NPM1100 PMIC damage when powering external TLV320AIC3104 codec from NRF5340 Audio DK 1.8V rail

[Falguni]

I am using the NRF5340 Audio DK, and the onboard PMIC is the NPM1100.
I am not using the onboard audio codec of the DK. Instead, I am powering an external audio codec module (TLV320AIC3104) which requires 3.3 V and 1.8 V supplies.

The 1.8 V supply for the external codec is taken directly from the NPM1100 VOUT_1V8 rail on the NRF5340 Audio DK.

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Problem Faced:
I have damaged the PMIC on three different DK boards after connecting the external codec’s 1.8 V input to the NPM1100 1.8 V rail.

Observed behaviour of damaged boards:

1. Board 1:
   The NPM1100 changed its mode configuration from Hysteretic mode to PWM mode without any user configuration change. PMIC does not behave normally afterward.

2. Board 2 & 3:
   The NPM1100 does not provide a stable 1.8 V output anymore (behaves as malfunctioning or partially damaged).

However:

• When I power the external codec from the AP7346D-3318 regulator present on the DK instead of the NPM1100, there is no failure, and everything works normally.

• The AP7346D regulator is also a 1.8 V device with similar current capability and does not get damaged.

This makes me suspect some form of reverse current, back-feeding, or startup-sequence issue specifically affecting the NPM1100 but not the AP7346D.

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What I Need to Understand:

1. Why is the NPM1100 PMIC getting damaged when powering an external codec?

2. Does the NPM1100 have limited reverse-current protection on the 1.8 V rail?

3. Can the external codec board cause back-feeding into the PMIC during power-up/power-down?

4. Why does the AP7346D-3318 regulator survive the same conditions without any failure, while the PMIC does not?

5. Does the NPM1100 require external protection (Schottky diode or load switch) when its output is connected to external capacitive or powered loads?

[Kazi Afroza Sultana]

Hello,

1. This is difficult to say based on just this information. If you have some current/voltage waveform of the startup and schematic can share with us. That would be helpful.

2. No.

3. Yes, that is possible. In hysteretic mode, the buck converter can not sink current, so if there is any backfeeding to the output of the buck the voltage starts rising.

4. We have not designed AP7346D-3318 regulator. But we are comparing LDO to buck, so we don't think this is comparable.

5. No.

The nPM1100’s 1.8 V rail is not intended for significant external loading beyond 150 mA. Overloading or improper connection of external loads can damage the PMIC.

[Falguni]

Will you please explain  how backfeeding can damge my pmic  , also tell that how backfeeding will be there if my source 1v8 is supplied from pmic output to the tlv320aic3104 1v8 pin . 

[Kazi Afroza Sultana]

Hello,

Backfeeding occurs when the voltage at the PMIC’s output (VOUTB) is driven higher than the PMIC’s own output voltage, typically by an external source or large capacitor. nPM1100’s buck cannot sink that much current and has internal MOSFET/body-diode paths that will conduct those reverse currents into internal nodes, potentially overstressing gate drivers, clamp diodes or internal FETs — and causing permanent damage.

Can you tell a bit detail how you have connected the external codec to the audio DK?