TPS25924: countermeasure for reverse voltage condition

Hi Sasaki,

• During normal operation: There is current flow from Vin to Vout. Due to the Rdson of the internal FET, there is voltage drop across the FET and Vout is always less than Vin.
• During reverse Voltage Conditions: The body diode of internal FET is Forward biased and there is no Protection for Reverse Current. This is because in TPS25924x there is no Blocking FET which is connected back to back to block the Reverse Current. TPS2594x series of devices have blocking FET integrated. So, this family of devices support  Reverse Voltage and Reverse Current Protection..
• If there is a condition like Short Circuit or Over Current  which causes the FET to TurnOff, then there is a possibility of negative voltage being developed at Vout due to inductance in the output path. During this condition, we need to make sure that the Vout does not fall below its 'Minimum voltage = -0.3V'. For this condition we place a Schottky Diode at the output so that the energy in the output inductance freewheels through the Schottky and the Vout is clamped to 'GND-Schottky Diode drop'.

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Regards,

Praveen

Praveen-san,

When we use TPS25924x, do you think that schottky diode between VOUT and VIN is valid solution for reverse voltage condition to follow absolute maximum rating?

Best Regards,
Kohei Sasaki

Hi Kohei Sasaki,

If there is a reverse voltage, the internal  body diode of the FET conducts and clamps the Vout to Vin+0.3V.

So, you don't need to place any  external Schottky Diode from Vout to Vin.

Regards,

Praveen

Please click "This resolved my issue" button if this post answers your question.

Praveen-san,

In FET off state, I think body diode of FET clamps the Vout to Vin. However, is it Vin+0.3V? I think body diode VF is about 0.5V to 0.6V.
If it is so, it is over absolute maximum rating.

How about the FET ON state?
About 10A reverse current is needed so that Vout voltage becomes 0.3V higher than Vin voltage.
In this case, I think there is possibility that device is damaged.

Should we take care device protection when noise is added output line and Vout voltage becomes 0.3V higher than Vin?
Isn't it needed because noise don't have so power? Does not the voltage rise up so much?

Best Regards,
Kohei Sasaki

Hi Kohei Sasaki,

Can your system have 300mV of noise on the output ? What is the load at output?
The current through the internal Body Diodes should not be more than 100mV. If there is a possibility of reverse current more than 100mV, place a Schottky Diode across Vout to Vin.
TPS25924 does not protect for reverse current. In case your system requires reverse current blocking, you need to consider TPS2594x which has blocking FET.

Regards,
Praveen

Praveen-san,

Actually 300mV noise is not observed.
We are considering protection solution if such case happens.

I understood that schottky diode may protect reverse voltage condition, but so large reverse current doesn't flow by noise.
Is this right?

Best Regards,
Kohei Sasaki