BQ25173: BQ25173 circuit review and voltage inquiry when supercap is charged

Hello

ByeongTaek Oh said:

1. When charging at 5V, what is the final voltage when the Supercap is fully charged?

Based on the setting of FB pin and R78/R79 the final charge voltage will be 4.8V.

Note that as Vin-Vout decreased the output current will also decrease.  See Tabel 6-6 Page 8 of Datasheet.

ByeongTaek Oh said:

Please check if there are any issues with the circuit.

The balance resistors R82 and R83 look a little low in value, 330k would be a typical value.

Rest of circuit looks good.

1. When the supercapacitor starts charging from 0 V, could the current not reach 800 mA due to overheating of the BQ25173?

- It's currently connected via wiring, not mounted on the PCB.

2. When Vin is 5.0 V, can I charge R78/R79 to 4.979 V by setting the resistance values ​​to 210 kΩ and 40.2 kΩ?

Hello

ByeongTaek Oh said:

1. When the supercapacitor starts charging from 0 V, could the current not reach 800 mA due to overheating of the BQ25173?

- It's currently connected via wiring, not mounted on the PCB.

The BQ25173 has thermal regulation that will prevent overheating by reducing output current.  With a large voltage drop across the device, Vout = 0V the power dissipation will be high and unit enters thermal regulation.

ByeongTaek Oh said:

2. When Vin is 5.0 V, can I charge R78/R79 to 4.979 V by setting the resistance values ​​to 210 kΩ and 40.2 kΩ?

This is correct setting for 4.979V.  But with 5V input the Vin-Vout will be near 0V and unit will enter sleep mode.  The first resistor setting for 4.8V is a better configuration.