BQ76952: IC drawing 4mA current from main power pin at idle state

Mrinal Mani

Part Number: BQ76952

Hello

We have designed BMS using 76952 and over the last few months close to 1K BMS have already been installed in the field. Everything seems to work OK but the issue is that the IC draws 3.9mA current from BAT pin (pin no 47). Even when the MCU is not powered ON and there is no communication with the AFE, as soon as the BAT pin is powered up from top most cell it begins to draw close to 4mA. The datasheet however mentions only a few hundred uA. The battery pack is 15S-LFP 48V and the Bat pin is powered from the top most cell through a diode.

The circuit diagram is attached above. Current sensing and MOSFET control is being handled externally. Please suggest what could be the reason for the excessive current draw. 5V is supplied from an external DC-DC controller. Even when the 5V supply is not present, the AFE draws current from BAT pin.

Thank you

over 1 year ago

0 Max Verboncoeur over 1 year ago

TI__Mastermind 25790 points

Hi Mrinal,

I suggest that you check all of the connections to see where this current is coming out from. I would suspect REG1, although it would be good to check everything to see if the device is damaged in some way.

Regards,

Max Verboncoeur

0 Mrinal Mani over 1 year ago in reply to Max Verboncoeur

Prodigy 205 points

Hi Maxwell,

Thanks for the reply. After some testing, when I float the BREG pin, the current bleed stops. The BREG was supposed to drive an external BJT, but since a BJT is not being used, we connected the pin to the external 5V supply coming from a DC-DC converter. When this pin is connected to 5V, approx. 4mA current is drawn from the main 48V line powering the chip. When BREG pin is made to float while rest of the connections are the same, the current reduces to a few uA.

Is there a possible reason why the BREG pin could be drawing current?

Thanks

0 Max Verboncoeur over 1 year ago in reply to Mrinal Mani

TI__Mastermind 25790 points

Hi Mrinal,

This is very interesting. The way you have it connected in the schematic is the correct way to do it:

Could you check what Settings:Configuration:REG0 Config is set to? It should be 0x00 if you do not intend to use the pre-regulator.

Regards,

Max Verboncoeur

0 Mrinal Mani over 1 year ago in reply to Max Verboncoeur

Prodigy 205 points

I will check the settings for REG0 and update today.

0 Max Verboncoeur over 1 year ago in reply to Mrinal Mani

TI__Mastermind 25790 points

Hi Mrinal,

I'll wait to hear back on the results.

Regards,

Max Verboncoeur

0 Mrinal Mani over 1 year ago in reply to Max Verboncoeur

Prodigy 205 points

I have checked the REG0 resistor and it is NOT set to 0. We are simply not using power from the LDOs but have not disabled REG0 in the settings. Do we need to disable REG0?

Thank you

0 Max Verboncoeur over 1 year ago in reply to Mrinal Mani

TI__Mastermind 25790 points

Hi Mrinal,

Yes, if the pre-regulator is not in use, the REG0_EN bit should be 0. I expect the device is trying to drive that pin and pulling a large current due to it being connected to REGIN. Setting the bit to 0 should fix this.

Regards,

Max Verboncoeur

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BQ76952: IC drawing 4mA current from main power pin at idle state