BQ25730: BQ25730 About the function

In the above situation, I am wondering if it is possible to output the batter voltage to vsys.

Hi Lee,

Thanks for reaching out.

When USB C is connected, I would expect the input to be between 5 V to 20 V depending on the availability of Power Delivery.

Vsys will be regulated and is set by VSYS_MIN register REG0x0D/0C(). If Vsys if too low, you can always adjust it.

This is from section 9.4.1.1 (pg 39) of the datasheet.

"The device employs Narrow VDC architecture (NVDC) with BATFET separating the system from the battery. The minimum system voltage is set by VSYS_MIN register REG0x0D/0C(). Even with a depleted battery, the system is regulated above the minimum system voltage. When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode), and the system is regulated at VSYS_MIN register value. As the battery voltage rises above the minimum system voltage, system voltage is regulated 150 mV above battery voltage when BATFET is turned off (no charging or no supplement current). When in charging or in supplement mode, the voltage difference between the system and battery is the VDS of the BATFET and the BATFET is fully on. "

This paragraph describes the behavior of VSYS and VBAT at different states.

Thanks and hope this helps,

Peng

*If my answer solves your question, please press "This Resolved My Issue" on the thread. 

Thanks for the answer

Assuming the USB C adapter power is 5V 1A, 

If vsys_min is set to 20V, there is insufficient current to operate the product.

At this time, you mean that insufficient current can be drawn from the battery??

Or,When the 24V adapter is connected, 

if you connect the BQ25730 VSYS to the low power IC and connect the 24V adapter power directly to the high power IC, 

will the charging current increase when not in operation and the charging current decrease when operating??

Hi Lee,

I don't quite understand your second follow-up question about 24 V adapter and low power vs high power IC. Can you clarify? 

I hope the following will address your questions.

This is from section 9.3.17 (pg 33) of the datasheet:

"The charger supports Dynamic Power Management (DPM). Normally, the input power source provides power for the system load and/or charging the battery. When the input current exceeds the input current setting (IIN_DPM), or the input voltage falls below the input voltage setting (VINDPM), the charger decreases the charge current to provide priority to the system load. As the system current rises, the available charge current drops accordingly towards zero. If the system load keeps increasing after the charge current drops down to zero, the system voltage starts to drop. As the system voltage drops below the battery voltage, the battery will discharge to supplement the heavy system load."

In other words, yes, if your input source cannot provide the power level to maintain system load, then the battery will discharge to supplement the load. Keep in mind that in supplement mode, VSYS will not be the VSYS_MIN value set in the register and the voltage difference between the system and battery is the VDS of the BATFET (BATFET is fully on, discharging from battery to VSYS).

If you want to boost from 5 V USB-Type C input to 20 V, keep in mind that it will only work in the 5S configuration as the other configuration will trip the SYSOVP setting of the IC.

Thanks,

Peng

*If my answer solves your question, please press "This Resolved My Issue" on the thread. 

Thanks for the answer

It was a perfect answer.

HI

I'll just ask you one more question.

This is from section 9.3.1 of the datasheet

Does the above mean that VSYS outputs battery power even if I2C does not work?

Hi Lee,

Yes, in the absence of VBUS, battery will discharge to VSYS to power the system

The IC's internal registers are defaulted to a reset value. I2C is only used to provide flexibility and to update or change those values. As a matter of fact, in the above scenario, battery will provide system power if VBUS is not present. But as soon as VBUS is present, VBUS will provide power to the system. However, if you do not have I2C in the system, then you will not be able to charge the battery as the charge current (0x02/0x03) defaults to 0 A. If you can't charge the battery, then it defeats the purpose of having a battery charger.

If you are interested, we have the EVM for evaluation.

https://www.ti.com/tool/BQ25730EVM 

Thanks,

Peng

*If my answer solves your question, please press "This Resolved My Issue" on the thread.