Issue with V_BAT Connection on Custom STM32F407VGT6 Board

[rohithinthingstech]

Hello everyone,

I have designed a custom board using the STM32F407VGT6, and I have connected a 3V coin cell battery (CR2032) to the V_BAT pin as shown in the schematic below:

V_BAT Circuit Details:

• A 3V battery is directly connected to the V_BAT pin.
• A 0.1µF capacitor (C14) is placed across V_BAT and GND.
• V_BAT is connected directly to the STM32.

However, I am facing an issue where I do not measure any voltage at the V_BAT pin on my board. It seems like the battery is not supplying power to the backup domain.

1. Why am I not getting voltage on the V_BAT pin?
2. Are there any hardware design issues with my schematic?
3. Is there any special configuration required in firmware to enable the backup domain power?

I have attached my schematic for reference.

[mƎALLEm]

Hello,

You can refer to the STM32F4G EVAL schematics:

As you can see nothing special:

For the code you can refer to the RTC calendar example here.

[TDK · Accepted solution]

> do not measure any voltage at the V_BAT pin on my board

A multimeter across the battery should show voltage. If using the ADC, show relevant code. Should be getting something. Nothing wrong with the schematic snippet.

[Andrew Neil]

You can paste the image directly into the post - where we can see it:

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@rohithinthingstech wrote:

I do not measure any voltage at the V_BAT pin on my board. It seems like the battery is not supplying power to the backup domain.

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Is the battery dead?

Have you measured to see if current is being drawn from the battery?

@rohithinthingstech wrote:

I have designed a custom board .

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Have you checked the layout for shorts?

Have you checked the assembly for shorts and bad joints?