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BQ25713: VSYS vs VBUS in BQ25713

reza nouriyan
Prodigy 100 points
Part Number: BQ25713

Dear sir or madam

i am using BQ25713 in order to charge my 4Cell li-po batteries and also to power my system.

as i understand from datasheet we have to do these steps after POR:

1- set two resistor with ratio of 0.75 at CELL_BATPRES pin18 in order to say we have 4cell (we choosed 100k and 300k res)

2- set charge current in reg 02h and 03h

3- MAXChargeVoltage registers default values are ok to me.

4- set ADC register 3Bh and 3Ah in order to be able to read adc values

i need 12v for driving my DC motor and also 5v and 3v for my circuit

if these assumptions are ok my questions are:

1- can i give VBUS and VBAT with back to back diodes to down converter regulators and regulate my voltages to 12,5 and 3v?

2- what is difference if i give VSYS and VBAT to regulators?

3- how can i be sure that input voltage of my regulator in not coming below 12v? (can i do it by MinSystemVoltage Register 0Dh and 0Ch)

4- how can i limit input current of system?

i know i asked many questions but as always your answer will definitely help

best regards

  • 0
    TI__Expert 3320 points

    Hi There,

        Your understanding is correct.

    1- can i give VBUS and VBAT with back to back diodes to down converter regulators and regulate my voltages to 12,5 and 3v?

        FB: Nope, It is recommended to utilize VSYS to provide power to motor and  down converter regulators. Because only in this way, charger can achieve its full feature and protection function for both VBUS input side and VBAT battery side.

    2- what is difference if i give VSYS and VBAT to regulators?

        FB: By providing power to load through VSYS, charger will deliver power to regulator mainly from adaptor and battery should only supplement system when adaptor is fully loaded. This is defined to save battery life time. However if VBAT is used to power regulator then battery will keep discharging for load which is not good for battery life. On the other hand, battery discharge current is monitored through battery charge resistor RSR and if regulator is directly connected to VBAT then charger is not able to sense the real battery current and accordingly IBAT monitor, discharge current protection and system power monitor would not work properly.

    3- how can i be sure that input voltage of my regulator in not coming below 12v? (can i do it by MinSystemVoltage Register 0Dh and 0Ch)

        FB: Correct, the MinSystemVoltage setting is the value charger can guarantee for minimum system voltage value. 

    4- how can i limit input current of system?

        FB: You can do it in two ways register setting or hard ware pin. By configuring REG32[7], you can choose the effective current limit setting approach.


                Register method:  Configure REG32[7]=0 and REG0x0F/0E setting will determine the final current limit value.

                Hardware pin method: Configure REG32[7]=1 and make sure REG0x0F/0E value is higher than target current limit setting. Then configure ILIM_HIZ pin voltage based on target current limit setting below.
       

               Regards

  • 0 in reply to Shishuo Zhao
    Prodigy 100 points
    Thanks for reply Do i have to use VBAT and VSYS with back to back diodes to provide system power or VSYS only is enough. As most of the times batteries will provide power of system and adapter is not present. Adapter is used to charge batteries only.
  • 0 in reply to reza nouriyan
    TI__Expert 3320 points

    Hi There,

         You don't need add additional diodes. As only as the BATFE is included in the system shown below, BQ25713 has power path management feature, it will automatically determine which power path is chosen to power the VSYS. 

         When adapter is not plugged, battery will supplement VSYS and provide power to the system.

         When adapter is plugged, battery will be charged and adapter will power VSYS. If adapter is overloaded, for example IINDPM or VINDPM is triggered, then battery will reduce charge current or even supplement system automatically. 

    Regards

    Shishuo