BQ25890: Using Bi-directional battery switch as discharged FET

NIr Alon

Part Number: BQ25890
Other Parts Discussed in Thread: BQ24266,

Hello all,

In my recent projects, I used the BQ24266 Li-Ion battery charger. this IC contains a BGATE pin which allows me to control an external FET for a low resistance path for the battery discharged current.

In my next project, I plan to use a different charger (BQ25890) which unfortunately doesn't support the BGATE feature.

I was thinking about adding an external battery switch (Vishay SiP32101) as a discharged FET, and control it by using the BQ25890 REGN pin to control the On/Off states of the switch.

The switch is active low, which means that the switch will be on when I disconnect the 5V charging cable, and off when I connect it back again:

Is this a good way to implement the solution, or does someone think that for some reason it will not work well?

Thank you all :)

Nir

over 4 years ago

0 Ning T over 4 years ago

TI__Mastermind 46551 points

Nir,

We are not familiar with SIP32101. It is highly recommended to evaluate the BQ25890 EVM (www.ti.com/.../bq25890evm-664) before making the real design.

Thanks,

Ning.

0 NIr Alon over 4 years ago in reply to Ning T

Intellectual 490 points

Hi Ning,

I'm not expecting you to know SiP32101 or any other component in the world, I was asking the question in the context of functionality of the solution.

Assume that the SiP32101 works like any other discharge FET, it would be wise to connect the FET control to REGN pin? (In terms of the charger different operating states etc.)

Thanks again,

Nir

0 Joel Hernandez II over 4 years ago in reply to NIr Alon

TI__Mastermind 25800 points

Hey Nir,

I think this should be fine as long as the FET is P-Ch. and the back-gate control is reliable for the situation when charging s disabled.

My bigger question is what your purpose is in having this extra external PFET? Are you planning on having high discharge currents?

Regards,
Joel H

0 NIr Alon over 4 years ago in reply to Joel Hernandez II

Intellectual 490 points

Hi Joal,

The main reasons are:

1. High discharge currents

2. Adding additional filtering on the SYS line that will increase the impedance, so while the charger is off, I was planning to bypass the discharge route through the IC.

Thanks for your replay,

Nir

0 Joel Hernandez II over 4 years ago in reply to NIr Alon

TI__Mastermind 25800 points

Hey Nir,

Understood. The only caveat here is that you will need to manually disable the internal Q4 BATFET in order to prevent a flow of current through the part. There is a register bit to do this when in battery only mode. Also, I would consider the behavior during the transition period. If you have no control over the load during discharge + charging disabled, the full load current could still flow through the internal BATFET until the PFET turns fully off AND you turn off the internal BATFET.

Regards,
Joel H

0 NIr Alon over 4 years ago in reply to Joel Hernandez II

Intellectual 490 points

Hi Joel,
Thanks for the insights, I will definitely check the behavior of this setup using EVB's

Best regards,
Nir

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BQ25890: Using Bi-directional battery switch as discharged FET