LM74700-Q1: Question about FET orientation in design

jediengineer

Part Number: LM74700-Q1
Other Parts Discussed in Thread: LM74502-Q1, , TPS25961, TPS2521, TPS25947, LM74800-Q1, TPS2663, LM76202-Q1

Simple question - I'm considering using the LM74700QDBVRQ1 as a NMOS power (DC) switch controller. Can I connect the FET in the reverse direction as shown in the diagram (power flows from source to drain)? I don't want any current leaking across the FET through the body diode. I need to use this as a hard power switch.

Thanks!

over 1 year ago

0 Praveen GD over 1 year ago

TI__Guru 57737 points

Hi,

Please refer to the e2e FAQ below,

Can an Ideal Diode Controller used as load switch with external MOSFET?

https://e2e.ti.com/support/power-management/f/power-management-forum/994549/faq-can-an-ideal-diode-controller-used-as-load-switch-with-external-mosfet

You can consider using LM74502-Q1 for driving a FET in load switch orientation.

0 jediengineer over 1 year ago in reply to Praveen GD

Prodigy 165 points

Thanks Praveen. So if I understand correctly, the LM74700 will NOT operate the FET in load switch orientation?

0 Praveen GD over 1 year ago in reply to jediengineer

TI__Guru 57737 points

Yes, LM74700-Q1 is not suitable to drive the FET in load switch orientation.

Can you share your requirements like Vin range, Load current, application and other features required so that I can suggest a better part ?

0 jediengineer over 1 year ago in reply to Praveen GD

Prodigy 165 points

I actually have two use cases. One at 48V, for which the 74502 will work, and the other at 3.3V. I'm just now realizing that the 74700 has a lower limit of 3.3V - do you have an alternative for switching a load at that low of a voltage?

0 Praveen GD over 1 year ago in reply to jediengineer

TI__Guru 57737 points

Hi,

What is the load current on 3.3V rail ? Do you need a Q1 qualified part ?

0 jediengineer over 1 year ago in reply to Praveen GD

Prodigy 165 points

It's a small load, less than 500mA Q1 qualified would be good, but I'll entertain non Q1 versions.

0 Praveen GD over 1 year ago in reply to jediengineer

TI__Guru 57737 points

Please check if TPS25961 can meet your requirement. This is an FET integrated eFuse with Adjustable Current Limit and Short-Circuit Protection

0 jediengineer over 1 year ago in reply to Praveen GD

Prodigy 165 points

I've looked into this particular part already. It doesn't seem to offer reverse current protection.

0 Praveen GD over 1 year ago in reply to jediengineer

TI__Guru 57737 points

Yes, TPS25961 device does not offer reverse current blocking (RCB) as it only has load switch FET. For RCB functionality, ideal diode FET is required.

For 3.3V rail, you can have a look at TPS2521, TPS25947

Please be aware that LM74502-Q1 can drive both load switch and Ideal diode FET, it can only support input reverse polarity protection but does not offer RCB.

For 48V if RCB is required and load current is lower you can consider using integrated solutions like TPS2663, LM76202-Q1, TPS2660x . For higher load currents, you will need controller + external FET solution like LM74800-Q1.

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LM74700-Q1: Question about FET orientation in design