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I'm considering using a tps61165 led driver for an LCD backlight. While I know it is far from recommended, I quickly breadboarded the typical application circuit using TH components that match the recommended SMD parts as much as possible, and used a SOT to DIP adapter for the IC.

In my case I have to go from 5V to 12.8V @ 40mA. (2x4 LEDs). For some reason the circuit works fine when I take out the C4 4.7uF input cap. When I do use it, I only get a really low output current, barely enough to light up the LEDs.

led driver circuit

Why could this be the case?

-- edit --

the breadboard

Notes:

  • C4 is on the far right in this picture where I put it.
  • R4 and R5 are not in this picture.
  • R1 is 2x10R
  • L1 is a Bourns RLB0712-100K
  • D1 is an 1N5817

While I was editting the post to add the breakout picture, I noticed something new: When I enable power without C4 present, it will start up and light the LEDs at the desired power. Then I can add C4 while it is running and it will keep running and light the LEDs even brighter. But when I power up the circuit with C4 already there, it will get stuck in a low power output.

The location of adding C4 (after the circuit is running) also seems to matter. When I put it far away from the IC, it will increase brightness, but when I add it close to the IC when the system runs, it will shut down the cicruit.

Also when I power up the circuit with C4 present, I will get a weak constant output current when C4 is far away from the IC, but I'll only get a short blink once when I put it as close to the IC as the breadboard permits.

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  • \$\begingroup\$ Could you post a picture of your breadboarded prototype? Componet placement / wire length issues could perhaps be deduced from it. \$\endgroup\$ – crj11 Mar 15 '18 at 14:22
  • \$\begingroup\$ picture and "BOM" added as well as an important new condition. \$\endgroup\$ – Genoil Mar 15 '18 at 14:50
  • \$\begingroup\$ Did you try it with C4 directly across pins 1 to 4 of the chip? \$\endgroup\$ – crj11 Mar 15 '18 at 14:54
  • \$\begingroup\$ yes see the additonal notes I just made to the post. \$\endgroup\$ – Genoil Mar 15 '18 at 14:59
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    \$\begingroup\$ You also might try minimizing the D1/C5 loop by grounding C5 directly on pin 4 of the chip. You can make the D1/C5 connection in the row adjacent to the chip. \$\endgroup\$ – crj11 Mar 15 '18 at 15:34
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You should try to minimize the area of the input and output current loops. The the D1/C5 loop can be reduced by grounding C5 directly on pin 4 of the chip. You can make the D1/C5 connection in the row adjacent to the chip.

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