BQ76952: Ground bias cause to fixed current measurement bias

Francis Jiang

Part Number: BQ76952

Hi Team,

Customer found a ground bias will cause a fixed current measurement bias:

When there is a 10 ohm resistor between BAT- and AFE VSS, the SRP pin will have a 6.8mV voltage to BAT-, and the current measurement shows a false 4A current.

What is the possible reason? Could you please give your professional advice? Thanks.

BRs,

Francis

over 2 years ago

0 Luis H. S. over 2 years ago

TI__Mastermind 42060 points

Hello Francis,

They should not have a 10-Ohm between Vss and BAT-/SRP. BAT- should be referenced to Vss through a 0-Ohm net-tie.

If they replace the 10-Ohm for a 0-Ohm, is the issue still there?

Best Regards,

Luis Hernandez Salomon

0 Francis Jiang over 2 years ago in reply to Luis H. S.

TI__Expert 3160 points

Hi Luis,

With 0ohm resistor, the issue disappeared.

Customer concerns that always there is a ground bias because of parasitic resistance or line impedance, so what is the design note to avoid this issue or whether this issue will lead to other potential problems. Thanks.

BRs,

Francis

+1 Luis H. S. over 2 years ago in reply to Francis Jiang

TI__Mastermind 42060 points

Hello Francis,

They should ensure that the resistance of Vss to BAT- is as small as possible, they could use a ground plane or make the GND/Vss pour as large as possible.

But yes, you do not want to have much resistance between Vss and BAT- as this could cause issues with measurement accuracy and as they saw, current accuracy.

Best Regards,

Luis Hernandez Salomon

0 Francis Jiang over 2 years ago in reply to Luis H. S.

TI__Expert 3160 points

Hi Luis,

Got it! Very clear. Thank you!

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BQ76952: Ground bias cause to fixed current measurement bias