BQ2205LY: RST remains at LO

Hiroaki Yuyama TED

Part Number: BQ2205LY

Dear, support team.

Even if VCC powers up, RST will remain at LO.
The condition is that when the VCC is OFF, the BCP backup battery is 3 V → 0 V → 3 V. After that, power up VCC.
With BCP backup battery voltage fixed at 3 V, RST goes HI when VCC powers up.
The customer pulled out the battery to change the backup battery.
The VCC voltage is 3.2V.

Is there no description on the data sheet and conditions for RST to be LO?

Best Regards,
Hiroaki Yuyama

over 7 years ago

0 Hiroaki Yuyama TED over 7 years ago

Expert 1730 points

Attach the waveform.

Probe CH：

CH1 RST pin16

CH2 VCC3.3V pin12

CH3 V out pin13

CH4 BCP pin9

RST=Constant LO

RST=LO to HI

0 Onyx Ahiakwo over 7 years ago in reply to Hiroaki Yuyama TED

TI__Guru* 76230 points

Page 7 of the data sheet describes conditions for the rst pin to be low.
thanks
Onyx

0 Hiroaki Yuyama TED over 7 years ago in reply to Onyx Ahiakwo

Expert 1730 points

Onys-san.
Thank you for your reply.

I will ask about Power-On Reset on page 7.
"With valid battery voltage on BCP, RST remains valid for VCC = VSS."

When power supply to bq 2205 is BCP, when power is on from VCC, does RST mean LO?
I can't understand "RST remains valid for VCC = VSS."

V PFD (Supply switch over voltage) is 2.95 V Max.
Is VCC valid if VCC is higher than VPFD?
Or if BCP is higher than VCC, is BCP valid?

Best Regards,
Hiroaki Yuyama

0 Hiroaki Yuyama TED over 7 years ago in reply to Hiroaki Yuyama TED

Expert 1730 points

Dear,BQ product support Team.

I will ask a simple question.
Does bq 2205 output "13 pin out" when only BCP power up (no VCC)?
After that, even if you turn on VCC, does RST remain LO?

Best Regards,
Hiroaki Yuyama

0 Garry Elder over 7 years ago in reply to Hiroaki Yuyama TED

TI__Intellectual 2120 points

The RST pin is controlled by the voltage applied to VCC so goes low when VCC < VPFD and goes high when VCC > VPFD + tRST. The value of VBC doesn't affect RST.

VOUT is always providing a voltage that is either VCC or VBC.

The power source is switched to BCP when VCC is less than VPFD and BCP is greater than VPFD, or when VCC is less than BCP and BCP is less than VPFD. When VCC is above VPFD, the power source is VCC.

I hope this helps.

0 Hiroaki Yuyama TED over 7 years ago in reply to Garry Elder

Expert 1730 points

Dear, Garry-san and BQ product support Team.

Thank you for your answer.
I understood the behavior of RST by VCC and BCP.
I will check that the customer does not have VOUT.

Best Regards,
Hiroaki Yuyama

Power management

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BQ2205LY: RST remains at LO