AM3352: GPIO state when device is unpowered

TS Yang

Part Number: AM3352

Hi,

I have configured GPIPO_20 (COLD_RST) as cold reset (PMIC power off) as below.
It is low on the AM335 even though it is pulled up to high the initial value.
The power supply of the AM3352 is only + 1.8V_RTC.
I wonder why AM3352 hold it as low.

thanks,

over 6 years ago

0 Biser Gatchev-XID over 6 years ago

TI__Guru**** 393215 points

GPIO states are undefined when the processor is unpowered. You will need an external circuit to keep your COLD_RST signal high when PMIC is powered off.

0 TS Yang over 6 years ago in reply to Biser Gatchev-XID

Genius 4800 points

As you can see in the schematic,
COLD_RST is pulled up to external power source, not PMIC power.
And the AM3352 has only + 1.8V_RTC connected, but the external power source is connected to the PMIC.
We have received inquiries from above.

0 Biser Gatchev-XID over 6 years ago in reply to TS Yang

TI__Guru**** 393215 points

This is even worse. No voltage should be applied to processor I/O pins while the device is unpowered.

0 TS Yang over 6 years ago in reply to Biser Gatchev-XID

Genius 4800 points

Last time you told me to connect external power as below,
Not this time. That's the opposite.

"GPIO states are undefined when the processor is unpowered. You will need an external circuit to keep your COLD_RST signal high when PMIC is powered off."

0 Biser Gatchev-XID over 6 years ago in reply to TS Yang

TI__Guru**** 393215 points

By external circuit I didn't mean a pullup resistor (R246 from what I can see on the image), but some active circuit that will effectively prevent the external voltage from reaching the processor GPIO pin when the processor is unpowered.

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AM3352: GPIO state when device is unpowered