BD71847 can't power IMX8MM

[484999697]

Hi,

    My design reference IMX8MM-EVK design.

    Only  “LDO1” and “LDO2” has output,and the “PMIC_ON_REQ” pin can only provide 0.6V level for BD71847,should I give an external pull-up for BD71847? 

[_Steph_]

Hi !

Just wonder if you find a solution to your problem ? 
I have a custom board with same reference design and first prototype has same behaviour than yours => PMIC_ON_REQ is only 0.6V and so PMIC cannot start, as he requieres 1.44V minimum to start. 

Wanted to try some pull ups on PMIC_ON_REQ to see if it changes anything.

thanks for any reply.

[weidong_sun]

Hi Peter,

There exists internal pull-up resistor on the pin PMIC_ON_REQ, See datasheet and schematic, please!

1. in datasheet

2. in schematic

So you don't need external pull-up resistor on the PIN.

BUT as a test, you can try to pull it up outside, checking if BD718847 can normally work.

3. About the issue you encountered

You can check if these several pins' level are normal.

Try it , please!

Have a nice day!

B.R,

Weidong

[484999697]

Hi Weidong,

Thank you very much for your reply. 

Only pin "WDOG_B" is not low level,and extra pull-ups on pin "PMIC_ON_REQ' are useless.

But I found there is no program on Soc,this may cause the system to only work in SNVS mode,is this the cause of insufficient drive level?

Do I need to write an additional program to the register to drive the "BD71847"?

Have a nice day!

Peter

[imx8student]

Hi Peter,

Did you find the explaination of this behavior ? Did you put your pull-ups for PMIC_ON_REQ on 1V8 SNVS power ?

Best Regards,

[weidong_sun]

Hi Peter,

   PWRON pin must be HIGH, and PMIC_ON_REQ should also be HIGH. otherwise PMIC can't normally work.

in SNVS mode, CPU can't run any application, so you couldn't configure PMIC via I2C.

   You should try your best to find why PWRON and PMIC_ON_REQ are both LOW.

Have a nice day!

B.R,

Weidong