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Pull up resistor in STM32WBA5MMG RESET circuit

Hariom
Associate III

Dear Team,

I have a board contain STM32WBA5MMG and  AD5941. We have provided a single RESET for both the chips.

The circuit is given below.

Hariom_0-1776960825992.png

May Iknow will this cause any issues.

 

Regards

Hiyo

1 ACCEPTED SOLUTION

Accepted Solutions
Peter BENSCH
ST Employee

No STM32 requires a pull-up resistor at the reset pin (in your case R36 = DNP), because there is already an internal pull-up present (see RM0493, 12.3.2).

The reset pin also acts as an output if an internal reset is triggered in the STM32, so any devices externally connected to NRST also receive this reset signal. According to the data sheet, the AD5941 needs at least 1µs to detect a reset; the internal pulse generator in the STM32 typically produces a pulse that is at least 20µs long (unfortunately, the specification for tO(NRST) is mentioned in RM0493 but still missing from the data sheet of the STM32WBA55UG, however, the pulse generator should be identical to that of other STM32 devices).

Summary: In my humble opinion, there should be no problem connecting /RESET and NRST.

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

View solution in original post

2 REPLIES 2
Peter BENSCH
ST Employee

No STM32 requires a pull-up resistor at the reset pin (in your case R36 = DNP), because there is already an internal pull-up present (see RM0493, 12.3.2).

The reset pin also acts as an output if an internal reset is triggered in the STM32, so any devices externally connected to NRST also receive this reset signal. According to the data sheet, the AD5941 needs at least 1µs to detect a reset; the internal pulse generator in the STM32 typically produces a pulse that is at least 20µs long (unfortunately, the specification for tO(NRST) is mentioned in RM0493 but still missing from the data sheet of the STM32WBA55UG, however, the pulse generator should be identical to that of other STM32 devices).

Summary: In my humble opinion, there should be no problem connecting /RESET and NRST.

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Hi Peter,

Thank you very much.