TPS7B7702-Q1: Co-work with MCU ADC

Albert Sun

Part Number: TPS7B7702-Q1
Other Parts Discussed in Thread: OPA397, TLV906X, OPA392, OPA376-Q1, OPA388-Q1

Hi Team,

MCU ADC has leakage current about 1uA. When it is sensing voltage at SENSEX pins, it can deteriorate the current sense accuracy. What is the workaround for this problem?

-A

over 2 years ago

Nick Butts over 2 years ago

TI__Mastermind 47615 points

Hi Albert,

What current level are you expecting to be monitoring? The minimum specified valid SENSEX current is 5mA / 198 ≈ 25uA, so a 1uA leakage introduces about 4% error in addition to the 20% accuracy spec. If the current level is much higher, the 1uA leakage contributes little to the overall SENSEX accuracy spec.

I'm not aware of a hardware workaround for this. The current coming out of SENSEX is set for a given load current and if there's nothing that can be done for the ADC leakage, then there's not a lot that can be done about it.

Regards,

Nick

Albert Sun over 2 years ago in reply to Nick Butts

Intellectual 350 points

Hi Nick,

Yes I was thinking about 5mA accuracy. How about adding a follower amplifier between ADC and 7B7702? What is the recomendation for this amplifier?

-A

John Schneider over 2 years ago in reply to Albert Sun

TI__Genius 12511 points

Hi Albert,

Sorry for the delay in response, Nick will get back to you tomorrow when he returns from the holiday.

Nick Butts over 2 years ago in reply to Albert Sun

TI__Mastermind 47615 points

Hi Albert,

Yes that should work. I will refer you to the amplifiers group to help with your question of which device is a good fit.

Regards,

Nick

Michael Hartshorne over 2 years ago in reply to Nick Butts

TI__Genius 12685 points

Hi Albert,

The OPA397 is a good device to buffer this node - it has fast settling that will be suitable for medium-resolution ADC's (no problem for most 14-16 bit, depending on the acquisition time). Also, offset and bias currents are very low so accuracy is maintained.

For a lower cost device, the TLV906X amplifiers are a good alternative.

Let us know if there are any more questions here.

Best Regards,
Mike

Albert Sun over 2 years ago in reply to Michael Hartshorne

Intellectual 350 points

Hi Mike,

Do you have automotive version?

-A

Michael Hartshorne over 2 years ago in reply to Albert Sun

TI__Genius 12685 points

Hi Albert,

Ah yes of course- the OPA397 is not yet auto-qualed., but the higher-performance version will be next year called OPA392.

The best device at the moment then is probably OPA376-Q1, or OPA388-Q1 for ultra-low offset chopper amp.

Regards,
Mike

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TPS7B7702-Q1: Co-work with MCU ADC