BQ25505: VBAT_OK does not change (BQ25505)

Ally

Part Number: BQ25505

Tool/software:

Hi, I have designed a solar charging circuit based on BQ25505. I have connected both the primary (VBAT2 = 3.4v) and the secondary (VBAT1 = 2.4v) batteries.

The problem is that always VBAT_OK pin = 0v and the MUX does not switch from the primary to the secondary battery. (VB_PRI_ON pin = 0v , VB_SEC_ON pin = 3.4v)

I have chosen these resistors:

R_OK1 = 5.76M, R_OK2 = 6.81M, R_OK3 = 576K, R_OV1 = 6.34M, R_OV2= 6.81M

Vstor = 3.4v

What is the reason for the problem?

6 months ago

0 Michael Emanuel35 6 months ago

TI__Mastermind 40325 points

Hello,

Can you please share a schematic so I can better assist you?

Regards,

Mike Emanuel

0 Ally 6 months ago in reply to Michael Emanuel35

Prodigy 50 points

Hi Michael, This is the schematic:

Thank you in advance.

0 Michael Emanuel35 6 months ago in reply to Ally

TI__Mastermind 40325 points

Hello,

My schematic review is as follows:

1. I calculate VBAT_OV as 3.50V, VBAT_OK_PROG as 2.64V, and VBAT_OK_HYST as 2.76V.

The secondary battery is not above VBAT_OK_HYST so the mux will not switch to the secondary battery as shown in Section 7.3.5. It needs to be charged more. This is evident that VBAT_OK is low. What does the pin voltage of VBAT_SEC read? Maybe it is not making good connection?

Regards,

Mike Emanuel

Power management

Power management forum

BQ25505: VBAT_OK does not change (BQ25505)