zxld1352 Zetex Semiconductors plc., zxld1352 Datasheet - Page 15

• Manufacturer Part Number: zxld1352
• Description: 350ma Led Driver With Internal Switch And Enhanced Pwm Dimming Range
• Manufacturer: Zetex Semiconductors plc.

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 V
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.
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:
Issue 1 - August 2008
© Diodes Incorporated 2008
Manufacturer
Murata
Taiyo Yuden
Kemet
AVX
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15
ZXLD1352
www.diodes.com
www.zetex.com
REF
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