TPS3808-Q1: abnormal output on n_RESET pin

Chuqiang Wen

Part Number: TPS3808-Q1

Hi Expert,

We found a wired phenomenon on TPS3808-Q1, need your support to check the potential reason.

Below is screenshot for TPS3808-Q1 schematic. When SENSE=730mV, we can see n_RESET=1.2V if we add a 27k pull down resistor on it and we remove the R1994 to disconnect with other circuit.

n_RESET pin is open drain output, why it will have 1.2V even we add a pull down resistor on it?

Thanks!

Ethan Wen

over 1 year ago

0 Sila Atalar over 1 year ago

TI__Genius 9820 points

Hi Ethan,

Thank you for your question!

TPS3808G01QDBVRQ1 is an adjustable variant with 0.405V threshold voltage. When Sense pin = 0.73V, it's expected the reset is not pulling low. But can you please first answer below questions so I can better assist you on this and check your schematic for you?

- What is your monitor voltage (Vmon) and resistor divider values?

- What is your pull up voltage and pull up resistor values?

Best,

Sila Atalar

0 Chuqiang Wen over 1 year ago in reply to Sila Atalar

TI__Expert 5845 points

Hi Sila,

See below the feedbacks.

Sila Atalar said:
- What is your monitor voltage (Vmon) and resistor divider values?

Vmon=12V,

Sila Atalar said:
- What is your pull up voltage and pull up resistor values?

R1=62K, R2=4.7k.

Update one more phenomenon. When 27Kohm pull down resistor connect to n_RESET pin, SENSE voltage only have 530mV. MR voltage is 2V.

Looking forward to your feedbacks.

Thanks!

Ethan Wen

0 Jesse Villanueva over 1 year ago in reply to Chuqiang Wen

TI__Mastermind 18870 points

Hi Chuqiang,

Are you able to provide a scope shot of the n_RESET output and SENSE input during this phenomenon? Also, are you able to remove the R1993, since MR is internally pull-up to VDD, if MR is floating, MR should equal to VDD. Finally, is your GND relatively 0V?

Jesse

0 Chuqiang Wen over 1 year ago in reply to Jesse Villanueva

TI__Expert 5845 points

Hi Jesse,

Customer feedbacked that they found the root cause. It is due to the mistake on footprint.

Thanks for your help!

Ethan Wen

0 Jesse Villanueva over 1 year ago in reply to Chuqiang Wen

TI__Mastermind 18870 points

Hi Ethan,

Thank you for the response.

Jesse

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TPS3808-Q1: abnormal output on n_RESET pin