BQ4050: SMBC rise time is 1.4us longer than timing requirement in datasheet

Howard Zou

Part Number: BQ4050

Hi, my customer test BQ4050 on board with pull SMBC to external 3.3V with R5 and R6 shown below.

The waveform of SMBC below shows that the rise time is 1.4us, is it acceptable? If not, could we decrease R5, R6 value? We choose 200ohm and 100ohm according to the typical application circuit in the datasheet.

over 5 years ago

0 Onyx Ahiakwo over 5 years ago

TI__Guru* 76230 points

Hi Howard

Pls ensure that the rise time meets the smbus spec. The smbus spec can be downloaded online

thanks
Onyx

0 Howard Zou over 5 years ago in reply to Onyx Ahiakwo

TI__Genius 12365 points

Hi,

it exceeds the requirement in the datasheet 6.33 Timing Requirements: SMBus

I think we should decrease the pull up resistor value, but I'm not sure if it's okay to decrease the value to 1/2. Since 200ohm and 100ohm is suggested in the typical application in the datasheet. Why we suggest 200ohm and 100ohm?

0 Howard Zou over 5 years ago in reply to Onyx Ahiakwo

TI__Genius 12365 points

Onyx,
is it possible that we go with 1.4us rise time? Since the clock frequency is just 27k in the real application.
Right now the 1.4us doesn't cause communication error.
I can find the SMBUS spec requiring <1us rise time. But nobody knows why and what if it's violated.

0 Batt over 5 years ago in reply to Howard Zou

TI__Mastermind 42535 points

I think you can reduce the pullup resistors to 100 Ohm. That may fix this.

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BQ4050: SMBC rise time is 1.4us longer than timing requirement in datasheet