Diodes ZXLD1320 User Manual

ZXLD1320 Buck mode DC-DC converter for LED driving with

1.5A output and current control

Description

The ZXLD1320 is an inductive DC-DC converter, with an internal switch, designed for driving single or multiple LEDs in series up to a total of 1.5A output current.

Applications cover both commercial and automotive environments with input voltages ranging from 4V to 18V. Depending upon supply voltage and external components, this can provide up to 24W of output power.

The device employs a variable 'on' and 'off' time control scheme with adjustable peak switch current limiting and operates in the step-down (Buck) operating mode, offering higher power efficiency and lower system cost than conventional PFM circuitry.

The device includes the DC-DC converter, a high-side current monitor and an NPN switching transistor to provide an integrated solution offering small PCB size, competitive cost/performance, high power efficiency of DC-DC conversion and maximum LED brightness/reliability. More importantly, it retains design flexibility to add customer specific features.

The feedback control circuitry inside the ZXLD1320 provides excellent load and current regulation, resulting in very stable LED current over the full operating voltage and temperature range.

The LED current can be adjusted from 100% down to 10% of the set value by applying a dc voltage to the ADJ pin and down to 1% by applying a PWM signal. An on-chip LED protection circuit also allows output current to be reduced linearly above a predetermined threshold temperature using an external thermistor at the TADJ pin.

External resistors set nominal average LED current and coil peak current independently.

The 'Power-OK' (POK) output flag remains high during normal operation, but switches low if the switch transistor remains on for more than 500

μs. This provides indication of a low battery,

or fault condition. The POK output may be used to drive an LED or the input of an MCU.

The device can be shut down by applying a continuous low level dc voltage to the ADJ pin.

Features

• Step-down LED driver

• 4V to 18V input voltage range

• Up to 1.5A output current

• Typical efficiency

• User-defined thermal control of LED output current using external thermistor

• High output current stability over input voltage and temperature

•12

μA typical standby current

• LED current adjustable from 100% down to 2%

• Adjustable soft-start

• Power 'OK' flag output

• Capable of driving 4 LEDs in series

Note* : Using standard external components as specified under electrical characteristics. Efficiency is dependent upon external component types and values. Higher efficiency is possible with alternative coils.

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> 85%

Applications

• Low voltage halogen lamp replacement with LEDs

• High power LED flashlights

• LED back-up lighting

• General LED lighting

• Automotive lighting

ZXLD1320

Pin connections (top-view) Package view

14-Pin DFN with exposed pad

1.5W @T

Block diagram

Package

4mm x 3mm

0.50mm pitch =70°C

DFN14 Package (bottom view).

45° chamfer denotes Pin 1

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ZXLD1320

Absolute maximum ratings

(Voltages relative to GND unless otherwise stated)

Operating temperature (Top) -40 to 125°C

Storage temperature (Tst) -55 to 150°C

Junction temperature (Tj) -40 to 150°C

Package power dissipation (Ptot) DFN-14 with Exposed Pad: 4mmx3mm, 0.5mm Pitch 1.5W at Tamb = 70°C

DC-DC Converter

Supply voltage (VIN) -0.3V to +18V

POK -0.3V to VIN + 0.3V

ADJ -0.3V to The lower of (+5.0V) or (VIN + 0.3V)

CFB -0.3V to The lower of (+5.0V) or (VIN + 0.3V)

ISENSE -0.3V to The lower of (+5.0V) or (VIN + 0.3V)

TADJ -0.3V to The lower of (+5.0V) or (VIN + 0.3V)

BIAS -0.3V to The lower of (+5.0V) or (VIN + 0.3V)

POK -0.3V to The lower of (+5.0V) or (VIN + 0.3V)

High-Side current monitor

Continuous sense voltage

-0.3V to +5V

(M_VIN – M_LOAD)

Switching NPN transistor

Collector-Base voltage (V

Collector-Emitter voltage (V

Peak pulse current (I

Continuous Collector current (I

)20V

CBO

)20V

CEO

) 3A (Pulse Width = 300µs. Duty Cycle<=2%)

)1.5A

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

Thermal resistance

Junction to ambient (R

) Nominal value

⍜JA

DFN-14 53°C/W

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ZXLD1320

Pin description

Name Pin #Description

ADJ 1 Adjust input

• Leave floating, or connect to VREF to set 100% output current.

• Drive with dc voltage. (50mV<VADJ< VREF) to adjust output current

from 10% to 100% of set value. (DC brightness control mode)

• Drive with low frequency (200Hz) PWM control signal to gate output

‘

on’ and ‘off’ at the PWM frequency. (PWM brightness control mode)

• Drive with low level dc voltage (V

(Standby mode)

BIAS 2 Bias pin for setting base current of internal switch transistor

• Short pin to ground to define maximum base drive current for

output switch (Maximum output current condition)

• Connect resistor (R

) from this pin to ground to reduce base

BIAS

drive current (Reduced output current condition)

CFB 3 Control input/output for feedback control loop

• Connect 10nF capacitor from this pin to ground to provide loop

compensation

POK 4 Power OK flag output

• Pin is high during normal operation.

• Pin switches low if the switch remains on for more than 500µs (nom)

<28mV) to turn off device

ADJ

ISENSE 5 Switch peak current sense pin

• Connect resistor (Rsense) from this pin to ground to define peak

switch current (I

SWPEAK

)=0.05/R

EMITTER1 6

EMITTER2 7

Switch emitters (Connect both pins to top of R

to sense emitter current)

SENSE

COLLECTOR2 8

COLLECTOR1 9

Switch Collectors (Connect both pins to lower side of coil)

M_LOAD 10 Load side input of high side current monitor.

Connect to sensing resistor RM.

N/C 11 Not connected locally

VIN 12 Positive supply to device (4-18V) and sensing resistor R

• Decouple to ground with capacitor close to device

• nominal average output (LED) current = 0.1/R

TADJ 13 Temperature Adjust input for LED thermal compensation

• Connect thermistor/resistor network to this pin to reduce output

current above a preset temperature threshold.

• Connect to VREF to disable thermal compensation function

(see section on temperature control for details)

VREF 14 Internal 0.5V reference voltage output

Exposed Pad 15 Connect to Ground (0V)

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ZXLD1320

Electrical characteristics (Test conditions: VIN = 4V, T

= 25°C unless otherwise stated

AMB

(a)

DC-DC converter supply parameters

Symbol Parameter Conditions Min Typ Max Units

Iq Quiescent current Measured into VIN

Supply voltage Normal operation 4.0 18 V

1.5 mA ADJ pin floating. (Excluding switch base current).

STBY

Standby current

Measured into VIN.

12 20 µA

ADJ pin grounded

REF

Internal reference voltage ADJ pin floating

480 500 520 mV

2.0V<VIN<18V

CO(REF)

NOTES:

(a) Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified from -40°C to

+125

Internal reference temperature coefficient.

Care guaranteed by design, characterisation and process control.

50 ppm

DC-DC converter input parameters

Symbol Parameter Conditions Min Typ Max Units

SENSE

Peak switch current sense voltage

Measured on I pin CFB pin at 0V

Sense input current Measured into

ISENSE

with pin at

SENSE

45 55 65 mV

-15 -7 -1 µA

0V. CFB pin at 0V

Control loop compensation

10 nF

capacitor

ADJ

External dc control voltage applied to ADJ pin to adjust

DC brightness control mode

50 500 mV

output current

ADJ(th)

Switching threshold of ADJ pin Standby state to

26 28 30 mV

normal operation

TCO

(VADJ)

Temperature coefficient of

+0.3 %/K

VADJ(th)

ADJ

Internal resistor between VREF

VADJ<500mV 100 kΩ

and ADJ

VAD J( cl mp )

Internal clamp voltage on ADJ pin

100µA injected into ADJ pin

575 mV

)

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ZXLD1320

DC-DC converter output parameters

Symbol Parameter Conditions Min Typ Max Units

Toff(100) Discharge pulse width 100% Output current 0.7 1.2 1.7 µs

Toff(10) Discharge pulse width 10% Output current 4 8 12 µs

LXmax

Maximum operating

600 KHz

frequency

OH(POK)

OL(POK)

POK flag high level output voltage

POK flag low level output

4V<VIN<18V

2VINV

Output sourcing 0.3µA

Output sinking 1mA 0 0.4 V

voltage

(POK)

POK assertion delay time

Switch permanently on

300 500 700 µs

Switching NPN transistor

Symbol Parameter Conditions Min Typ Max Units

SW Average continuous switch

(b)

BON(max)

current

Maximum base current into switch transistor from internal

(c)

BON

drive circuit

Base current into switch

4V<VIN<18V

30 50 70 mA

BIAS pin at 0V

= 1680Ω 10 mA

BIAS

1.5 A

transistor using external resistor (R

) from BIAS pin

BASE

to ground

(BR)CE

Collector-Emitter breakdown

IC=10µA 20 V

voltage

CE(sat)

Collector-Emitter saturation

IC=0.1A, IB=10mA

voltage

=2A, IB=50mA

Static forward current transfer ratio

OBO

Output capacitance VCB=10V,f=1MHz 64 pF

t(on) Turn-on time Ic=0 to I

t(off) Turn-off time I

NOTES:

(b) Measured under pulse conditions. (c) This current is measured via the collectors and emitters of the switch with these connected to ground (0V) (d) Measured under pulse conditions. Peak Current = Ic

IC=200mA, VCE=2V

=2A, VCE=2V

=2A

=10V

=2A to Ic<100µA 28 ns

(d)

120

209 116

30 ns

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