Other Parts Discussed in Thread: BQ25703, BQ25713, BQSTUDIO
Application Background :
I'm currently looking into the BQ25703A buck-boost charger-controller IC for a delayed shutdown application. We are planning to charge the super-capacitors bank to a level where it can deliver a power output of 10 W for 45 seconds.
The back up load for one case is the Raspberry Pi micro-controller, which requires an input voltage of 5V and draws a maximum current of 2A.
The back up load for another case is a cellular gateway module, which requires an input voltage of 9-30 V and draws a maximum current near to 500mA.
Thus the power requirement for both the cases is around 10-12 W for 45 seconds time period.
For the first case, we might need a buck converter to step down and regulate the super-capacitor voltage to 5V.
For the second case, we would require a boost converter to boost the voltage to ~20V.
BQ25703A :
I came across the USB OTG mode for the bq257043A, which allows us to use the super-capacitor bank as a back-up power source. In the data sheet it is mentioned :
The bq25703A supports USB OTG functionality to deliver power from the battery to other portable devices through USB port (reverse mode). The OTG output voltage is compliant with USB PD specification, including 5 V, 9 V, 15 V, and 20 V (REG0x07/06()). The output current regulation is compliant with USB type C specification, including 500 mA, 1.5 A, 3 A and 5 A (REG0x09/08()).
So, my questions are the following :
1.Can we use the bq257043A for the above mentioned application as follows ? -
-Depending on the type of load (case 1 or case 2), the voltage and current regulated values can be set using i2c, and the power requirements are matched according our needs.
-The CHRG_OK pin can be monitored for an input power shutdown, and then EN_OTG pin can be triggered to switch to OTG mode on power failure.
- The Vbus voltage and regulated current will then drive the load as a power back up for 45 seconds.
2. If the voltage of the super-capacitor / battery is less than the OTG programmed voltage, will the IC boost the battery voltage to ~20V and maintain it for the period of the application? Does it operate in the CV mode or CC mode?
3. Is the external buck-boost circuit (pins SW, LODRV, HIDRV, with transistors Q3 and Q4) available in the OTG mode as well? I understand that the buck-boost mode is for charging, but would we need to make use of that part of the schematic to buck/boost the super-capacitor voltage to our desired levels in the OTG mode? Or does the programming of the OTG registers handle the buck/boost internally?
4. Can the BQ25703A work equally well in charging a super-capacitor as it does with a Li-ion battery ?
Thank you for time.
Looking forward to your response.
Best,
Kunal
