ZXLD1352 查看數據表（PDF） - Zetex => Diodes

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产品描述 (功能)

生产厂家

ZXLD1352

350mA LED driver with internal switch and enhanced PWM dimming range

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ZXLD1352

Shutdown mode

Taking the ADJ pin to a voltage below 0.2V will turn off the output and supply current will fall to

a low standby level of 20µA nominal.

Note that the ADJ pin is not a logic input. Taking the ADJ pin to a voltage above VREF will increase

output current above the 100% nominal average value. (See graphs for details).

Soft-start

An external capacitor from the ADJ pin to ground will provide soft-start delay, by increasing the

time taken for the voltage on this pin to rise to the turn-on threshold and by slowing down the

rate of rise of the control voltage at the input of the comparator. The graph below shows the

variation of soft-start time for different values of capacitor.

Soft Start Time vs Capacitance from ADJ pin to Ground

10

8

6

4

2

0

0

5

10

15

20

25

Capacitance (nF)

Inherent open-circuit LED protection

If the connection to the LED(s) is open-circuited, the coil is isolated from the LX pin of the chip, so

the device will not be damaged, unlike in many boost converters, where the back EMF may

damage the internal switch by forcing the drain above its breakdown voltage.

Capacitor selection

A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in

series with the supply source impedance and lowers overall efficiency. This capacitor has to

supply the relatively high peak current to the coil and smooth the current ripple on the input

supply. A minimum value of 1␮F is acceptable if the input source is close to the device, but higher

values will improve performance at lower input voltages, especially when the source impedance

is high. The input capacitor should be placed as close as possible to the IC.

For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better

dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this

application and should NOT be used.

A table of recommended manufacturers is provided below:

Manufacturer

Murata

Taiyo Yuden

Kemet

AVX

Website

www.murata.com

www.t-yuden.com

www.kemet.com

www.avxcorp.com

Issue 1 - August 2008

15

© Diodes Incorporated 2008

www.zetex.com

www.diodes.com

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