Diodes ZXLD1362 User Manual

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ZXLD1362

Description

The ZXLD1362 is a continuous mode inductive step-down converter with integrated switch and high side current sense.

It operates from an input supply from 6V to 60V driving single or multiple series connected LEDs efficiently externally adjustable output current up to 1A.

The ZXLD1362 has been qualified to AEC-Q100 Grade 1 enabling operation in ambient temperatures from -40°C to +125°C.

The output current can be adjusted by applying a DC voltage or a PWM waveform. 100.1 adjustment of output current is possible using PWM control.

Applying 0.2V or lower to the ADJ pin turns the output off and switches the device into a low current standby state.

Pin Assignments

Features

• Simple low parts count

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

PWM

• High efficiency (up to 95%)

• Wide input voltage range: 6V to 60V

• Up to 1MHz switching frequency

• Qualified to AEC-Q100 Grade 1

• Typical 2% output current accuracy

• Thermally enhanced TSOT25: 

• Available in Green molding

 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.

82°C/W

JA

60V 1A LED DRIVER WITH AEC-Q100

(Top View)

LX

GND

ADJ

TSOT25

V

IN

I

SENSE

Typical Application Circuit

R

V

IN

ADJ

S

0.1Ω

SET

ZXLD1362

GND

V

IN

24V

C1

4.7µF

C2

100nF

GND

ZXLD1362

Document number: DS33472 Rev. 5 - 2

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L1

68µH

LX

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Pin Description

Name Pin No. Function

LX 1 Drain of NDMOS switch

GND 2 Ground (0V)

Multi-function On/Off and brightness control pin:

• Leave floating for normal operation.(V

ADJ 3

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

• Drive with DC voltage (0.3V < V

o I

OUTnom

= 0.1/RS)

ADJ

= V

ADJ

REF

< 2.5V) to adjust output current from 25% to 200% of I

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

• Soft-start time increases approximately 200µs/nF.

I

SENSE

VIN

4

Connect resistor R (Note: R

SMIN

5 Input voltage (6V to 60V). Decouple to ground with 4.7µF of higher X7R ceramic capacitor close to device.

from this pin to VIN to define nominal average output current I

S

= 0.1 with ADJ pin open circuit)

Block Diagram

V

IN

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ZXLD1362

= 1.25V giving nominal average output current

OUTnom

= 0.1/RS

OUTnom

D1

R

S

L1

``

54 1

GND

C1

4.7µF

ADJ

GND

V

IN

5V

Voltage

regulator

GND

3

R4

50k

D1

1.25V

2

R5

20k

1.35V

R1

0.2V

R2

R3

SENSE

Low voltage

detector

LXI

MN

Figure 1. Block Diagram

ZXLD1362

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ZXLD1362

Absolute Maximum Ratings (Note 4)

Symbol Parameter Rating Unit

VIN

V

SENSE

VLX

V

ADJ

ILX

P

TOT

TST

TJ

MAX

Note: 4 All voltages unless otherwise stated are measured with respect to GND.

5. V

Caution: 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 conditions between maximum recommended operating conditions and absolute maximum ratings is not implied. Device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time.

Input Voltage -0.3 to +65 V

I

Voltage (Note 5)

SENSE

+0.3 to -5 V LX Output Voltage -0.3 to +65 V Adjust Pin Input Voltage -0.3 to +6 V Switch Output Current 1.25 A Power Dissipation

(Refer to Package thermal de-rating curve on page 16)

1 W

Storage Temperature -55 to +150 °C Junction Temperature 150 °C

is measured with respect to VIN.

SENSE

ESD Susceptibility Rating Unit Human Body Model 500 V Machine Model 75 V

Caution: 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.

Thermal Resistance

Symbol Parameter Rating Unit

θ

JA



JB

Junction to Ambient 82 °C/W

Junction to Board 33 °C/W

Recommended Operating Conditions

Symbol Parameter Min Max Units

VIN

ILX

V

ADJ

V

ADJoff

t

ONMIN

f

LXmax

DLX

TA

Notes: 6. 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.

7. 100% brightness corresponds to V proportionally.

8. ZXLD1362 will operate at higher frequencies but accuracy will be affected due to propagation delays.

ZXLD1362

Document number: DS33472 Rev. 5 - 2

Input Voltage Range (Note 6) 6 60 V

Maximum recommended continuous/RMS switch current 1 A External control voltage range on ADJ pin for DC brightness control (Note 7) 0.3 2.5 V

DC voltage on ADJ pin to ensure devices is off 0.25 V Minimum switch on-time 800 ns Recommended maximum operating frequency (Note 8) 625 kHz Duty cycle range 0.01 0.99 Ambient operating temperature range -40 +125 °C

ADJ

= V

ADJ(nom)

= V

. Driving the ADJ pin above V

REF

will increase the V

REF

threshold and output current

SENSE

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ZXLD1362

Electrical Characteristics (Test conditions: 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

tSS

fLX

t

ONmin

t

OFFmin

Notes: 9. Static current of device is approximately 700µA, see Graph, Page 16.

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

ZXLD1362

Document number: DS33472 Rev. 5 - 2

Internal regulator start-up threshold 4.85 V Internal regulator shutdown threshold 4.75 V Quiescent supply current with output off ADJ pin grounded 65 90 µA Quiescent supply current with output switching

(Note 9) Mean current sense threshold voltage

(Defines LED current setting accuracy) Sense threshold hysteresis ±10 %

I

/ΔT Temperature coefficient of V

Resistance between ADJ pin and V

pin input current V

SENSE

Internal reference voltage

REF

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

REF

Continuous LX switch current 1 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 10 5:1

ADJ

Soft start time

Operating frequency (See graphs for more details)

Minimum switch ‘ON’ time LX switch ‘ON’ 130 ns Minimum switch ‘OFF’ time LX switch ‘OFF’ 70 ns

= 24V, TA = +25°C, unless otherwise specified.)

IN

ADJ pin floating, L = 68µH, 3 LEDs, f = 260kHz

Measured on I respect to V

= V

SENSE

IN

SENSE

IN VADJ

-0.1

pin with

= 1.25V

Measured on ADJ pin with pin floating

1.8 mA

95 100 105 mV

4 10 µA

1.25 V

50 ppm/°C

0.3 2.5 V

V

falling

ADJ

rising

V

ADJ

< V

0 < V V

ADJ

> V

REF

+100mV

REF

@ ILX = 1A

PWM frequency <300Hz PWM amplitude = V

REF

0.15 0.2 0.27 V

0.2 0.25 0.3 V

30

10.4

50

14.2

65 18

k

0.5 1.0 

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. Requires

2 ms

external capacitor 22nF. See graphs for more details

ADJ pin floating L = 68µH (0.1V) I

= 1A @ V

OUT

LED

= 3.6V

300 kHz

Driving 3 LEDs

= 1.25/0.3. V

REF

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externally driven to 2.5V, ratio 10:1.

REF

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Device Description

The device, in conjunction with the coil (L1) and current sense resistor (R

Device operation (refer to Figure 1 - Block diagram and Figure 2 Operating waveforms)

), forms a self-oscillating continuous-mode buck converter.

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ZXLD1362

Figure 2. Theoretical Operating Waveforms

Operation can be best understood by assuming that the ADJ pin of the device is unconnected and the voltage on this pin (V

) appears directly at the (+) input of the comparator.

ADJ

When input voltage V

is zero and there is no output from the current sense

and R

S

is first applied, the initial current in L1

IN

circuit. Under this 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

, L1 and the LED(s). The current rises at a rate determined

R

S

and L1 to produce a voltage ramp (V

by V

IN

The supply referred voltage V

is forced across internal

SENSE

to ground, via

IN

SENSE

) across RS.

resistor R1 by the current sense circuit and produces a proportional current in internal resistors R2 and R3. This

comparator. When this reaches the threshold voltage (V the comparator output switches low and MN turns off. The comparator output also drives another NMOS switch, which bypasses internal resistor R3 to provide a controlled amount of hysteresis. The hysteresis is set by R3 to be nominally 10% of

.

V

ADJ

When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to V

. The current decays at a rate

IN

determined by the LED(s) and diode forward voltages to produce a falling voltage at the input of the comparator. When this voltage returns to V

, the comparator output switches

ADJ

high again. This cycle of events repeats, with the comparator input ramping between limits of V

ADJ

± 10%.

ADJ

),

produces a ground referred rising voltage at the (-) input of the

ZXLD1362

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Device Description

Switching Thresholds

With V average V the I I

OUTnom

I

OUTnom

Nominal ripple current is ±10mV/R

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

Actual Operating Waveforms

= V

ADJ

pin with respect to VIN). The average output current

SENSE

is then defined by this voltage and RS according to: = 100mV/RS

V

IN

, the ratios of R1, R2 and R3 define an

REF

switching threshold of 100mV (measured on

SENSE

S

= 15V, RS = 0.1V, L = 100µH Normal operation.

Output Current (Ch1) and LX Voltage (Ch2)

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ZXLD1362

DC or pulse signals to change the V 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 60A and switch leakage is below 5A.

V

= 30V, RS = 0.1V, L = 100µH Normal Operation.

IN

Output Current (Ch1) and LX Voltage (Ch2)

switching threshold

SENSE

V

= 60V, RS = 0.1V, L = 100µH Normal Operation.

IN

Output Current (Ch1) and LX Voltage (Ch2)

ZXLD1362

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Typical Characteristics

1100



1090 1080 1070

1060 1050

1040

Output Current (mA)

1030 1020 1010 1000

0 7040

1 LED

10%

8% 6%

4% 2% 0%

-2%

-4%

Output Current Deviation

-6%

-8%

-10% 0 7040

1 LED

100%

3 LE

ZXLD1362 Output Current

L = 68µH

Supply Voltage (V)

ZXLD1362 Output Current

L = 68µH

Supply Voltage (V)

7 LED5 LE

ZXLD1362 Efficienc

9 LE

L = 68µH

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13 LE

6010 20 30

15 LED13 LED11 LE D9 LED7 LED5 LED3 LED

6010 20 30

15 LE

50

11 LE

ZXLD1362

90%

80%

70%

Efficiency (% )

60%

50%

0 7040

1 LED

ZXLD1362

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15 LED13 LED11 LED9 LED7 LED5 LED3 LED

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Typical Characteristics (cont.)

500

400

300

200

Switching Frequency (kHz)

100

0

0 7040

1 LED

Diodes Incorporated

ZXLD1362 Switching Frequenc

L = 68µH

Supply Voltage (V)

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50

6010 20 30

ZXLD1362

15 LED13 LED11 LE D9 LED7 LED5 LED3 LED

ZXLD1362 Duty Cycle

L = 68µH

100

90 80 70 60 50 40

Du ty Cycle (%)

30 20 10

0

0 7040

1 LED

ZXLD1362

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Supply Voltage (V)

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6010 20 30

15 LED13 LED11 LED9 LED7 LED5 LED3 LED

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