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Original question:
Hi,
PMIC of TDA4AL can not output VDD_CPU_AVS in our custom TDA4AL board.
Please give some suggestions.
Thanks.
Regards,
Hello Hui,
1, All buck DC-DC have no output. Only one LDO with about 2V.
What is most likely is that there is a power failure on the input voltage supply, where the LDO is in bypass mode, depending on the part number it is most likely LDO2 (Pin 11).
2, How to check the interrupt registers.
Using I2C, the base address is 0x48, read the register 0x5A to 0x6C, same registers for SPI. You should be able to read the registers if there is 1V8 voltage on pins 2 & 3 (VOUT_LDOVINT & VOUT_LDOVRTC). For more details read section 8.5 Control Interfaces in the data sheet. (link here)
3, VCCA_3V3 is not OK, it should be 3.3V, but now it is about 2V. VCCA_3V3 is from VSYS_3V3 via an NMOS switch, VSYS_3V3 is OK. The G of NMOS is not OK, it is from the OPVGDRV of PMIC-A, it is almost 0V.
This points to a short across the NMOS switch, in the power up process the device tests the NMOS switch by driving- the gate low in order to bring the VCCA down a specific amount approx. 60mV. This is the feature described in the datasheet:
The TPS6594-Q1 first checks for possible fail-short condition of the external FET at initial power up. The
diagnostic mechanism pulls the OVPDGRV pin low when VCCA reaches VOVP_FET_Short_TH, and waits until the
voltage on the VCCA pin decreases by VOVP_FET_Short_Hyst before it pulls the OVPGDRV pin high again. This
mechanism effectively disconnects the VCCA pin from VSYS in case of a FET fail-short condition; with the
addition of the diagnostic comparator, however, it also causes a non-monotonic power up behavior with an RC
delay at the VCCA pin. The RC-delay is associated with the input capacitance at the VCCA pin and the internal
pull-down resistor value RVCCA_OVP_PD.
The reason why you may be seeing the LDO on is because of it bypassing the VCCA power which is not correct to the output.
Here's a screenshot of the VSYS vs VCCA:
My suggestion is to verify be taking a scope shot while powering up and if this suggests a FET short, replace the NMOS switch and see if that fixes it.
Best regards,
Nicholas
