Diodes ZXLD1321 User Manual

ZXLD1321 Boost mode DC-DC converter for LED driving with 1A output and current control

Description

The ZXLD1321 is an inductive DC-DC converter, with an internal switch, designed for driving single or multiple LEDs in series up to a total of 1A output current.

Applications cover commercial environments with input voltages ranging from 1.2V to 12V.

The device employs a variable 'on' and 'off' time control scheme with adjustable peak switch current limiting and supports step-up (Boost) mode and self-powering Bootstrap operating modes, 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 ZXLD1321 provides excellent load and current regulation, resulting in very stable LED current over the useful life of the battery and over the full operating 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 to the ADJ pin. An onchip 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 device can be shut down by applying a continuous low level dc voltage to the ADJ pin.

Features

• 1.2V to 12V Input voltage range

• Up to 1A output current

• Typical efficiency# >85%

• Bootstrap operation enables input voltage down to 1V

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

• High output current stability over input voltage and temperature

• 12µA typical standby current

• LED current adjustable from 100% down to 2%

• Adjustable soft-start

• Drives up to 5 white 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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Applications

• High power LED flashlights

• LED back-up lighting

• General LED lighting

• Emergency lighting

ZXLD1321

Pin connections (top-view) Package view

14-Pin DFN with exposed pad

1.5W @TA=70°C

Block diagram

Package

4mm x 3mm

0.50mm pitch

DFN14 package (bottom view).

45° chamfer denotes Pin 1

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ZXLD1321

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 +12V

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)

High-side current monitor

Monitor supply voltage (M_VIN) -0.3V to +18V

Continuous sense voltage

-0.3V to +5V

(M_VIN – M_LOAD)

Switching NPN transistor

Collector-Base voltage (V

Collector-Emitter voltage (V

) 18V

CBO

) 18V

CEO

Peak pulse current (ICM) 3A (Pulse width = 300µs. Duty cycle<=2%)

Continuous Collector current (IC) 2A

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 case (R

) Nominal value

UJC

DFN-14 26.3°C/W

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ZXLD1321

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 ‘ control mode)

• Drive with low level dc voltage (VADJ<28mV) to turn off device (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 drive current (Reduced output current condition)

CFB 3 Compensation point

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

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

) from this pin to ground to reduce base

BIAS

N/C 4 No connection to this pin (open circuit)

ISENSE 5 Switch peak current sense pin

EMITTER 6, 7

• Connect resistor (R switch current (ISW

Switch emitters (connect both pins to top of R

) from this pin to ground to define peak

SENSE

)=V

PEAK

SENSE/RSENSE

SENSE

to sense emitter current)

COLLECTOR 8, 9 Switch collectors (connect both pins to lower side of coil)

M_LOAD 10 Load side input of high side current monitor

M_VIN 11 Input supply to high side current monitor

• Connect to output voltage (cathode of Schottky)

• Connect resistor (RM) between M_LOAD and M_VIN to define nominal average output (LED) current of 0.1/R

VIN 12 Positive supply to device (1.2-12V)

• Decouple to ground with capacitor close to device

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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ZXLD1321

Electrical characteristics (Test conditions: VIN = 3V, T

= 25°C unless otherwise stated

AMB

(a)

DC-DC converter supply parameters

Symbol Parameter Conditions Min Typ Max Units

VIN(Start) Supply voltage for start-up

UV-

Supply voltage Normal operation 2.0 12 V

(b)

Under-voltage detection threshold

Start-up mode 1.2 2.4 V

VIN falling 1.8 V

Normal operation to start-up mode

UV+

Under-voltage detection threshold

VIN rising 2.2 V

Start-up mode to normal operation

Iq Quiescent current Measured into VIN

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

TCO

(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°C are guaranteed by design, characterisation and process control.

(b) Between 1.2V and 2.2V the device will run in the Low Voltage Startup Mode (for details refer to section "Low Voltage Operation")

Internal reference temperature coefficient.

50 ppm

DC-DC converter input parameters

)

Symbol Parameter Conditions Min Typ Max Units

SENSE

(SU)

Peak switch current sense voltage

Peak switch current sense voltage in start-up mode

Measured on ISENSE pin CFB pin at 0V

Measured on ISENSE pin.

45 55 65 mV

10.5 mV

Start-up mode VIN=1.2V

SENSE

Sense input current Measured into

-15 -7 -1 µA ISENSE with pin at 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)

TCO

(VADJ)

Switching threshold of ADJ pin

Temperature coefficient of

Standby state to normal operation

26 28 30 mV

+0.3 %/K

VADJ(th)

ADJ

Internal resistor between

VADJ<500mV 100 kΩ

VREF and ADJ

VADJ(clmp)

Clamp voltage on ADJ pin 100µA injected into

575 mV

ADJ pin

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ZXLD1321

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

Switching frequency in start-

VIN=1.2V 50 KHz

up mode

Switching NPN transistor

Symbol Parameter Conditions Min Typ Max Units

ISW Average continuous switch

(c)

BON(max)

current

Maximum base current into switch transistor from internal

(d)

BON

drive circuit

Base current into switch

2V<VIN<18V

30 50 70 mA

BIAS pin at 0V

= 1680Ω 10 mA

BIAS

2 A

transistor using external resistor (R

) from BIAS pin

BASE

to ground

(BR)CEO

Collector-Emitter breakdown

IC=10µA 20 V

voltage

CE(sat)

Collector-Emitter saturation

IC=0.1A, IB=10mA

voltage

=2A, IB=50mA

(e)

120

Static forward current transfer ratio

OBO

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

t(on) Turn-on time Ic=0 to IC=2A

IC=200mA, VCE=2V IC=2A, VCE=2V

209 116

30 ns

VIN=10V

t(off) Turn-off time IC=2A to Ic<100µA 28 ns

NOTES:

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

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