Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 167 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ24075: Battery backup for data gathering device

Doug Brouwer
Prodigy 10 points
Part Number: BQ24075
Other Parts Discussed in Thread: BQ25155,

Our device normally runs on line power, but we want it to continue to operate, in the event of a power outage, for a fairly short period of time to continue to gather data. So we are trying to design a battery backup. When the battery voltage drops to something around 3.5 to 3.7V, we want the device to power down completely, and not continue to drain the battery. We have searched for a component solution, but the best we have come up with is the BQ24075. The issue with this design is that the battery will continue to be drained by U5, a TPS3840PL or TPS3840DL.

1. Does this circuit look good?

2. Can you suggest a better way to accomplish what we are trying to do?

  • 0
    TI__Mastermind 23220 points

    HI Doug,

    Welcome to E2E!

    Doug Brouwer said:
    1. Does this circuit look good?

    On the charger specific portion, I do see that the TS pin is set for a voltage divider but is pulled up to the BAT pin, is there a particular reason for this? This will cause the TS voltage to change as battery changes. If you're not using the TS functionality (as you have the 200kOhm and 49.9kOhm voltage divider), this needs to be pulled up to VIN. 

    For the IN pin, I do see missing capacitance (1uF to 10uF) that is needed. On the OUT pin, it is recommended to keep the capacitance between 4.7uF to 47uF but I don't see an issue with the 100uF capacitor. 

    As for this low Iq battery usage that utilizes the SYSOFF, the HXY2300AI, and TPS3840PL/DL, this looks good but there is a state I cannot guarantee the behavior. In the case that the HXY2300AI is pulling SYSOFF to GND (RESET on TPS3840PL is LOW), this leaves SYSOFF floating and this is not recommended. 

    Doug Brouwer said:
    2. Can you suggest a better way to accomplish what we are trying to do?

    Do you perhaps have a microcontroller in your system since this is a data gathering device? I can imagine using the BQ25155 to achieve this without needing any external parts. 

    The following would be changed:

    • OUT pin on BQ24075T -> PMID pin on BQ25155
    • Access to ADC within charger that can monitor the battery voltage
    • When battery voltage falls below 3.5 V (or whichever voltage that you device 3.5V - 3.7V), you can change the put the device into shipmode for a 10nA battery Iq

    Best Regards,

    Anthony Pham