TPS2492: Behavior at Over-Current/Short-Circuit

LIN

Part Number: TPS2492

TPS2492 Datasheet, Page 8, says "If ID < ID_ALLOWED, the amplifier turns the gate of M1 full on because there is no overload condition; otherwise GATE is regulated to maintain the ID = ID_ALLOWED relationship."

ID_ALLOWED corresponds to 50mV of (VCC - SENSE) at low VDS, and < 50mV with power limiting trip.

But it seems ID can go much larger than 50mV at short circuit, is it because ID is "rapidly rising" and the regulation can not respond on time?

over 6 years ago

0 Rakesh over 6 years ago

TI__Guru** 105361 points

Hi Aibing Lin,

Correct. The regulation loop takes time (couple of microseconds) to react due to limited bandwidth. So, for a fast rising current in case of short circuit, the ID exceeds 50mV threshold which increases the overdrive of GATE drive amplifier to pull down (turn OFF) the external FET faster for FET protection.

Best Regards,

Rakesh

0 LIN over 6 years ago in reply to Rakesh

Intellectual 410 points

Hi Rakesh,

Thanks. Any quantified characteristic of this "rapidly rising"?

When ID is "rapidly rising" and the regulation can not respond on time, will fault timer still be triggered once (VCC - SENSE) > 50 mV?

0 Rakesh over 6 years ago in reply to LIN

TI__Guru** 105361 points

Hi Aibing Lin,

I think, the TPS2492 datasheet does not have enough waveform to explain. Can you please refer Figure 23 and Figure 24 in http://www.ti.com/lit/ds/symlink/tps2490.pdf The timer starts when the device enters into current limit mode. For "ripidly rising" current in case of short circuit, the device goes into short circuit mode without triggering the timer.

We don't have quantified characteristic of the "rapidly rising"

Best Regards,

Rakesh

0 Rakesh over 6 years ago in reply to Rakesh

TI__Guru** 105361 points

Hi Aibing Lin,

Does that helped ? Please let me know if you have any open questions?

Best Regards,

Rakesh

0 LIN over 6 years ago in reply to Rakesh

Intellectual 410 points

Hi Rakesh,

Thanks.

Understand the datasheet requires PROG >= 0.4V for power limit setting. If the power limit with PROG = 0.4V is still too high, any recommendation?

0 Rakesh over 6 years ago in reply to LIN

TI__Guru** 105361 points

Hi Aibing Lin,

What is the power limit (W) you are getting with PROG = 0.4V ?

Can you share filled up design sheet http://www.ti.com/product/TPS2492/toolssoftware

Best Regards,

Rakesh

0 LIN over 6 years ago in reply to Rakesh

Intellectual 410 points

Hi Rakesh,

I have high current limit at 130A. When PROG = 0.4V, the power limit is about 530W, this is way too high.

Understand when PROG < 0.4V, the power limit is not accurate, but it will be lower anyway, right?

Any info on power limit setting when PROG < 0.4V?

Thanks.

0 Rakesh over 6 years ago in reply to LIN

TI__Guru** 105361 points

Hi Aibing Lin,

Yes, it should be lower.

We have characterized PROG between 0.4V to 4V

Best Regards,

Rakesh

0 LIN over 6 years ago in reply to Rakesh

Intellectual 410 points

Hi Rakesh,

From previous discussion, if ID is "rapidly rising" and exceeds ID_ALLOWED, the fault timer is not triggered.

Just wondering, if this "rapidly rising" current exceeds ID_ALLOWED but is not high engouh to be recognized as short-circuit, will TPS2492 turn off the MOSFET? How fast?

Thanks.

0 Rakesh over 6 years ago in reply to LIN

TI__Guru** 105361 points

Hi Aibing Lin,

In that situation, the device treats as overload and provides regulated current (as per set current limit) till the fault timer expires. After that the device turns off the MOSFET with a max propagation delay (tD_FAULT) of 1 us.

Best Regards,

Rakesh

0 LIN over 6 years ago in reply to Rakesh

Intellectual 410 points

Hi Rakesh,

Thanks.

So if ID is "rapidly rising" and exceeds ID_ALLOWED, the fault timer will be triggered, right?

0 Rakesh over 6 years ago in reply to LIN

TI__Guru** 105361 points

Hi Aibing Lin,

yes, if ID value not enough to create large overdrive to treat device as short circuit then it is treated as overload to trigger the fault timer.

Best Regards

Rakesh

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TPS2492: Behavior at Over-Current/Short-Circuit