Zxld1360, Application information – Diodes ZXLD1360 User Manual
Page 16
ZXLD1360
ZXLD1360
Document number: DS33471 Rev. 4 - 2
16 of 25
March 2011
© Diodes Incorporated
A Product Line of
Diodes Incorporated
Application Information
(cont.)
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
IN
=15V, R
S
=0.1V, L=33
μH, 100nF on ADJ]
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
μF 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: