θ

J

Q-IN

+ V

aux

• (I

JA

+ I

Q-IN

Q-AUX

< 15V

AUX

+ f • Qg)

Q-AUX

= TA + PIC • (θ

consists of the static supply current (IQ) and the current required to charge and discharge the gate of the

TOT

JC

+ θ

CA)

ZXLD1370

2.5

2

1.5

1

Power dissipation (mW)

0.5

0

-40 -25 -10 5 20 35 50 65 80 95 110 125

Ambient temperature (°C)

Figure 27 Power Derating Curve for ZXLD1370 Mounted on Test Board According to JESD51

ZXLD1370

Document number: DS32165 Rev. 5 - 2

24 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Diodes Selection

For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low reverse leakage at the

maximum operating voltage and temperature. The Schottky diode also provides better efficiency than silicon PN diodes, due to a combination of

lower forward voltage and reduced recovery time.

It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum

output load current. In particular, it is recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure

safe operation during the ringing of the switch node and a current rating at least 10% higher than the average diode current. The power rating is

verified by calculating the power loss through the diode.

The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the Drain of the

external MOSFET. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the Drain of the external

MOSFET, including supply ripple, does not exceed the specified maximum value.

*A suitable Schottky diode would be PDS3100 (Diodes Inc).

Output Capacitor

An output capacitor may be required to limit interference or for specific EMC purposes. For boost and buck-boost regulators, the output

capacitor provides energy to the load when the freewheeling diode is reverse biased during the first switching subinterval. An output capacitor in

a buck topology will simply reduce the LED current ripple below the inductor current ripple. In other words, this capacitor changes the current

waveform through the LED(s) from a triangular ramp to a more sinusoidal version without altering the mean current value.

In all cases, the output capacitor is chosen to provide a desired current ripple of the LED current (usually recommended to be less than 40% of

the average LED current).

Buck:

I

Δ

PPL

C

OUTPUT

=

Boost and Buck-Boost

The output capacitor should be chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS

current rating. The minimum RMS current for the output capacitor is calculated as follows:

C

OUTPUT

where:

• ΔI

• ΔI

• f

sw

• r

LED

datasheet of the LED manufacturer).

=

is the ripple of the inductor current, usually ± 20% of the average sensed current

L-PP

is the ripple of the LED current, it should be <40% of the LEDs average current

LED-PP

is the switching frequency (From graphs and calculator)

is the dynamic resistance of the LEDs string (n times the dynamic resistance of the single LED from the

Buck

I

COUTPUT

−

RMS

=

Boost and Buck-Boost

Ceramic capacitors with X7R dielectric are the best choice due to their high ripple current rating, long lifetime, and performance over the voltage

and temperature ranges.

=

−

ZXLD1370

Document number: DS32165 Rev. 5 - 2

−

Ixrxfx8

Δ

IxD

PPLED

−

Ixrxf

Δ

−

I

PPLED

−

PPLEDLEDSW

−

PPLEDLEDSW

12

D

MAX

II

LEDRMSCOUTPUT

−

D1

MAX

25 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Input Capacitor

The input capacitor can be calculated knowing the input voltage ripple ΔV

Buck

Ix)D1(xD

−

C

C

C

I

CIN−−

=

IN

=

IN

=

IN

=

RMS

=

−

Boost

Buck-Boost

The minimum RMS current for the output capacitor is calculated as follows:

Buck

Boost

Buck-Boost

ZXLD1370

Document number: DS32165 Rev. 5 - 2

LED

Vxf

Δ

I

Δ

−

IxD

LED

Vxf

Δ

LEDRMSCIN−=−

I

PPL

Use D = 0.5 as worst case

PPINSW

−

PPL

Vxfx8

Δ

−

PPINSW

−

Use D = D

PPINSW

use D = 0.5 as worst case

)D1(DxxII

as worst case

MAX

12

D

xII

LEDRMSCIN

Use D = D

)D1(

−

as worst case

MAX

26 of 39

www.diodes.com

IN-PP

as follows:

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

PWM Output Current Control & Dimming

The ZXLD1370 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with up to 1000:1

resolution; however higher dimming frequencies can be used – at the expense of dimming dynamic range and accuracy.

Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is better than 1% for PWM

from 5% to 100%. This is shown in the graph below:

Buck mode - L=33uH - Rs = 150mΩ - PWM @ 1kHz

1500.00

1250.00

1000.00

LED current [ mA]

750.00

500.00

250.00

0.00

0 102030405060708090100

PWM

PWM @ 1kHz Error

Figure 28 LED Current Linearity and Accuracy with PWM Dimming at 1kHz

10%

9%

8%

7%

6%

5%

4%

3%

2%

1%

0%

Error

For a PWM frequency of 100Hz, the error on the current linearity is lower than 2.5%; it becomes negligible for PWM greater than 5%. This is

shown in the graph below:

Buck mode - L=33uH - Rs = 150mΩ - PWM @ 100Hz

1500.0 0

1250.0 0

1000.0 0

LED current [ mA]

750.00

500.00

250.00

0.00

0 102030405060708090100

PWM

PWM @ 100Hz Error

Figure 29 LED Current Linearity and Accuracy with PWM Dimming at 100Hz

10%

9%

8%

7%

6%

5%

4%

3%

2%

1%

0%

Error

The PWM pin is designed to be driven by both 3.3V and 5V logic levels. It can be driven also by an open drain/collector transistor. In this case

the designer can either use the internal pull-up network or an external pull-up network in order to speed-up PWM transitions, as shown in the

Boost/ Buck-Boost section.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

27 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Application Information (cont.)

Gate

0V

Product Line o

Diodes Incorporated

2µs

ZXLD1370

< 10 ms

Figure 30. PWM Dimming from Open Collector Switch

Figure 31 PWM Dimming from MCU

LED current can be adjusted digitally, by applying a low frequency PWM logic signal to the PWM pin to turn the controller on and off. This

will produce an average output current proportional to the duty cycle of the control signal. During PWM operation, the device remains

powered up and only the output switch is gated by the control signal.

The PWM signal can achieve very high LED current resolution. In fact, dimming down from 100% to 0.1% at 500Hz, a minimum pulse width

of 2µs can be achieved resulting in very high resolution and accuracy. While the maximum recommended pulse is for the PWM signal is

10ms (equivalent to 100Hz) See Figure 32.

The ultimate PWM dimming ratio will be determined by the

switching frequency as the minimum PWM pulse width is

determined by resolving at least 1 switching cycle. The figure to the

right the switching waveforms for a low duty cycle PWM dimming.

As can be seen, when the LED current restarts (blue waveform) it

has to start all the way from zero to the peak level set by

V

SENSE/RS*

nominal switching frequency would imply.

1.15. So the first pulse is always longer than the

PWM

< 10 ms

0V

2

µs

Figure 32 PWM Dimming Minimum and Maximum Pulse

The PWM pin can be used to put the device into standby. Taking

the PWM pin low (<0.4V) for more than 25ms (typically 15ms) the

device will enter its standby state and most of the internal circuitry

is switched off and residual quiescent current will be typically 90µA.

In particular, the Status pin will go down to GND while the FLAG

and REF pins will stay at their nominal values.

When the device restarts from standby mode, a “start-up” time must be allowed for before the device resume full LED current regulation.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

Figure 33 Standby State from PWM signal

28 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Thermal Control of LED Current

For thermal control of the LEDs, the ZXLD1370 monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls

below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on the TADJ pin to

625mV at the required temperature threshold. This will give 100% LED current below the threshold temperature and a falling current above it as

shown in the graph. The temperature threshold can be altered by adjusting the value of Rth and/or the thermistor to suit the requirements of the

chosen LED.

The Thermal Control feature can be disabled by connecting TADJ directly to REF.

Here is a simple procedure to design the thermal feedback circuit:

1) Select the temperature threshold T

2) Select the Thermistor TH1 (both resistive value at +25°C and beta)

3) Select the value of the resistor R

th

at which the current must start to decrease

threshold

as Rth = TH at T

threshold

Figure 34 Thermal Feedback Network

The thermistor resistance, R

, at a temperature of T degrees Kelvin is given by

T

⎞

⎛

1T1

⎟

⎜

B

−
⎟

⎜

R

⎠

=Te

⎝

RR

RT

Where

R

T

is the thermistor resistance at the reference temperature, TR

R

is the reference temperature, in Kelvin, normally 273 + 25 = 298K (+25°C)

R

B is the “beta” value of the thermistor.

For example,

1) Temperature threshold T

2) TH1 = 10k at +25°C and B = 3900 Æ R

3) R

= RT at T

th

threshold

= 1.8k

= 273 + 70 = 343K (+70°C)

threshold

= 1.8k @ +70°C

T

Over-Temperature Shutdown

The ZXLD1370 incorporates an over-temperature shutdown circuit to protect against damage caused by excessive die temperature. A warning

signal is generated on the STATUS output when die temperature exceeds +125°C nominal and the output is disabled when die temperature

exceeds +150°C nominal. Normal operation resumes when the device cools back down to +125°C.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

29 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

FLAG/STATUS Outputs

The FLAG/STATUS outputs provide a warning of extreme operating or fault conditions. FLAG is an open-drain logic output, which is normally

off, but switches low to indicate that a warning, or fault condition exists. STATUS is a DAC output, which is normally high (4.5V), but switches to

a lower voltage to indicate the nature of the warning/fault.

Conditions monitored, the method of detection and the nominal STATUS output voltage are given in the following table:

Table 2

Warning/Fault Condition

Severity

(Note 17)

Normal operation H 4.5

Supply under-voltage

Output current out of regulation
(Note 18)

Driver stalled with switch ‘on’, or ‘off’
(Note 19)

Device temperature above maximum
recommended operating value

Sense resistor current IRS above
specified maximum

Notes: 17. Severity 1 denotes lowest severity.

18. This warning will be indicated if the output power demand is higher than the available input power; the loop may not be able to maintain regulation.

19. This warning will be indicated if the gate pin stays at the same level for greater than 100µs (e.g. the output transistor cannot pass enough current
to reach the upper switching threshold).

1

2

2

V

2

3

4

Monitored

Parameters

<5.6V

V

AUX

V

<5.6V

IN

outside normal voltage

SHP

range

, or t

OFF

>+125°C

T

J

SENSE

>100µs

>0.32V

t

ON

V

FLAG Nominal STATUS Voltage

L 4.5

L 3.6

L 3.6

L 3.6

L 1.8

L 0.9

VREF

FLAG VOLTAGE

0V

4.5V

Normal

Operations

3.6V

2.7V

1.8V

STATUS VOLTAGE

0.9V

0A

VAUX
UVLO

0

1

Figure 35 Status Levels

- VIN UVLO

- STALL

- OUT of RE G

2

SEVERITY

Over

Temperature

3

Over

Current

4

In the event of more than one fault/warning condition occurring, the higher severity condition will take precedence. E.g. ‘Excessive coil current’

and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin.

>1.7V, V

If V

ADJ

and FLAG are only guaranteed for V

may be greater than the excess coil current threshold in normal operation and an error will be reported. Hence, STATUS

SENSE

<=V

REF

.

ADJ

ZXLD1370

Document number: DS32165 Rev. 5 - 2

30 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Application Information (cont.)

Diagnostic signals should be ignored during the device start –

up for 100s. The device start up sequence will be initiated

both during the first power on of the device or after the PWM

signal is kept low for more than 15ms, initiating the standby

state of the device.

In particular, during the first 100s the diagnostic is signaling

an over-current then an out-of-regulation status. These two

events are due to the charging of the inductor and are not true

fault conditions.

VREF

Product Line o

Diodes Incorporated

ZXLD1370

FLAGSTATUSCoil current

0V

Out of

regulation

Over

Current

225mV /R1

0A

100us

Figure 36 Diagnostic During Start-up

Boosting V

When the input voltage is lower than 8V, the gate voltage will also be lower 8V. This means that depending on the characteristics of the external

MOSFET, the gate voltage may not be enough to fully enhance the power MOSFET. This boosting technique is particularly important when the

output MOSFET is operating at full current, since the boost circuit allows the gate voltage to be higher than 12V. This guarantees that the

MOSFET is fully enhanced reducing both the power dissipation and the risk of thermal runaway of the MOSFET itself. An extra diode D2 and

decoupling capacitor C3 can be used, as shown below in figure 37, to generate a boosted voltage at V

below 8V. This enables the device to operate with full output current when V

threshold MOSFET, the bootstrap circuit is generally not required.

Supply Voltage in Boost and Buck-Boost Mode

AUX

when the input supply voltage at VIN is

AUX

is at the minimum value of 6V. In the case of a low voltage

IN

Figure 37 Bootstrap Circuit for Boost and Buck-Boost Low Voltage Operations

The resistor R2 can be used to limit the current in the bootstrap circuit in order to reduce the impact of the circuit itself on the LED accuracy. The

impact on the LED current is usually a decrease of maximum 5% compared to the nominal current value set by the sense resistor.

The Zener diode D3 is used to limit the voltage on the V

pin to less than 60V.

AUX

Due to the increased number of components and the loss of current accuracy, the bootstrap circuit is recommended only when the system has to

operate continuously in conditions of low input voltage (between 6 and 8V) and high load current. Other circumstances such as low input voltage

at low load current, or transient low input voltage at high current should be evaluated keeping account of the external MOSFET power

dissipation.

ZXLD1370

Document number: DS32165 Rev. 5 - 2

31 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Over-Voltage Protection

The ZXLD1370 is inherently protected against open-circuit load when used in Buck configuration. However care has to be taken with open-

circuit load conditions in Buck-Boost or Boost configurations. This is because in these configurations there is no internal open-circuit protection

mechanism for the external MOSFET. In this case an Over-Voltage-Protection (OVP) network should be provided externally to the MOSFET to

avoid damage due to open circuit conditions. This is shown in figure 38 below, highlighted in the dotted blue box.

The zener voltage is determined according to: Vz = V

If the LEDA voltage exceeds V

on the drain of Q1 falls below V

state.

Care should be taken such that the maximum gate voltage of the Q2 MOSFET is not exceeded.

Take care of the max voltage drop on the Q2 MOSFET gate.

the gate of MOSFET Q2 will rise turning Q2 on. This will pull the PWM pin low and switch off Q1 until the voltage

Z

. If the voltage at LEDA remains above VZ for longer than 20ms then the ZXLD1370 will enter into a shutdown

Z

ZXLD1370

Document number: DS32165 Rev. 5 - 2

Figure 38 OVP circuit

+10% where V

LEDMAX

www.diodes.com

LEDMAX

32 of 39

is maximum LED chain voltage.

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

PCB Layout Considerations

PCB layout is a fundamental activity to get the most of the device in all configurations. In the following section it is possible to find some

important insight to design with the ZXLD1370 both in Buck and Buck-Boost/Boost configurations.

SHP Pin

Inductor, Switch and
Freewheeling Diode

VIN / V

AUX

Decoupling

Figure 39 Circuit Layout

Here are some considerations useful for the PCB layout:

• In order to avoid ringing due to stray inductances, the inductor L1, the anode of D1 and the drain of Q1 should be placed as close

together as possible.

• The shaping capacitor C1 is fundamental for the stability of the control loop. To this end it should be placed no more than 5mm from

the SHP pin.

• Input voltage pins, VIN and VAUX, need to be decoupled. It is recommended to use two ceramic capacitors of 2.2uF, X7R, 100V (C3

and C4). In addition to these capacitors, it is suggested to add two ceramic capacitors of 1uF, X7R, 100V each (C2, C8), as well as a

further decoupling capacitor of 100nF close to the VIN/VAUX pins (C9). VIN and VAUX pins can be short-circuited when the device is

ZXLD1370

Document number: DS32165 Rev. 5 - 2

used in buck mode, or can be driven from a separate supply.

www.diodes.com

33 of 39

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Application Examples
Example 1: 2.8A Buck LED Driver

In this application example, the ZXLD1370 is connected as a buck LED driver. The schematic and parts list are shown below. The LED driver is

able to deliver 2.8A of LED current with an input voltage range of 8V to 24V. In order to achieve high efficiency at high LED current, a Super

Barrier Rectifier (SBR) with a low forward voltage is used as the free wheeling rectifier.

This LED driver is suitable for applications which require high LED current such as LED projector, automatic LED lighting etc.

Figure 40 Application Circuit: 2.8A Buck LED Driver

Table 3: Bill of Material

Ref No. Value Part No. Manufacturer

U1 60V LED driver ZXLD1370 Diodes Inc

Q1 60V MOSFET ZXMN6A09K Diodes Inc

D1 45V 10A SBR SBR10U45SP5 Diodes Inc

L1 33µH 4.2A 744770933 Wurth Electronik

C1 100pF 50V SMD 0805/0603 Generic

C2 1uF 50V X7R SMD1206 Generic

C3 C4 C5 4.7µF 50V X7R SMD1210 Generic
R1 R2 R3 300m 1% SMD1206 Generic

R4 400m 1% SMD1206 Generic
R5 0 SMD 0805/0603 Generic

ZXLD1370

Document number: DS32165 Rev. 5 - 2

www.diodes.com

34 of 39

September 2012

© Diodes Incorporated

A

f

V

Product Line o

Diodes Incorporated

ZXLD1370

Application Information (cont.)

Typical Performance

100%

90%

80%

70%

60%

50%

40%

30%

20%

Efficiency (%)

10%

0%

Efficiency vs Input Voltage

10 12 14 16 18 20 22 24

Input Voltage ( V)

Figure 41 Efficiency

1 LED

2 LED

3000

2500

2000

1500

1000

LED Current (mA)

500

Example 2: 400mA Boost LED Driver

In this application example, the ZXLD1370 is connected as a boost LED driver. The schematic and parts list are shown below. The LED driver

is able to deliver 400mA of LED current into 12 high-brightness LEDs with an input voltage range of 16V to 32V.

The overall high efficiency of 92%+ makes it ideal for applications such as solar LED street lighting and general LED illuminations.

LED Current vs Input Voltage

0

10 12 14 16 18 20 22 24

Input Voltage (V)

Figure 42 Line Regulation

Figure 43 Application Circuit - 400mA Boost LED Driver

Table4. Bill of Material

Ref No.

alue Part No. Manufacturer

U1 60V LED driver ZXLD1370 Diodes Inc
Q1 60V MOSFET ZXMN6A25G Diodes Inc
Q2 60V MOSFET 2N7002A Diodes Inc
D1 100V 3A Schottky PDS3100-13 Diodes Inc
Z1 47V 410mW Zener BZT52C47 Diodes Inc
L1 68µH 2.1A 744771168 Wurth Electronik
C1 100pF 50V SMD 0805/0603 Generic

C3 C9 4.7µF 50V X7R SMD1210 Generic

C2 1µF 50V X7R SMD1206 Generic

R1 R2 560m 1% SMD1206 Generic

R9 R10 33k 1% SMD 0805/0603 Generic

R12 0 SMD 0805/0603 Generic
R15 2.7k SMD 0805/0603 Generic

ZXLD1370

Document number: DS32165 Rev. 5 - 2

35 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Diodes Incorporated

Application Information (cont.)

400mA Boost LED Driver Typical Performance

Product Line o

ZXLD1370

100%

90%

80%

70%

60%

50%

40%

30%

Effici ency

20%

10%

0%

Eff iciency vs Input Volt age

16 18 20 22 24 26 28 30 32

Input Voltage

Figure 44 Efficiency

LED Current

450

400

350

300

250

200

150

100

50

LED Current vs Input Voltage

0

16 18 20 22 24 26 28 30 32

Input Voltage

Figure 45 Line Regulation

Example 3: 700mA Buck-Boost LED Driver

In this application example, the ZXLD1370 is connected as a buck-boost LED driver. The schematic and parts list are shown below. The LED

driver is able to deliver 700mA of LED current into 4 high-brightness LEDs with an input voltage range of 7V to 20V.

Since the Buck-boost LED driver handles an input voltage range from below and above the total LED voltage, the versatile input voltage range

make it ideal for automotive lighting applications.

Figure 46 Application Circuit - 700mA Buck-Boost LED Driver

ZXLD1370

Document number: DS32165 Rev. 5 - 2

36 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Application Information (cont.)

Table 5: Bill of Material

Ref No. Value Part No. Manufacturer

U1 60V LED driver ZXLD1370 Diodes Inc

Q1 60V MOSFET ZXMN6A25G Diodes Inc

Q2 60V MOSFET 2N7002A Diodes Inc

D1 100V 5A Schottky PDS5100-13 Diodes Inc

Z1 47V 410mW Zener BZT52C47 Diodes Inc

L1 22µH 2.1A 744771122 Wurth Electronik

C1 100pF 50V SMD 0805/0603 Generic

C3 C9 4.7µF 50V X7R SMD1210 Generic

C2 1µF 50V X7R SMD1206 Generic

R1 R2 R3 300m 1% SMD1206 Generic

R9 33k 1% SMD 0805/0603 Generic
R10 15k 1% SMD 0805/0603 Generic
R12 0 SMD 0805/0603 Generic
R15 2.7k SMD 0805/0603 Generic

700mA Buck-Boost LED Driver Typical Performance

Product Line o

Diodes Incorporated

ZXLD1370

100%

90%

80%

70%

60%

50%

40%

30%

Efficiency

20%

10%

0%

Efficiency vs Input Voltage

7 8 9 1011121314151617181920

Input Voltage

Figure 47 Efficiency

800

700

600

500

400

300

LED Cur rent

200

100

LED Current vs Input Voltage

0

7 8 9 10 11 12 13 14 15 16 17 18 19 20

Input Voltage

Figure 48 Line Regulation

ZXLD1370

Document number: DS32165 Rev. 5 - 2

37 of 39

www.diodes.com

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

Ordering Information

Part Number Packaging Status

ZXLD1370EST16TC TSSOP-16EP Active

ZXLD1370QESTTC TSSOP-16EP Active 2500 16mm 13”

Where YY is last two digits of year and WW is two digit week number

Part

Marking

ZXLD

1370

YYWW

Reel

Quantity

2500 16mm 13”

Tape Width Reel Size

Package Outline Dimensions (All dimensions in mm.)

Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.

PIN 1

ID MARK

D

X

e

0.25

Gauge Plane

Y

EE1

A2

A

b

A1

θ1

L

Seating Plane

DETAIL

TSSOP-16EP

Dim Min Max Typ

A - 1.20 ­A1 0.025 0.100 -
A2 0.80 1.05 0.90

b 0.19 0.30 -
c 0.09 0.20 -

D 4.90 5.10 5.00

E 6.20 6.60 6.40

E1 4.30 4.50 4.40

e 0.65 BSC

L 0.45 0.75 0.60
L1 1.0 REF
L2 0.65 BSC

X - - 2.997

Y - - 2.997

θ1 0° 8° -

All Dimensions in mm

L1

Suggested Pad Layout

Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.

Y3

X (1 6x)

ZXLD1370

Document number: DS32165 Rev. 5 - 2

X2

Y (1 6x)

Y2

X1

C

Y1

38 of 39

www.diodes.com

Dimensions

C 0.650

X 0.450
X1 3.290
X2 5.000

Y 1.450
Y1 3.290
Y2 4.450
Y3 7.350

Value

(in mm)

September 2012

© Diodes Incorporated

A

f

Product Line o

Diodes Incorporated

ZXLD1370

DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).

Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume
all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated
website, harmless against all damages.

Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel.
Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and
hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or
indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.

Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings
noted herein may also be covered by one or more United States, international or foreign trademarks.

Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:

A. Life support devices or systems are devices or systems which:

1. are intended to implant into the body, or

2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the

labeling can be reasonably expected to result in significant injury to the user.

B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.

Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any
use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its
representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems.

Copyright © 2012, Diodes Incorporated

www.diodes.com

IMPORTANT NOTICE

LIFE SUPPORT

ZXLD1370

Document number: DS32165 Rev. 5 - 2

39 of 39

www.diodes.com

September 2012

© Diodes Incorporated