ZXLD1321 datasheet(4/20 Pages) ZETEX

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ZXLD1321

Issue 1 - January 2008

www.zetex.com

Pin description

Name

Pin # Description

ADJ

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 (VADJ<28mV) to turn off device

(Standby mode)

BIAS

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 (RBIAS) from this pin to ground to reduce base

drive current (Reduced output current condition)

CFB

Compensation point

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

compensation

N/C

No connection to this pin (open circuit)

ISENSE

Switch peak current sense pin

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

switch current (ISWPEAK)=VSENSE/RSENSE

EMITTER

6, 7

Switch emitters (connect both pins to top of RSENSE to sense emitter current)

COLLECTOR

8, 9

Switch collectors (connect both pins to lower side of coil)

M_LOAD

Load side input of high side current monitor

M_VIN

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/RM

VIN

Positive supply to device (1.2-12V)

• Decouple to ground with capacitor close to device

TADJ

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

Internal 0.5V reference voltage output

Exposed pad

Connect to ground (0V)

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