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TPS22942: Vout not working properly

Vikas Thukuntla75
Intellectual 520 points
Part Number: TPS22942
Other Parts Discussed in Thread: TPS62740, TPS22941, TPS22924, TPS2595

Hi,

I am pursuing TPS22942 and made a circuitry (shown below) for powering on/off the supply source to a RF module. RF module takes 45mA approx. VCC_3V is the input source and VCC_3V_RF is the output. While I am making RF_POWER_ONOFF='0', VCC_3V_RF is going to 3V. However it is going to 2.3V approx while RF_POWER_ONOFF='1'. Below is the waveform. I am fine with the RF_OCn behavior as shown in below waveform. Also I have measured that VIN voltage is steadily 3V at all times (no spikes/dips).

I checked the behavior of RF module with another circuitry that has a switch. Basically I used a voltage regulator TPS62740, and controlled its CTRL pin for powering on/off the supply source to RF module. The LOAD output from this regulator is properly powering on to 3V and powering off to 0V. So, there does not seem to be any issue with the RF module.

I have also checked the above TPS22942 circuitry behavior without any RF module connection. Then, the switch seems to behave as intended. VOUT is going to 0V when it is switched off.

I don't think the above abnormal behavior of TPS22942 is due to output/input capacitance values, because the output remains at 2.3V continuously. Not sure if I am missing something in its behavior. Kindly suggest why TPS22942 is behaving as above, and how can its VOUT behave appropriately. Kindly let me know if you need any further info from my side.

Thanks & Regards,

Vikas Chandra Rao.

  • 0
    TI__Genius 10855 points

    Hi Vikas, 

    Thanks for reaching out on E2E!

    Can you elaborate on the output load while the load switch is on? Is the output load resistive, or just your load capacitance?

    The reason why I'm asking is because the TPS22942 doesn't have a output discharge feature (QOD) to pull down the output of the switch when the device is off. This means that if your load isn't dissipating the capacitors, they will remain high when the switch is off. This is probably why the switch works disconnected from the load, since there isn't any output capacitance to hold up the output. 

    Can you try adding a resistive load to the output and seeing if it discharges? 

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Intellectual 520 points

    Dear Arthur,

    Our output load is basically an RF module. So, it is mainly a capacitive load. I have tried adding a resistive load of 100ohm and 47ohm separately, to the existing load. I observed that the VOUT reduces to 1.1V and 720mV approx (below waveforms), whenever it is switched off. As you mentioned, RF module (load) does not seem to dissipate its capacitors.

     

    Our device is a battery operated one. So, I cannot use any resistive load. However I want your suggestion/clarification on few things as below.

    1. Is it fine if VOUT stays at some intermittent voltage whenever it is switched off? Does it not affect the capacitive load (like our RF module or any other load) or TPS22942 in the long run?
    2. If I have to dissipate the output voltage whenever it is switched off, can you suggest any mechanism so as to make VOUT=0V?
    3. Do you have any switch (equivalent to TPS22942) with QOD feature?
    4. RF module is connected to TPS22942 through a cable. So, I want to protect VOUT (from shorting to GND, etc) and in-turn protect TPS22942. Can you suggest any protection mechanisms/devices that I can pursue using with TPS22942? (Just to let you know, I have tried all my above experiments without cable)

    I am also pursuing TPS22941 for another circuitry where-in VOUT is behaving similarly as above (below waveforms for your reference). So, I wanted to check whether there is no issue if VOUT has such intermittent voltage, and it does not affect any capacitive load. Kindly clarify and suggest.

     

    Thanks & Regards,

    Vikas Chandra Rao.

  • 0 in reply to Vikas Thukuntla75
    TI__Genius 10855 points

    Hi Vikas, 

    Thanks for being patient as many of us are returning from vacation. I appreciate the detailed oscilloscope shots and summary! Please find the answers to your questions below:

    1. Is it fine if VOUT stays at some intermittent voltage whenever it is switched off? Does it not affect the capacitive load (like our RF module or any other load) or TPS22942 in the long run?
      1. If VOUT is at an intermittent voltage, it won't affect the TPS22942 in any adverse way. However, I can't say for sure regarding your RF module.
    2. If I have to dissipate the output voltage whenever it is switched off, can you suggest any mechanism so as to make VOUT=0V?
      1. You could include an external pull-down circuit, similar to one shown below. However, you would need to connect an external GPIO to the gate of the external FET.  
    3. Do you have any switch (equivalent to TPS22942) with QOD feature?
      1. We have switches similar to the TPS22942 with the integrated QOD feature, but without the current limit functionality.
    4. RF module is connected to TPS22942 through a cable. So, I want to protect VOUT (from shorting to GND, etc) and in-turn protect TPS22942. Can you suggest any protection mechanisms/devices that I can pursue using with TPS22942? (Just to let you know, I have tried all my above experiments without cable)
      1. When an overcurrent event occurs, the TPS22924 will operate in constant-currnet mode to protect the RF module and itself. If you're looking for additional protection features including overvoltage protection, undervoltage lockout, and thermal shutdown, I recommend looking at our eFuses, including the TPS2595.

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Intellectual 520 points

    Dear Arthur,

    Thanks for your clarifications. I will be unable to provide an extra GPIO just for QOD. I saw TPS2595 eFuse. Looks like QOD and Fault notification are complementary (both not available at same time). I will continue pursuing TPS22942 for now. Based on testing, if I have to use any protection, I will come back to you. Just in case, you make any switches in future similar to TPS22942 with QOD, kindly let me know.

    Thanks & Regards,

    Vikas Chandra Rao.