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TPS62290: Getting 2.2V on output when enable pin is 0.

Sagar Kumar
Prodigy 235 points
Part Number: TPS62290
Other Parts Discussed in Thread: TPS62740

Hi,

In our application, we need a switch which can ON our device but not able to OFF via switch if someone closed the switch(SW3). But before shipping the product we need our micro-controller should be off so that it can consume less power. Thats why we closed the switch SW3 and unplug the battery and connect the battery again. but when we plug the battery again we are able to get 3V on output via oring circuit on BUCK_EN.

Can i know the reason behind this? Without enabling buck_EN how BUCK got enable?

I did some more debugging which is as follow-

1. Remove the R83 and closed the switch SW3. 

2. Plug the battery and Switch on the device.

3. Now we closed the switch and unplug the battery 

4. After plugging the battery we are able to get 2.2V on Buck output. which should not 2.2V since in our application output volatge work as feedback for buck enable pin. thats 2.2V enable the buck.

My question is why unplugging and plugging the battery create 2.2V on output of buck while switch is in OFF state? Please provide me possible reason. 

Battery positive terminal on TP16

Battery thermistor terminal on TP61

Battery negative terminal on TP62

  • 0
    TI__Guru**** 150760 points
    You need to measure some waveforms of the key signals (Vin, Vout, EN, SW) in the circuit to see what is going on.

    And instead of the older TPS62290, you might look at the smaller TPS62233 or the more efficient TPS62740/3. The TPS6274x family has a load switch which might be useful for your purpose.
  • 0 in reply to Chris Glaser
    Prodigy 235 points
    Hi Chris,
    I permanently short EN pin with ground , Vin equal to battery voltage which is 3.7V and we are able to get 2.2V instead of 0V.

    Note: according to use case switch will be off during delivery the product to customer. So we shorted the EN pin to GND so that we got 0V on O/p but we are getting 2.2V which triggering EN again.

    So Question is ? When battery is connect , switch is in OFF condition and i shorted the EN with GND via any wire. O/P remain 2.2V
  • 0 in reply to Sagar Kumar
    TI__Guru**** 191445 points

    What other circuitry is on your board?  There may be some leakage path external to the TPS62290 that allows some portion of the input voltage to appear on the output of your TPS62290 circuit,

  • 0 in reply to JohnTucker
    Prodigy 235 points
    hi john,
    we have 3 type of voltages in the design.
    USB VBUS voltage to charge battery(VBAT_IN). TPS62290DRV used for generaate 3V from VBAT_IN.

    3V used for MCU(ATxmega128)and Accelerometer(LISD2H).
  • 0 in reply to Sagar Kumar
    TI__Guru**** 191445 points
    An MCU? That is the first place I would look for a leakage path. Can you disconnect the output of the TPS62290 and see if the 2.2 V is still there?
  • 0 in reply to JohnTucker
    Prodigy 235 points

    Hi John ,
    i will try and will let you know.

    Let assume MCU provide leakage power.
    Battery is connected and SW3 is On,
    Now i turn OFF the switch and remove the battery. After i plug the battery again. I will get 3V. Can i know since only two things provide BUCK_EN signal to buck .
    1. if i turn ON the switch which i did not do
    2. VCC_3VO itself. which will not be generated without enabling the buck.

    But still buck got enable and we able to get 3V on buck O/P. any possible causes?

  • 0 in reply to Sagar Kumar
    TI__Guru**** 191445 points
    If what I suspect is happening, the fact that you have the TPS62290 disabled is not relevant. To quickly test this, keep the switch off. remove the battery and then plug it back. If you still have voltage on the output, check the SW node waveform. If it is switching then the TPS62290 is not disabled. If there is no switching on the output, only dc voltage, then the problem is that there is a leakage path from one of your other voltage rails back to the output of the TPS62290. Most likely the leakage path is thru the MCU, but it could be some other path way. You will have to carefully disconnect each piece of circuitry one at a time until you find the leakage path. Do you understand this or do you need more explanation?
  • 0 in reply to Sagar Kumar
    TI__Guru**** 150760 points
    You need to measure some waveforms with a scope to see what is happening in the circuit.

    If the MCU is connected to the battery (or through a resistor), this voltage can flow backwards onto the 3V rail.
  • 0 in reply to JohnTucker
    Prodigy 235 points
    hi John,

    I will definitely try it and let u know. But did not understand why my logic is not relevant for disabling the buck ?

    Buck_En done by oring diode BAV23C.
    I am keeping switch off .
    Removing battery means, no power source to generate vcc_3v0.

    So buck need first triggered to generate 3V after that feedback path remain enable all the time.

    But how buck get first trigger for enable the buck?
  • 0 in reply to Chris Glaser
    Prodigy 235 points

    Hi Chris,

    Yes, we are using voltage divider on battery to measure battery voltage using MCU adc pin. I will check and will get u back about this.

    Voltage divider were providing 1.11V to that adc pin. will it causes 2,2V on 3V rail?

  • 0 in reply to Sagar Kumar
    Prodigy 235 points

    Hi Chris,

    I mounted only these components in bare pcb. when I shorted Buck_EN with gnd, VCC_3V0 goes to 0V but still when i remove the short BUCK output become 3V despite switch is in close position.

    It seems high impedance state. Can you provide possible root cause?

  • 0 in reply to JohnTucker
    Prodigy 235 points
    Hi John,



    I mounted only these components in bare pcb. when I shorted Buck_EN with gnd, VCC_3V0 goes to 0V but still when i remove the short BUCK output become 3V despite switch is in close position.

    It seems high impedance state. Can you provide possible root cause?
  • 0 in reply to Sagar Kumar
    TI__Guru**** 150760 points
    Do you have a scope with which you can measure some waveforms? This would give the actual root cause and not just theories.

    It's possible there is a wiring error on the board, solder short or open somewhere, a damaged component, coupling through the switch to EN (from the dV/dt of the battery insertion), etc.
  • 0 in reply to Chris Glaser
    Prodigy 235 points

    In Assembled PCB with MCU,accelrometer all are mounted. Vin=3.7V(DC), Buck_EN= shorted with GND so it is 0V. Vout= 2.2V which is switch between 2.2V to 2V like in atached image.

  • 0 in reply to Sagar Kumar
    TI__Guru**** 191445 points

    What does the SW node waveform look like?  Is it switching?  Have tried completely disconnecting all loads from the output?