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TPS2121: Power channel switching drop issue

Roy Chen52
Intellectual 395 points
Part Number: TPS2121

Dear Sir,

The following is a description issue of TPS2121, whether there is a way to improve the voltage drop phenomenon caused by switching power channels, thank you!

IN1: VBATT_IN1 is in the range of 3.3V~4.2V.

INT2: VBAT_SYS is in the range of 3.3V~4.25V.

PR1: SYS_3V3 is always power on, BATT_ID_PRI is the battery ID pin of INT2 (VBAT_SYS), which is the signal of 10K resistor to ground.

BATT_ID_PRI and INT2 (VBAT_SYS) are in the same state, that is, INT2 is in place, that is, BATT_ID_PRI is in place, and INT2 is not in place, that is, BATT_ID_PRI is not in place.

OV1: AP_USB_VBUS is determined by whether or not USB is inserted. When USB is plugged in, the voltage is 2.7V; USB is not plugged in, the voltage is 0.

CP2: SYS_3V3 is always powered, CP2 voltage is 1.96V for a long time.

OV2: Ground

OUT1/OUT2: Four 22000nF capacitors are placed on the line

SS: Connect 1000nF capacitor

ILIM: Connect 22K resistor

The logic in the red box below implements the active/standby switchover:

INT2 is connected to the main power, and INT1 is connected to the backup power.

1) When the main power is in place, PR1 is 0.42V, and the output is IN2.

2) When the main power is not in place, PR1 is 3.3V, and the output is IN1.

3) When USB is plugged in, OV1 is 2.7V and OV2 is 0V. At this time, the output is IN2 and will not switch to INT1.

The current phenomenon is:

When the main power is pulled out, when the main power is switched to the backup power, the output voltage is dropped.

When the direction of the main power is different, the battery ID and the main power supply INT2 may be disconnected from the connector.

Main battery connector Pin definition and actual position map:

The following oscilloscope measurement waveform are shown:

yellow for the battery ID and blue for the TPS2121 output.

1) When the left side of the connector above is detached, the TPS2121 output has a drop voltage.

2）When the connector on the right side of the above figure is detached first.

There is no drop voltage.    

  • 0
    Intellectual 395 points

    Dear Sir,

    Fill in the schematic and waveform...

    The logic in the red box below implements the active/standby switchover:

    INT2 is connected to the main power, and INT1 is connected to the backup power.

    1) When the main power is in place, PR1 is 0.42V, and the output is IN2.

    2) When the main power is not in place, PR1 is 3.3V, and the output is IN1.

    3) When USB is plugged in, OV1 is 2.7V and OV2 is 0V. At this time, the output is IN2 and will not switch to INT1.

    The current phenomenon is:

    When the main power is pulled out, when the main power is switched to the backup power, the output voltage is dropped.

    When the direction of the main power is different, the battery ID and the main power supply INT2 may be disconnected from the connector.

    Main battery connector Pin definition and actual position map:

    The following oscilloscope measurement waveform are shown:

    yellow for the battery ID and blue for the TPS2121 output.

    1) When the left side of the connector above is detached, the TPS2121 output has a drop voltage.

    2）When the connector on the right side of the above figure is detached first.

    There is no drop voltage.    

  • 0
    TI__Genius 13760 points

    Hi Roy,

    Thank you for reaching out to the E2E Forum.

    In order to provide a proper suggestion I would like to get some clarification on the set up and the waveform images.

    • Could I get a clarification on the circuit implemented on PR1. How is PR1 receiving 3.3V when the main power is not in place? How is PR1 seeing 0.42V when main power is in place?
    • In the sentence where you say main power and battery ID can be disconnected you mention something about the main power having a different direction. Could you explain this?
    • By left side of the connector you mean Battery ID was disconnected and then VBATT of the main power supply?
    • By right side of the connector was VBATT disconnected and then Battery ID was disconnected?
    • In the waveform is the yellow ID signal measuring PR1?

    I would also like to state that the TPS2121 is a power mux that was designed to give priority to IN1 in typical applications. You can accomplish this with the voltages from IN1 and IN2 and set voltage dividers to give signals to PR1 and CP2. If you look at section 10.3 of the TPS2121 datasheet you can look at a configuration for fast switchover that minimizes the voltage drop.

    Regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Genius 13760 points

    Hi Roy,

    I haven't heard from you in a few days. I'm hoping you were able to solve the problems with the TPS2121. If you have any more questions feel free to reach out.

    Regards,

    Andy Robles

  • 0 in reply to Andy Robles
    Intellectual 395 points

    Hi Andy,

    Reply is as follows:

    • Could I get a clarification on the circuit implemented on PR1. How is PR1 receiving 3.3V when the main power is not in place? How is PR1 seeing 0.42V when main power is in place?

    Ans: 3.3V of PR1: The switched power supply is converted to 3.3V by the LDO level. Measuring 3.3V with an oscilloscope is a long-term stable power supply.

    0.42V of PR1: After the battery is in place, the battery ID has a 10K resistor to ground, and 3.3V is 0.42V after 68K and 10K partial pressure.

     

    • In the sentence where you say main power and battery ID can be disconnected you mention something about the main power having a different direction. Could you explain this?
    • By left side of the connector you mean Battery ID was disconnected and then VBATT of the main power supply?
    • By right side of the connector was VBATT disconnected and then Battery ID was disconnected?

    Ans: VBATT and battery ID are on the same battery connector. The connector has 4 pins, the battery ID is in the middle, and both ends are VBATT and GND.

    There may be two kinds of conditions when plugging and unplugging: (1) VBATT first deviates from PIN with battery ID; (2) VBATT and battery ID are separated from PIN at the same time.

    • In the waveform is the yellow ID signal measuring PR1?

    Ans: Yes! The yellow waveform is the signal on PR1 (ie battery ID)

  • 0 in reply to Roy Chen52
    TI__Genius 13760 points

    Hi Roy,

    From what I'm seeing in the first waveform, when you disconnect the main power supply (IN2) the device notices this with the internal comparator and does a slow switchover over to IN1.

    In the second waveform, PR1 first increases greater than VREF. This makes the device go into XCOMP mode where PR1<CP2 for a instant. Then PR1 increases greater than CP2 and gives priority to IN1.

    In order to do fast switchover to reduce the voltage dip you must operate in these 2 modes only:

    In order to accomplish this you can connect main power supply to IN1 and do a voltage divider into PR1 that is greater than CP2.

    Then connect back up power supply into IN2 and do a voltage divider into CP2 that is less than PR1 but greater than VREF.

    In these modes when the main power supply is connected (IN1), PR1 is greater than CP2 so output is main power supply.

    When the main power supply is disconnected PR1 will be less than CP2 and back up power supply (IN2) will be the output.

    If you look at section 10.3 of the TPS2121 datasheet you can look at this configuration with more detail.

    Let me know if you have any questions.

    Regards,

    Andy Robles