LM74502H-Q1: Schematic Review

Hi Ibrahim,

Please find my response inline below

1) Is this device suitable for automotive oil/water pump application?
150W motor, 12V Battery, 13A rated with 40-50A peaks.
Must be protected against to the typical surges on automotive power rail (in picture).

A1) Yes, LM74502-Q1 in surge stopper topology can be used to protect from all automotive transients shown in the image.

2) Is there available Grade0 alternative of this IC or will it be available in future?

A2) Only grade Q1 is available and we do not have any plans for Q0 variant of this device in the future.  

3) Without the TVS diode, like in the schematic,
What could be the expected behavior with ISO7637 pulse 1 transient?
Is it possible to simulate this device with that ISO pulse and see the voltage stresses at each node?

A3) Without TVS diode, When ISO Pulse-1 the voltage at the input of LM74502-Q1 can swing negative below the 65V which is beyond the Abs Max rating of the IC which can damage the device. Yes, you can simulate the device using LM74502 PSpice Transient Model

4) If the TVS is mandatory for -150V pulse (expected the positive pulse protected up to 100V),
is it possible to use only a unidirectional TVS to protect negative only?

A4) Yes, you can use unidirectional TVS diode only to protect for negative transients. You need to connect a diode in the series (but in reverse polarity) with the TVS to protect the TVS from conducting when positive voltage is applied. 

5) In the overvoltage clamp mode, switching of the mosfet should require any EMC concerns?
If yes is there any recommendation for suppression of the switching noise?

A5) There is no EMC concern during OV clamp operation as this is only a transient condition and not a DC condition.

6) Is there any issue with the 40V Q2 FET usage when the overvoltage limited at 28V like in the schematic?
What could be the formula between the min Q2 FET voltage and Overvoltage limitation?

A6) For positive voltages applied at input, the body diode of Q2 would be forward biased and conduct even when the FET is OFF. Hence, there will be no issue with the VDS rating of the FET during positive input voltages.

7) For the FETs, RDSon must be selected as low as possible but is there any limit or consideration for the gate charge?

A7) Higher the gate charge, higher the turn ON and turn OFF time considering the fixed sink and source current capability of the controller. Also, the minimum charge pump capacitor required would increase for FETs with higher gate capacitance as per the equation below. 

8) Is there any comment on the 50V capacitor usage?

A8) Input capacitors need to be rated for more than the max transient voltage that can occur at the input. So, you will have to increase the input capacitors rating for >= 100V. The output side is protected from over voltages, hence a 50V rated capacitor should be okay.

Thanks for your comments,

Regards