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BQ25306: BQ25306 is used as a DCDC with VINdpm

jiangwf
Prodigy 20 points
Part Number: BQ25306

1. Input power supply, solar panels. Specification: 9-12V/2A max

2. Charging voltage preset value 8.4V

3. Output is connected to the heating plate. Specification: 8-9V/500-800mA

The reason for using this chip as a DCDC is that relying on the VINdpm of the charging IC, when the input source power is insufficient, it can limit the input source from being pulled short circuited.

Question:

1. According to the specifications, this chip has a battery detection function. The bat pin is directly connected to the heating element, and a large capacitor in parallel can be used to ensure the normal operation of the charging IC as an equivalent battery.

2. Debugging other charging chips, it was found that when the IINdpm setting is too large, the minimum charging current supported is also relatively high (such as IINdpm 3A with a minimum charging current of 1A and IINdpm 1A with a minimum charging current of 0.3A). If it is less than this value, the charging IC will intermittently switch. Currently, this IC is 3A, is there any such issue.

  • 0
    TI__Mastermind 22740 points

    Hello, 

    For 1) can you please clarify where in the datasheet you see a battery detection function? The BAT pins purpose is so the BQ25306 can measure the battery voltage, but as long as charge is enabled the device will attempt to charge the "battery" (or large capacitor). 

    I also recommend you reference figure 9-1 on page 16 of the datasheet to confirm the charging profile will work with your heating plate output. The IC will either work to regulate current or voltage depending on the voltage sensed at BAT pin. One other point, since you will not have a real battery the device will need to "soft start" when input is connected with the device initially in trickle charge phase (Itrickle is 35mA). You will need to verify if this behavior is acceptable for your load.  

    For 2)  charge current can be configured from approx. 250mA up to 3A via resistor at ICHG pin. There should not be any issue configuring charge current to a value in the range of 500mA to 800mA as your specification states. 

    Best Regards,

    Garrett