I'm trying to build a buck circuit to power an ESP-2866 and neopixel LEDs for a project. I'm using the fixed 5 V version. The LEDs are powered from 5 V and there's a 3.3 V linear converter downstream that delivers power to the micro.
I've followed the datasheet parameters and also simulated the circuit with TI's Webench, but I can't get it to work. I get no output from the LM2596 and both the IC and the inductor get extremely hot. The parameters used are:
- Input: 10 V nominal (12 V max, 9 V min)
- Output: 3 A max (but this is just peak, the LEDs are off most of the time)
This is my schematic:
And this is the layout of my PCB (top and bottom):
Summarized BOM (all recommended by Webench design):
- L1: Coilcraft MSS1210 AEC-Q200 33μH 20% 5.9A
- C_IN1: 16V 39μF ESR 27mΩ
- U5: LM2596SX-5.0/NOPB
- D_REG: 200V 10A 900mV @ 10A DPAK Schottky
- C_OUT1: 4.7μF ±10% 10V 1400mΩ @ 100kHz -55°C ~ +125°C CASE-A_1206 Tantalum
- U4 and C8 are the 3.3V linear converter and its input filter cap.
(Side question: does it make any sense to have a filter cap after an output filter cap? And should I isolate the buck with a diode here?)
I've tried to have thick traces and keep them short. The LM2596 ICs, the caps and coils were from Mouser. I've tried replacing them in case I fried them soldering or testing, but nothing. I even tried a different LM2596, one from XLSEMI in case I got a batch of bad ones and still no dice.
I don't have any shorts (that I've been able to find). Pin 1 receives 12 V fine (12.3 V in fact, a bit high but within tollerance?), but the output on pin 4 is 0.3 V. I don't know what else to test or if it's just an error in my layout.
I'd appreciate any pointers or help.