LM74700-Q1: output or-ing enabling reverse current

Gabriele Rizzi

Part Number: LM74700-Q1
Other Parts Discussed in Thread: BQ25895

Hi, I would like to use 2x LM74700 to protect 2x 18650 LiPo batteries against reverse polarity. The batteries are removable and there is a chance of wrong insertion in the battery holder.

The outputs of the LM74700 are or-wired as I need the capacity of both batteries in parallel.

If one or both batteries are inserted backwards then I would expect one or both LM74700 to be switched off. Is output or-ing causing any potential problems if one of the batteries is inserted backwards while the other is in the correct position?

Since the batteries are rechargeable, I need to accept reverse current, but the reverse current should be "enabled" only if a battery is connected with the proper polarity, and hence the related MOSET is on. Would this work as expected?

Best regards,

Gabriele

over 4 years ago

0 Karikalan Selvaraj over 4 years ago

TI__Genius 16305 points

Hello Gabriele,

Yes, you can use LM74700-Q1 to protect reverse polarity connection to prevent damage when any one of the two batteries are reverse connected.

For this please refer to the datasheet application section 10.2 on ORing Application.

However, if you would like allow reverse current when needed during charging batteries, we need to have additional discrete circuits to enable this work for you.

Let me get back with the circuit to allow reverse current when needed, I will get back tomorrow.

Regards,
Kari.

0 Gabriele Rizzi over 4 years ago in reply to Karikalan Selvaraj

Prodigy 100 points

Hi Kari,

thanks for confirming that the LM74700-Q1 can be used to protect against battery reverse connection.

Indeed I do need also a solution to enable reverse current, as the LiPo batteries need to be recharged! Looking forward to reading from you on this solution.

Best regards, Gabriele

0 Karikalan Selvaraj over 4 years ago in reply to Karikalan Selvaraj

TI__Genius 16305 points

Hi Gabriele,

I would like to let you know that we are working on priority to answer your question, give us more time to get back the circuit fix to allow reverse current.

Regards,
Kari.

0 Gabriele Rizzi over 4 years ago in reply to Karikalan Selvaraj

Prodigy 100 points

Hi Kari,

I appreciate your efforts!

If it can be of any help, the battery charger I am using to charge the batteries is built around a BQ25895.

Looking forward to reading from you soon.

Best regards, Gabriele

0 Karikalan Selvaraj over 4 years ago in reply to Gabriele Rizzi

TI__Genius 16305 points

I am working on getting back to you with an answer, please hold on till tomorrow.

Regards,

Kari.

0 Gabriele Rizzi over 4 years ago in reply to Karikalan Selvaraj

Prodigy 100 points

Hi Kari, any news?
When are you reasonably expecting to be able to get back to me? by the end of this week?
I will need to take a final decision on the circuitry and move forward.

Regards,

Gabriele

0 Karikalan Selvaraj over 4 years ago in reply to Gabriele Rizzi

TI__Genius 16305 points

Hi Gabriele,

Connect a 100 ohm resistor between cathode of IC and drain of the power MOSFET (Q1).

Next between cathode of IC and GND add a 1Kohm resistor and a signal MOSFET(Q2) to disconnect when reverse current blocking is required.

When the MOSFET is turned ON, it should connect a 1kohm resistor from cathode pin to GND. This will draw current through 100ohm resistor and increase the reverse current threshold, thereby allowing reverse current to flow when the signal MOSFET(Q2) is ON. When Q2 is OFF, circuit functions normal and can block reverse current.

Regards,

Kari.

0 Gabriele Rizzi over 4 years ago in reply to Karikalan Selvaraj

Prodigy 100 points

Hi Kari, thanks a lot !
This looks like a simple, clean solution! I will get a couple of demo boards and check how it works.

Thanks again,

Gabriele

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LM74700-Q1: output or-ing enabling reverse current