BQ40Z50: Bq40z50-XX SMB SPEC information compare with SBS 1.1 SPEC

Lucas Chao1

Part Number: BQ40Z50
Other Parts Discussed in Thread: BQSTUDIO,

Hi, This Question is base on bq40z50-xx series.

my customer use EV2300 and bqstudio tool to simulate a host communication with gauge, they found the SPEC information about Timing Requirements: SMBus Clock rise time and Clock fall time calculation is different with SBS 1.1 SPEC, those 2 pictures are same waveform but different with two SPEC effective unit, I tested the EV2300 pull High is around ~3.14V, if use this value to calculate that tR and tF, the TI SPEC value will over that define a lot,

may I studying from you how to calculate this problem and clarify this question, Thanks !

TI SPEC information

over 5 years ago

0 Lucas Chao1 over 5 years ago

TI__Prodigy 60 points

0 Lucas Chao1 over 5 years ago

TI__Prodigy 60 points

0 Lucas Chao1 over 5 years ago in reply to Lucas Chao1

TI__Prodigy 60 points

0 Kang Kang over 5 years ago in reply to Lucas Chao1

TI__Mastermind 24870 points

Hello Lucas,

In this case, my suggestion is to follow the TI datasheet.

The rise and fall times defined here are with respect to the pull up voltage.

The smbus spec has a high and low time that the gauge needs to abide by. These are Bus Hi and Bus Lo times.

Thanks

0 Lucas Chao1 over 5 years ago in reply to Kang Kang

TI__Prodigy 60 points

Hi Kang:

The problem is they question that calculate values exceeds the specifications defined by bq40z50 TRM.

TRM define that tR and tF value is same with the SBS1.1, but if use that formula in TRM(tR-Clock rise time 10% to 90% = 1000ns & tF-Clock fall time 90% to 10% = 300ns)

They want to know how to use the 3.14v EV2300 pull high value to calculate it and meet the TRM condition tR = 1000ns, tF = 300ns. .

Use this voltage value to calculate, that will over TRM define nearly double.

if this pull high value 3.14v is a wrong choose, please teach and explain how to calculate it.

Thanks !

0 Kang Kang over 5 years ago in reply to Lucas Chao1

TI__Mastermind 24870 points

Hello Lucas,

Yes, these tR and tF times are soft specs. What I meant to say earlier is as long as they do not violate the bus hi and bus lo times, the communications should be okay.

To meet these conditions, they will need to use a stronger pull-up. It is an RC time constant here. They should try to reduce bus capacitance if possible as well.

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BQ40Z50: Bq40z50-XX SMB SPEC information compare with SBS 1.1 SPEC