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TPS25942L: TPS25942L operation inquiry

Grady Lee
Genius 4085 points
Part Number: TPS25942L

Hi, TI expert.

The customer applied TPS25942L to configure the circuit and set the following conditions. (Refer to attached Excel sheet and schematic)

TPS2594x-Calculation Sheet V1p0_210525.xlsx

The customer's expectation was that the input voltage would operate normally between 4.5V and 5.5V.

However, when the actual input voltage is supplied, it operates normally only when 5.1V or more is input, and the On/Off operation is repeated at a voltage below that.

I am curious about the solution to this phenomenon.

Q1) Please review which part is wrong in the schematic below.


Q2) Is there any wrong part in the calculation formula in the attached Excel sheet?


Q3) If there is no problem in schematic, why does this phenomenon occur? Please let me know if there is a solution.

Please Check. Thank you.

  • 0
    TI__Mastermind 36710 points

    Hi Grady,

    Thanks for reaching out to us. Please could you share the following waveforms during startup at input voltages of 5.1 V or more and less than 5.1 V.

    1) Input voltage, 2) Input current, and 3) Output voltage

    Kindly let us know the correct values of output or load capacitance (Cout) and load at startup (Rlstart). If the load at startup is a constant current load, please mention that value also. Please make sure that the components values in the attached schematic are as per the actual PCB, which is being used to capture the startup waveforms. 

  • 0 in reply to Avishek Pal
    Genius 4085 points

    Hi, Avishek

    We will share your inquiry.

    1. Please could you share the following waveforms during startup at input voltages of 5.1 V or more and less than 5.1 V.
    1) Input voltage / 2) Input current / 3) Output voltage

    → Please check the attached waveform. (See attached Excel)

    Iin, Vin, Vout _ Waveform.xlsx

    2. Kindly let us know the correct values of output or load capacitance (Cout) and load at startup (Rlstart).

    → Cout : 10uF(16V / 10% / X5R / 3216 ) * 2

    → Rlstart : Customer not sure. Excel-Calculation sheet says that it is 120 ohm, but I did not alculate it according to this value.

    3. If the load at startup is a constant current load, please mention that value also

    → It is not a constant current load. When the power is stably turned on, there is a CPU to start booting.

    4. Please make sure that the components values in the attached schematic are as per the actual PCB, which is being used to capture the startup waveforms. 

    → Yes,  This is the value currently applied to the actual PCB.

    Please check the attached waveform and answers to the questions, and review the three questions (Q1~Q3) that you first asked.

    Thank you.

  • 0 in reply to Grady Lee
    TI__Mastermind 36710 points

    Hi Grady,

    Please share the input current waveform as shown in Figure 61 and 62 in the datasheet. I'd like to see that the device is unable to do the startup due to thermal shutdown or current limit. Please try to adjust the value of C3 (lower and higher) and check whether startup is happening or not. EN/UVLO threshold voltage, rising (max) is 1.01 V. According the resistor divider network as shown in the schematic, less than 4.88 V leads to UVLO. Please check the voltage between Pin 14 and GND. 

  • 0 in reply to Avishek Pal
    Genius 4085 points

    Hi, Avishek

    I will reply after confirming with the customer.

    Thank you.

  • +1 in reply to Grady Lee
    Genius 4085 points

    Hi, Avishek

    The customer said it was resolved.

    Thank you.