Diodes ZXLD1356, ZXLD1356Q User Manual

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ZXLD1356/ ZXLD1356Q

60V 550mA LED DRIVER and AUTOMOTIVE GRADE

Description

The ZXLD1356 is a continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The device operates from an input supply between 6V and 60V and provides an externally adjustable output current of up to 550mA. Depending upon supply voltage and external components, this can provide up to 30 watts of output power.

The ZXLD1356 has been qualified to AECQ100 Grade 1 enabling operation in ambient temperatures from -40°C to +125°C

Output current can be adjusted above, or below the set value, by applying an external control signal to the 'ADJ' pin. Enhanced output current dimming can be achieved by applying a PWM signal to the ‘ADJ’ pin.

Features

• Typically better than 0.8% output current accuracy

• Simple and with low part count

• Single pin on/off and brightness control using DC voltage or PWM

• PWM resolution up to 1000:1

• High efficiency (up to 97%)

• Wide input voltage range: 6V to 60V

• Inherent open-circuit LED protection

• Available in thermally enhanced packages

 V-DFN3030-6 θ  TSOT25 θ

• 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)

• ZXLD1356QET5TA Automotive Grade qualified to AEC-Q100 Grade 1

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.

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ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

44°C/W

82°C/W

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Pin Assignments

(TOP VIEW)

1

LX

2

GND

3

ADJ

(TOP VIEW)

LX

1 2

GND

34

ADJ

V-DFN3030-6

Applications

• Low Voltage Halogen Replacement LEDs

• Automotive Lighting

• Low Voltage Industrial Lighting

• LED Back-Up Lighting

• Illuminated Signs

• Emergency Lighting

• SELV Lighting

• Refrigeration Lights

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TSOT25

6 5

5

4

V

GND

I

SENSE

V

IN

I

SENSE

IN

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Typical Applications Circuit

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ZXLD1356/ ZXLD1356Q

D1

VIN(24V)

Rs

0.36V

L1

4.7µFC1

100nF

V

ADJ

IN

I

SENSE

ZXLD1356

GND

LX

GND

Pin Descriptions

Name

LX 1 1 Drain of NDMOS switch

GND 2 2, 5 Ground (0V)

ADJ 3 3

I

SENSE

VIN

Pad — Pad

TSOT25 V-DFN3030-6

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

Number

Multi-function On/Off and brightness control pin:

• Leave floating for normal operation.(V

• Drive to voltage below 0.2V to turn off output current

• Drive with DC voltage (0.3V<V

• Connect a capacitor from this pin to ground to define soft-start time.

4 4

5 6

Connect resistor R (Note: R Input voltage (6V to 60V). Decouple to ground with 4.7µF of higher X7R ceramic capacitor close

to device Exposed pad (EP) - connected to device substrate.

To improve thermal impedance of package the EP must be connected to power ground but should not be used as the 0V (GND) current path. It can be left floating but must not be connected to any other voltage other than 0V.

current o I

I

OUTnom

Soft-start time is approx.0.2ms/nF

SMIN

= 0.2V/RS)

OUTnom

ADJ

from this to VIN to define nominal average output current I

S

=0.36V with ADJ pin open circuit)

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Function

= V

ADJ

<2.5V) to adjust output current from 24% to 200% of

= 1.25V giving nominal average output

REF

= 0.2/RS

OUTnom

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Functional Block Diagram

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ZXLD1356/ ZXLD1356Q

R

D1

S

L1

I

SENSE

-

+

-

+

Low voltage

detector

LX

MN

C1

4.7μF

Gnd

Adj

V

54 1

IN

Voltage

regulator

5V

R1

0.2V

-

+

3

R5

50K

1.25V

R4

20K

D1

600KHz

1.35V

R2

-

+

R3

2

Figure 1. Block Diagram – Pin Connections Shown for TSOT25 Package

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

Symbol Parameter Rating Unit

VIN

V

SENSE

VLX

V

ILX

P

TOT

TST

TJ

These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure. Operation at the absolute maximum rating for extended periods may reduce device reliability.

Input Voltage

I

SENSE

Voltage

(measured with respect to V LX Output Voltage Adjust Pin Input Voltage -0.3 to +6.0 V

ADJ

Switch Output Current 0.65 A Power Dissipation

(Refer to package thermal de-rating curve on page 25)

TSOT25 1

V-DFN3030-6 1.8 Storage Temperature -55 to +150 °C Junction Temperature 150 °C

MAX

ESD Susceptibility Rating Unit Human Body Model 500 V Charged Device Model >1000 V Machine Model <100 V

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. The human body model is a 100pF capacitor discharge through a 1.5k resistor pin. The machine model is a 200pF capacitor discharged directly into each pin.

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

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-0.3 to +60

(65V for 0.5 sec)

+0.3 to -5.0

-0.3 to +60

(65V for 0.5 sec)

)

IN

W

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Thermal Resistance

Symbol Parameter







Recommended Operating Conditions (@T

Symbol Parameter Min Max Units

VIN

t

OFFMIN

t

ONMIN

f

LX max

DLX TOP

Notes: 4. VIN > 16V to fully enhance output transistor. Otherwise out current must be derated - see graphs. Operation at low supply may cause excessive heating due to increased on-resistance. Tested at 7V guaranteed for 6V by design.

5. ZXLD1356 will operate at higher frequencies but accuracy will be affected due to propagation delays.

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

Junction to Ambient 82

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Junction to Board 33

JB

Junction to Case —

JC

= +25°C, unless otherwise specified.)

A

Input voltage (Note 4) 6 60 V Minimum switch off-time 800 ns Minimum switch on-time 800 ns Recommended maximum operating frequency (Note 5) 625 kHz Duty cycle range 0.01 0.99 Operating temperature range -40 +125 °C

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TSOT25 V-DFN3030-6

Rating Unit

44 — 14

°C/W °C/W °C/W

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Electrical Characteristics (V

Symbol Parameter Condition Min Typ Max Unit

VSU VSD

I

INQoff

I

INQon

V

SENSE

V

SENSEHYS

I

SENSE

V

REF

ΔV

REF

V

ADJ

V

ADJoff

V

ADJon

R

ADJ

I

LXmean

RLX

I

LX(leak)

D

PWM(LF)

DC

ADJ

tSS

fLX

f

LXmax

Notes: 6. Static current of device is approximately 700 µA, see Graph, Page 17.

7. 100% brightness corresponds to V proportionally.

8. Ratio of maximum brightness to minimum brightness before shutdown V

Internal regulator start-up threshold 4.85 5.2 V Internal regulator shutdown threshold 4.40 4.75 V Quiescent supply current with output off ADJ pin grounded 65 108 µA

Quiescent supply current with output switching (Note 6)

Mean current sense threshold voltage (Defines LED current setting accuracy)

Sense threshold hysteresis ±15 %

I

pin input current V

SENSE

Internal reference voltage

/ΔT Temperature coefficient of V

External control voltage range on ADJ pin for DC brightness control (Note 7)

DC voltage on ADJ pin to switch device from

active (on) state to quiescent (off) state

DC voltage on ADJ pin to switch device from

quiescent (off) state to active (on) state

Resistance between ADJ pin and V

Continuous LX switch current 0.55 A LX switch ‘On’ resistance LX switch leakage current 5 µA Duty cycle range of PWM signal applied to ADJ

pin during low frequency PWM dimming mode

Brightness control range 1000:1

(*)

DC Brightness control range Note 8 5:1

Start up time (See graphs for more details)

Operating frequency (See graphs for more details)

Recommended maximum operating frequency 500 kHz

= 24V, @T

IN

REF

= V

ADJ

AMB

0< V

REF

= V

ADJ(nom)

= +25°C, unless otherwise specified.)

ADJ pin floating, L = 68mH, 3 LEDsf = 360kHz

Measured on I to V

SENSE

IN VADJ

= V

= 1.25V; V

IN

pin with respect

SENSE

-0.2

= 18V

IN

Measured on ADJ pin with pin floating

1.6 mA

195 200 205 mV

4 10 µA

1.25 V

50 ppm/°C

0.3 2.5 V

V

falling

ADJ

V

rising

ADJ

< V

, V

> V

+100mV

REF

@ I

ADJ

= 0.55A

LX

REF

ADJ

PWM frequency <300Hz PWM amplitude = V

REF

0.15 0.20 0.27 V

0.2 0.25 0.3 V 30

10.4

50

14.2

65

18.0

k

0.5 0.75 

0.001 1

Measured on ADJ pin

Time taken for output current to reach 90% of final value after voltage on ADJ pin has risen above 0.3V.

2 ms

Requires external capacitor 22nF. ADJ pin floating L= 68mH (0.36V)

= 0.55A @ V

I

OUT

LED

= 3.6V

360 kHz

Driving 3 LEDs

. Driving the ADJ pin above V

REF

=1.25/0.25. V

REF

will increase the V

REF

externally driven to 2.5V, ratio 10.1.

REF

SENSE

. threshold and output current

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

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Device Description

The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a self-oscillating continuous-mode buck converter. Device operation (refer to Figure 1 - Block diagram and Figure 2 operating waveforms)

LX voltage

V

IN

SENSE voltage

Coil current

Comparator input voltage

Comparator output

0V

V

IN

0V

0.15V

ADJ

V

ADJ

5V

0V

Toff Ton

170mV

200mV230mV

V

SENSE-

V

SENSE+

I

+15%

OUTnom

I

OUTnom

-15%

I

OUTnom

0.15V

ADJ

Operation can be best understood by assuming that the ADJ pin of the device is unconnected and the voltage on this pin (V at the (+) input of the comparator.

When input voltage V

is first applied, the initial current in L1 and RS is zero and there is no output from the current sense circuit. Under this

IN

condition, the (-) input to the comparator is at ground and its output is high. This turns MN on and switches the LX pin low, causing current to flow from V

to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN and L1 to produce a voltage ramp (V

IN

. The supply referred voltage V

R

S

is forced across internal resistor R1 by the current sense circuit and produces a proportional current in

SENSE

internal resistors R2 and R3. This produces a ground referred rising voltage at the (-) input of the comparator. When this reaches the threshold voltage (V

), the comparator output switches low and MN turns off. The comparator output also drives another NM OS switch, which bypasses

ADJ

internal resistor R3 to provide a controlled amount of hysteresis. The hysteresis is set by R3 to be nominally 15% of V

When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to V and diode forward voltages to produce a falling voltage at the input of the comparator. When this voltage returns to V switches high again. This cycle of events repeats, with the comparator input ramping between limits of V

Switching Thresholds

With V to V

I

OUTnom

Nominal ripple current is ±30mV/R

= V

ADJ

). The average output current I

IN

= 200mV/R

, the ratios of R1, R2 and R3 define an average V

REF

S

OUTnom

S

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

Figure 2. Theoretical Operating Waveforms

. The current decays at a rate determined by the LED(s)

IN

switching threshold of 200mV (measured on the I

SENSE

is then defined by this voltage and RS according to:

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ADJ

± 15%.

) appears directly

ADJ

SENSE

.

ADJ

, the comparator output

ADJ

pin with respect

SENSE

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Device Description (cont.)

Adjusting Output Current

The device contains a low pass filter between the ADJ pin and the threshold comparator and an internal current limiting resistor (50k nom) between ADJ and the internal reference voltage. This allows the ADJ pin to be overdriven with either DC or pulse signals to change the V switching threshold and adjust the output current.

Details of the different modes of adjusting output current are given in the applications section.

Output Shutdown

The output of the low pass filter drives the shutdown circuit. When the input voltage to this circuit falls below the threshold (0.2V nom.), the internal regulator and the output switch are turned off. The voltage reference remains powered during shutdown to provide the bias current for the shutdown circuit. Quiescent supply current during shutdown is nominally 60µA and switch leakage is below 5µA.

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

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Actual Operating Waveforms [V

Normal operation. Output current (Ch3) and LX voltage (Ch2)

Actual Operating Waveforms [V

Normal operation. Output current (Ch3) and LX voltage (Ch2)

Actual Operating Waveforms [V

Normal operation. Output current (Ch3) and LX voltage (Ch2)

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

= 15V, RS = 0.36V, L = 68µH]

IN

= 30V, RS = 0.36V, L = 68µH]

IN

= 60V, RS = 0.36V, L = 68µH]

IN

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Typical Operating Conditions

0.640



0.620

0.600

0.580

0.560

Outp ut Current (A)

0.540

0.520

0.500 040

1 LED

ZXLD1 356 Output Current

L = 68µH

Supply Voltage (V)

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50

6010 20 30

15 LEDs13 LEDs11 LEDs9 LEDs7 LEDs5 LEDs3 LEDs

ZXLD1356 Output Current Deviation (Normalized)

10%

8% 6% 4% 2%

0%

-2%

-4%

Output Current Deviation (%)

-6%

-8%

-10% 040

1 LED

100%

95% 90% 85% 80%

75% 70%

Effici ency (%)

65% 60% 55% 50%

040

1 LED

ZXLD1356/ ZXLD1356Q

Document number: DS33470 Rev. 4 - 2

L = 68µH

Supply Voltage (V)

ZXLD1356 Efficienc

L = 68µH

Supply Voltage (V)

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50

6010 20 30

15 LEDs13 LEDs11 LE Ds9 LEDs7 LEDs5 LEDs3 LEDs

6010 20 30

15 LEDs13 LEDs11 LEDs9 LEDs7 LEDs5 LEDs3 LEDs

October 2012