TPS25982: Body diode current rating

Steve Widener

Part Number: TPS25982
Other Parts Discussed in Thread: CSD17575Q3

What are the ratings (especially the peak current) for the intrinsic body diode from OUT to IN on this device?

For instance, if there is a short applied to the input of the TPS25982, any charge on the output capacitors will discharge backwards through the part - possibly with a high peak current. Please advise the maximum current ratings for the body diode of the pass mosfet.

over 5 years ago

0 Praveen GD over 5 years ago

TI__Guru 57737 points

Hi Steve,

We generally do not characterize the body diode of the internal FET as it is not intended to carry current. I need to check with our team internally to see if we have any data available for the body diode.

Let me check and get back to you within a couple of days.

0 Praveen GD over 5 years ago in reply to Praveen GD

TI__Guru 57737 points

Hi Steve,

I don't think there should be a problem in discharging the output capacitors to the input vis the body diode.

There would be a problem if the current flowing the body diode is continuous.

Are you looking at protecting the body diode only in this condition (input short and output cap discharging through body diode) or do you have any other scenario ?

0 Steve Widener over 5 years ago in reply to Praveen GD

TI__Genius 11010 points

Praveen -

The primary concern is discharging the output cap when the input is shorted.

This is for a critical design review so we need numeric guidance please.

0 Praveen GD over 5 years ago in reply to Steve Widener

TI__Guru 57737 points

Hi Steve,

Can you share with us the following details,

Output Capacitance Value
Maximum Output/Input Voltage
Minimum Impedance across input when input is short circuited

0 Steve Widener over 5 years ago in reply to Praveen GD

TI__Genius 11010 points

Output Capacitance Value = 338uF
Maximum Output/Input Voltage = 13.8V
Minimum Impedance across input when input is short circuited = 0

0 Praveen GD over 5 years ago in reply to Steve Widener

TI__Guru 57737 points

Hi Steve,

There should be absolutely no problem for TPS25982 in discharging 338 uF through its body diode.

We have customers successfully using it for few mF's of capacitors.

0 Steve Widener over 5 years ago in reply to Praveen GD

TI__Genius 11010 points

What is the basis for this? Where does the diode fail for instance (what peak current?)

It's good to know that other customers have discharged a few mF but there isn't guidance on what the ESR of those caps where or what the shorting impedance is in those cases so we really can't say what margin is available before something fails.

I did look up a typical NEXFET rated for similar voltages & rdson (CSD17575Q3) - the diode looks like ~ 0.4V + 13mOhms (roughly). If the TPS25982 had a similar internal body diode, the maximum peak current would be (13.8V - 0.4V)/13mOhms = 1000A. That seems like a lot and would likely not be seen due to inductances, cap ESR etc. but can we say that a 1000A pulse would not damage the part?

0 Praveen GD over 5 years ago in reply to Steve Widener

TI__Guru 57737 points

Hi Steve,

I am not sure if the way you have calculated the peak current handling capability of the body diode is correct. Can you please reach out to the FET team regarding this.

The body diode for TPS25982 has not been characterized thoroughly. I will check with the design team regarding this but am not sure if we will get what we require and it may take more time to get back to you as well.

Give me a week's time.I will check with the internal team and get back to you.