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BQ24075T: Inquiry on how to use BQ24075T SYS_OFF.

Part Number: BQ24075T

Hi, TI expert

A customer is developing a device using the BQ24075T.

Customers want to prevent battery discharge by using SYS_OFF until the product is opened after mass production.

Please check the information below and reply.

1. The device charges the battery with USB 5V, the battery is removable.

2. When a charged battery is inserted, SYS_OFF is set to LOW and the FET is turned on to output OUT, but the CPU boots and takes control only when it receives OUT.

Q1) I think it should be a structure in which the CPU operates while pressing SYS_OFF using a separate key, and the CPU has the SYS_OFF port control right again. Is this correct?

Q2) Is there any other way?

Q3) If there is no TEMP circuit inside the battery, can you check the R value of the TS port divider circuit? (VIN is 5V.)

Please check.  Thank you.

  • Hi Grady,

    Based on your first and second questions regarding CPU operation while pressing SYS_OFF using an external push button, I think that you may find this application note of interest. The application note also includes implementation suggestions for ship mode using a push button and a GPIO.

    If this application does not require the battery temperature monitoring function, we recommend setting the resistor that is currently set to 13k Ohms to be 200k Ohms and the resistor that is currently set to 10k Ohms to be 49.9k Ohms. This will set the voltage at the TS pin in between the hot and cold ranges which are percentages of the Vin value. Please reference section 8.5’s “Battery – Pack NTC Monitor” portion on page 9 and section 9.3.12 on page 20 of the BQ25075T datasheet for more information.

    If you would like to monitor the battery temperature, we recommend the NTC (103AT-2) resistor. Please reference section on page 25 in the BQ25075T datasheet for more information.

    BQ25075T datasheet