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.

Problems with the TPS2115APW and TPS61200

Other Parts Discussed in Thread: TPS61200, BQ24075, BQ27441-G1

Hello,

I am having a few issues with one of my designs. I have a two separate Lithium ion batteries connected to a power mux(TPS2115APW ). There are a few other blocks before this(battery charger, health monitor, reverse polarity, push button controller), but this section of the circuit is where I am having problems. The output of the mux goes to a 5V DC-DC (TPS61200). The circuit works fine down to a battery voltage of about 3.3V at which case there seems to be a 1V drop across the mux. With this drop the input voltage of the DC-DC is 2.09V, and the regulator cannot successfully regulate at 5V(It drops to 4.09V). At battery voltages higher than 3.3V, the drop across the mux is negligible. Attached is a block diagram with the measure voltages at the different stages of the circuit:


Please let me know if you need more information or if you have anything you would like me to try.
Thanks, 

Felipe Ocampo

  • Hi Juan,

    What is the current measured current through the PMUX during this voltage drop condition? Is the PMUX in current limit? Thanks!

  • Hey Darwin, 

    Thanks for the response. I replaced the Rilim resistor with a 0 ohm resistor so it should not be in current limit mode.

    In working state, with a BAT2 input of 3.4V(BAT1=0V) the current draw at BAT2 is about 380mA. In a non-working state, with a BAT2 input of 3.2V(BAT1=0V) the current jumps around a lot(from 200 to 400mA). It is very hard to measure the current just going into the PMUX since I have a PCB and would need to rip up traces to add an inline resistor to measure the current. 

    By the way, the battery charger that I am using is BQ24075 and the health monitor is BQ27441-G1. In case that helps debug this issue.

    Do you think that even though we have a almost 3V at the input of the mux we are potentially not getting enough current? If so, what could be causing this? Maybe the power planes, current trace widths and copper density that I chose prior to the input of the mux? I can email you my schematics and board layout if that helps debug this issue.

    Thanks for your help ,

    Felipe 

  • Hi Filipe,

    It sounds like the PMUX is operating it's recommend operating conditions so the issue may be coming from the front end circuitry. To verify this, can you use a bench power supply to power the input to the PMUX to 2.98V (rather than the health monitor) to see if the large drop failure still occurs? If it does, can you try disabling the boost converter (just to see if their are high current short transients on the DCDC input that might be causing the drop)?
  • It looks like the reverse battery mosfet that I chose had a gate voltage that was around 3V which was the same as my input voltage. This caused the mosfet to switch between states and I guess prevented the mux from receiving enough current. The solution was switching the mosfet for one with a lower gate voltage.

    Thanks Darwin!