Part Number:TPS61169
Hi,
I'm trying to design LED driver based on the TPS61169 chip. I need to drive 7x SFH 5240S IR LEDs (Vf is about 3V) with 50mA current (~21V @ 50mA). Power supply is from 3V to 4.5V.
Together with TPS61169 I am using:
- 10uH LPS4018-103MRB inductor
- NSR0240 schottky diode
- 4.7uF ceremic capacitor on input and output
- 3.9ohm shunt resistor in feedback
The problem is that, driver starts to work only above 5V. When below 5V, it boosts the voltage to the needed level, bet then switches off and this repeats. I have included a picture from scope where I monitor voltage on feedback pin.
What could be the problem?
Thank you!
/Janis
