zxld1360 Zetex Semiconductors plc., zxld1360 Datasheet - Page 18

• Manufacturer Part Number: zxld1360
• Description: 1a Led Driver With Internal Switch
• Manufacturer: Zetex Semiconductors plc.

This time has been extended on the trace below by adding a 100nF ceramic capacitor which gives
a soft start time of 40 milliseconds approximately.
Actual operating waveforms [V
Soft-start operation. Output current (Ch2) and LX voltage (Ch1)
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 4.7 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 suitable Murata capacitor would be GRM42-2X7R475K-50.
The following web sites are useful when finding alternatives:
Issue 1 - March 2007
© Zetex Semiconductors plc 2007
www.murata.com
www.t-yuden.com
www.kemet.com
www.avxcorp.com
IN
=15V, R
S
=0.1 , L=33µH ,100nF on ADJ]
18
ZXLD1360
www.zetex.com