BQ25504 external load switch

Antonis Spiliopoulos

Other Parts Discussed in Thread: BQ25504

Hello,

I am using the reference design of the BQ25504 to charge a battery from a solar cell and am able to power the load when it is connected directly to the VSTOR pin.

The problem is that when I attach an external load switch (BAT_OK drives an NMOS which drives an PMOS) to protect the battery from deep discharging, as proposed in the datasheet, I get no voltage at the output.

Any suggestions on the circuit or the type of the FETs I have to use?

over 10 years ago

0 Jeff F over 10 years ago

TI__Guru**** 165766 points

Is your circuit like the one below? Is VBAT_OK working as expected?

0 Antonis Spiliopoulos over 10 years ago in reply to Jeff F

Prodigy 30 points

Yes my circuit is like this one.

By VAT_OK threshold do you mean the voltage at the BAT_OK pin (3.1V for the reference design)? If so I think this is the problem.

0 Jeff F over 10 years ago in reply to Antonis Spiliopoulos

TI__Guru**** 165766 points

The VBAT_OK signal output = VSTOR voltage, which should also be VBAT voltage. The VBAT_OK signal goes high when VSTOR rises above the VBAT_OK_HYST threhsold and goes low when VSTOR falls below VBAT_OK threshold, where both thresholds are set by external resistors. Also, your VBAT_UV threshold should between 1.9V and the lower VBAT_OK threshold.

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BQ25504 external load switch