Other Parts Discussed in Thread: LM234
Hi,
We are using BQ24650RVAT in our design for the Solar charging of a 2 cell Lithium ion battery . The design parameters are as follows:
- Vin : 18 V - 26V
- Vout (Charging voltage): 8.4 V
- Charging current (I_charge) : 4 A
We have a number of units working fine in the field. But one of the unit stopped charging even though the valid input voltage is available from the solar panel with STAT1 and STAT2 leds in OFF state. As per the datasheet, this means that Charge is suspended due to Overvoltage, sleep mode or battery being absent. But none of the above conditions seems to be valid.
In-order to diagnose the problem, we connected the device to a power supply with 21 V output. The observations / measurement at various pins of the BQ24650RVAT is as follows:
- Power supply input voltage: 21 V
- Current drawn from the power supply : 6 mA
- Voltage at the +ve terminal of the battery : 7.1 V
- MPPSET voltage : 1.2V
- Vref: 3.3V
- RegN: 6V
- TS: 2V
- VFB: 3.6 V ( which is really abnormal as it should be < 2.1V)
We tried to power cycle the BQ24650RVAT to fix the issue by removing the Battery and input power supply but it was not successful.
What is surprising is that the unit was working good in the field for a couple of days, before encountering this problem. Moreover all the conditions for the battery charging (as stated below) are met but the battery is not being charged:
• Charge is allowed (MPPSET > 175 mV)
• Device is not in under voltage lockout (UVLO) mode and VCC is above the VCCLOWV threshold
• Device is not in SLEEP mode (that is, VCC > SRN)
• VCC voltage is lower than AC overvoltage threshold (VCC < VACOV)
• 30-ms delay is complete after initial power-up
• REGN LDO and VREF LDO voltages are at correct levels
• Thermal Shut (TSHUT) is not valid
• TS fault is not detected
The only anomality we observe is VFB pin stuck at 3.6V.
Any suggestions from TI experts to resolve this issue. Your help would be greatly appreciated.
Regards,
Ajay
