BQ25700A: OTG

Hi Jelly,

Are you attempting to start OTG on the EVM or on a custom board?

The EVM user's guide has a procedure for starting OTG that I have tested. Even if you are using a custom board, please follow these steps as closely as possible. (pasted below for reference.)

If following this procedure works for you, then we will try to determine what is in the procedure that is not covered in the datasheet section you reference in your post. If following the procedure still does not work, we will try to determine what is different in your setup versus the EVM/setup procedure in the UG.


Here are the EVM UG steps for starting OTG:

2.4.1 Charge Function

1. Make sure Equipment Setup steps are followed.
2. Set Tgt Address to 12(9) for bq25700A or D6(6B) for bq25703A
3. Write “020E” to charge option 0 register 0x12H (bq25700A) or 0x00H (bq25703A).
Measure → V(J1(VIN)) = 10 V ±0.5 V
Measure → V(TP28(CHRG_OK)) = 3 V to 4.5 V
Measure → V(TP21(REGN)) = 6 V ±1 V
Measure → V(TP22(ILIM_HIZ)) = 2.2 V
4. Write “0800” to charge current 0x14H (bq25700A) or 0x02H (bq25703A). Turn on load #1.
Measure → V(J6(SYS)) = 8.4 V ±0.5 V
5. Turn on LOAD #2 (VBAT Load).
Measure → V(J5(VBAT)) = 7 V ±0.5 V
Measure → I(J5(VBAT)) = 2 A ±0.5 V


2.4.2 OTG Function

Use the following for OTG function settings:
1. Set EN_OTG high on J2 (EN_OTG) or short TP37 to TP35 (EN_OTG).
2. Connect a 7-V power supply to the VBAT load. Remove the VIN power supply from J1. (Connection
must be physically removed from board).
3. Write the Charge Voltage Register to 0x20D0.
4. Write “0200” to the OTG voltage register. Write “4000” to the OTG current registers.
5. Select EN_OTG in Charge Option 3.
Measure → V(J1(VIN)) = 5 V ±1 V

Regards,
Steve