TPS3808-EP: Query regarding threshold voltage

Santhosh Kumar S

Part Number: TPS3808-EP
Other Parts Discussed in Thread: TPS3808

Hello Everyone,

I have technical query regarding TPS3808G01-EP. I need to monitor 1.2V supply and we have designed as shown in the attached image.

If I calculate Vit using the formula, I will get Vit=0.4941. For 1.2V, the voltage at the Vsense pin will be 0.983 (due to voltage devider).

So, Reset will be asserted low when 0.983V falls below 0.4941V ? what i have understood is correct or wrong?

over 3 years ago

0 Ben C over 3 years ago

TI__Mastermind 27515 points

Hi Santhosh,

Sorry, but your understanding is not correct. What voltage do you want to see where the /RESET output goes high? The threshold voltage is 0.405V on the SENSE pin. The spec shows that the monitor voltage has to be greater than VIT + VHYS = 0.405V + (0.405V * 1.5%) = 411.1mV (typical) to have /RESET not asserted.

For example, if you use R264=11K and R265=20K, then your voltage to the SENSE pin is 425.8mV @ 1.2V, which is above the VIT + VHYS.

Therefore your threshold voltages will be:

1.159V - /RESET not asserted

1.14V - /RESET is asserted

I hope this answers your question.

Ben

0 Santhosh Kumar S over 3 years ago in reply to Ben C

Intellectual 500 points

Hi Ben,

Thanks for your answer.

I have understood your answer. but i have one doubt.

In my circuit, threshold voltages will be

0.4941 - ./ RESET asserted

0.538 - /RESET not asserted

am i right?

so 1.2V should fall to 0.494 to get /RESET asserted?

so i have to increase the value 0.494 near to 1.2V (i.e 1.14 or near to that ) . are all my understandings are correct?

0 Santhosh Kumar S over 3 years ago in reply to Ben C

Intellectual 500 points

Hi Ben,

I have one more doubt. In this part TPS3808G33MDBVREP, Threshold voltage is fixed to 3.3V right?

So, when will the RESET asserted?

will this be asserted on 3.3V or 3V ?

0 Ben C over 3 years ago in reply to Santhosh Kumar S

TI__Mastermind 27515 points

Hi Santhosh,

The threshold voltage is 0.405V. From the 1.2V rail, what are the voltages you aiming to have the /RESET pin become not asserted and asserted? The equation in the datasheet shows:

VIT' = [1 + (R1/R2)] * 0.405V

where VIT' is the monitored voltage threshold of the rail.

Can you clarify if those voltages below are the rail voltages you want the /RESET output to assert and not assert?

0.4941 - ./ RESET asserted

0.538 - /RESET not asserted

Ben

0 Ben C over 3 years ago in reply to Santhosh Kumar S

TI__Mastermind 27515 points

Hi Santhosh,

See table below:

The table was found in the TPS3808 datasheet

www.ti.com/.../tps3808.pdf

Ben

0 Santhosh Kumar S over 3 years ago in reply to Ben C

Intellectual 500 points

Hi Ben,

0.4941 - ./ RESET asserted

0.538 - /RESET not asserted

above voltages are at the sense pin.

rail voltage is 1.2V

1.14 - ./ RESET asserted

1.159 - /RESET not asserted

I understood your explanation. thank you.

0 Santhosh Kumar S over 3 years ago in reply to Ben C

Intellectual 500 points

Hello Ben,

I got it!

Thanks for your response.

0 Ben C over 3 years ago in reply to Santhosh Kumar S

TI__Mastermind 27515 points

No problem Santhosh and I am glad to be of help! Good luck to you!

Ben

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TPS3808-EP: Query regarding threshold voltage