LM27762: LM27762 does not operate

Hi Vincenzo,

You can order the EVM to get a known working circuit.

Did you connect EN+ and EN- high? Can you send a waveform of the LM27762 VIN, EN+, EN-, and OUT+?

Hi Chris,

sorry for the late response. I have reproduced the schematic on the evaluation board but did not have much luck. Here are the waveforms you asked for

thanks for the help

Vince

Hi Chris,

I was wondering whether you had a chance to look at my problem. Thanks again for the help

Vince

Hi Vince,

I just returned from holiday.

Do you have anything connected on the output?

Just so that I understand, did you order an EVM and retest on this? What did you change?

Hi Chris,

I replicated the schematic provided in the data sheet to obtain a +/-5V output. I tried to test it without load and with a load that would have sunk around 10mA.

Vince

Hi Vince,

In the D/S here, www.ti.com/.../lm27762.pdf, I can't find a schematic for 5Vout.

Can you explain what you changed on the schematic on page 9 of www.ti.com/.../snvu534.pdf

Perhaps a photo of your test setup and EVM would help.

I have few different values compared to the EVM (referring to page 9 of the EVM datasheet)These are the values I changed:

C1: 0.47u

C2: 4.7u

R1/R3: 178k

R2/R4: 56k

In addition, I have two pull down of 10k each on the EN pins.

Here's the pic of a section of the board (I had to desolder the LM27762 to test other parts of the board)

Ah, I think I understand now. You copied the EVM schematic onto your PCB? I thought you had ordered a TI EVM and implemented your schematic on this known working PCB.

I would double check your soldering of the IC to make sure all pins are actually connected.

As well, measure the same voltages (Vin, Vout, EN+) with the tip of the scope probe directly on the IC pin. This measures the actual voltage seen by the IC and overcomes any connection issues anywhere upstream in the circuit.