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BQ2060A: How to choose SMBC SMBD resistor value on BQ2060A ?

Jerry Lin6
Prodigy 30 points
Part Number: BQ2060A
Other Parts Discussed in Thread: BQ2060

Dear Sir,

my customer's BQ2060A board is communicating with CPU board through SMBC SMBD.

BQ42060A board is as below: R4, R5, (for SMBC) ,  R6, R14 (for SMBD) is NOT the same as recommended in BQ2060A datasheet.

( Note : my customer's BQ2060A  board designed for mass production over 15 years.)

1. We encountered sometimes can not detect BQ2060A board when customer current designed as above circuit 

   meanwhile we have measured waveform of SMBus just found SMBC falling occurs bigger ringing as below :

 

2. We have modified R4, R5, (for SMBC)  from 10 ohm change to 100 ohm like as BQ2060A datasheet then test over 100000 times still can detect BQ2060A  normally 

    meanwhile we have measured waveform of SMBus just found SMBC falling occurs smaller ringing as below :


 

Due to we have all check SMbus waveform for High , Low , Setup , Hold time all can meet BQ2060A spec.

So we wonder to know how to calculate the right resistor value in the circuit ? 

Why BQ2060A 's SMBC used 10 ohm will happened stronger reflection NOISE ? 

Please advise,

Regards,

Jerry

 

  • 0
    TI__Guru** 105770 points

    Hello Jerry,

    The EVM users guide shows an example of the circuit using 100ohm resistors in series with the line: https://www.ti.com/lit/ug/sluu179/sluu179.pdf?ts=1597855109354&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ2060A

    Is this a new layout with this chip? Or this error is occurring after 15 years of production with same resistors and layout? Can you share the layout?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hi Wyatt,

     Thanks for your replied, Actually we have informed my customer to understand BQ2060A's circuit using 100 ohm from EVM user guide , but this battery board NOT new layout design with BQ2060A.

    My customer mentioned this production using the same resistors & layout over 15 years NOT new layout design , We can't get layout file from customer site.

    In fact , We really wnat to know how to calculate for damping resistor value on SMBC & SMBD ?

    ( We're confused why using 10 ohm for both on SMBC & SMBD from my customer design , The BQ2060 of EVM designd using 10 ohm before 15 years ? )

    Please advise..Tks!

    Jerry

  • 0 in reply to Jerry Lin6
    TI__Guru** 105770 points

    Hello Jerry,

    So this error is occurring on a board and chip that hasn't changed for 15 years, now with a new lot of the bq2060a they are running into this communication problem? If so we will have to check if the hardware or firmware has been modified at all.

    I don't believe TI has documentation on selecting a dampening resistor, usually using 100ohm is the standard.

    The design must've been updated from the old EVM to the 100ohm value, it's possible because of an issue like this.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hi Wyatt,

       Thanks for your prompt reply on this issue, we will inform cutomer to using 100 ohm on damping resistor from TI suggestion.

    Regards,

    Jerry