BQ25505: the questions about VBAT_OK signal

James,

What voltage thresholds did you design for and what are the resistance values you chose for your resistor network?

Thanks,

Ricardo 

Ricardo,

The voltage threshold is designed as follow:

1. Vbat_ok_prog = 4.0V ;

2. Vbat_ok_hyst = 4.2V ;

3. Vbat_ov = 4.2V ;

I chose the resistance values for resistor network as follow:

1. Rok1 = 3.74M , Rok2 = 8.66M , Rok3 = 470K ;

2. Rov1 = 5.76M , Rov2 = 7.5M ;

3. Rok1 , Rok2 and Rov1 are divided into 4 resistors and Rok3 is divide into 2 resistors because the suppler could not offer the resistances values exactly. I decided to divide them to satisfy my needs.

Although I set the resistance values as the same as BQ25505EVM-218 exactly, the VBAT_OK pin was signaled as impulses.

Thanks,

 James

James,

I am concerned that your VBAT_OK is equal to your VBAT_OV value as VBAT_OK must be less than VBAT_OV and greater than VBAT_UV. Resistors are not perfect and can vary by a tolerance set by manufacturing and environmental factors. I strongly suggest you lower your threshold to be within the operation conditions mentioned in the datasheet. 

However if you are still seeing this issue with EVM thresholds set, then there may be another issue. Could you provide the following details?

- What are you using to power VIN?

-What is your energy storage device at VSTOR?

-Could you provide an oscilloscope shot of VIN, VSTOR, and VBAT_OK as VSTOR is rising?

Thanks,

Ricardo