Contents
Is the VBAT pin on a stm32f091 working?
I’m trying to set-up a STM32F091 with a battery connected straight into the VBAT pin. For the first couple times I turned on this vbat at 3V, it worked ok (no weird behavior). However, after trying to program the MCU via SWD, this VBat pin became a low impedance path to ground (around 150 Ohms) sinking 20mA.
How is the VBAT pin connected to the battery?
The circuit is a straight connection between the battery and this pin. All others power pins are connected according to the datasheet. An interesting fact is that the ADC channel 18 (ADC_IN18) measures the voltage on VBat pin correctly. Have anyone experienced this before? Am I missing something when using Vbat or is this a configuration issue?
How many ohms does a VBAT pin sink?
However, after trying to program the MCU via SWD, this VBat pin became a low impedance path to ground (around 150 Ohms) sinking 20mA. At first I thought this low impedance path was in my board, but then I removed the MCU and measured the resistance on the chip between pins VBAT and Ground, getting 159 ohms as a result.
Why is the VBAT pin sinking a lot of Ma?
The localised issue around the VBAT pin (it seems to be localised since, as you said, other parts of the MCU work OK) suggests that VBAT is involved somehow. You mentioned VBAT being supplied from a battery, and later you said it is being supplied from a bench power supply (PSU).
How can I measure the VBAT voltage throuth ADC of STM32F103?
And it turns out to be really low, a maximum of 50nA over the whole temperature range. In the end we are looking at 150nA maximum, 12nA typical at 25°C additional drain from the battery with this analog switch. It provides a nice low impedance path to measure the voltage for the ADC.
What’s the maximum voltage of the VBAT pin?
However, the maximum voltage on the discharging curve of this battery is 4.2v which is above the maximum operating voltage of the Vbat pin (3.6v). My question is can I directly connect the battery to the Vbat pin, or should I use the voltage divider to divide the battery voltage into a suitable range?
How long does a CR2032 VBAT battery last?
If this pin is not tied to Vss you will drain the battery in a week. Check the datasheet for more. When PDR_ON pin is connected to VSS (Internal Reset OFF), the VBAT functionality is no more available and VBAT pin should be connected to VDD. A CR2032 battery will last for more than 10 years.
Is the PDR _ on pin tied to VSS?
With lower pin count devices (64, 100) this pin is tied to Vss internally, but on higher pin count devices (144, 176) you have to connect it to a positive or negative potential. If this pin is not tied to Vss you will drain the battery in a week. Check the datasheet for more. Edit: PDR_ON should be tied to Vdd, not Vss.
What does R26 do in a VBAT circuit?
R26 can simply be there for debugging purposes or to add extra supply decoupling (if needed) for the Vbat pin. Then R26 could be 100 ohms for example and that would provide increased supply filtering for Vbat. Those 100nF are probably decoupling capacitors.