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TPS65262-2: Expected failure part of Buck circuit.

KIM Andy
Expert 2530 points
Part Number: TPS65262-2

Hello
Our customer is applying TPS65262-2RHBR.
The applicable specifications are as follows.
VIN = 5 V
Voutput = Buck 1 / 3.3V, Buck 2 / 3.3V, Buck 3 / 1.5V
problem

1. Buck2 is Enable, but PWM output is 0V.

2. Buck3 is Enable, but 2.5V output.

Can you figure out where the two cases above can occur in the block diagram?
Please let me know what is expected.

  • 0
    TI__Expert 7500 points

    Hi Kim,

    Can you upload your SCH?

    Thanks,

    Lishuang

  • 0 in reply to Lishuang Zhao
    Expert 2530 points 
    Hello
    
thank you for your quick reply.

Attach the schematic.

    PMIC SCH.pdf

    Thank you.
  • 0 in reply to KIM Andy
    TI__Expert 7500 points

    Hi,

    1. As you said, Buck2 PWM output is 0V, it means that VCC_3.3V=0. If it is right, VCC_3.3V is the input for EN3. So why Buck3 has output 2.5V with EN=0V?

    2. Buck1's output and 2 LDOs are working well? What is the Buck1 output, 3.3V or 0.895V?

    3. Please double check R518 and R522 solder value.

    4. If all the above are double checked, please capture some waveform of Buck2 and Buck3 with VIN, Vout, SW and EN.

    Thanks,

    Lishuang

  • 0 in reply to Lishuang Zhao
    Expert 2530 points

    Hi,

    1. As you said, Buck2 PWM output is 0V, it means that VCC_3.3V=0. If it is right, VCC_3.3V is the input for EN3. So why Buck3 has output 2.5V with EN=0V?

    - 3.3V_Enable input to Buck2 Enable (8Pin) is a separate power supply from VCC_3.3V. In case of Buck3, VCC_3.3V is not output, and Buck3 output is abnormally 2.5V even though Enable low (0V). (FB resistance setting is 1.5V)

    2. Buck1's output and 2 LDOs are working well? What is the Buck1 output, 3.3V or 0.895V?

    - Buck1 and LDO 2 channels work normally. In case of Buck1, Enable operates because it receives abnormal 2.5V of Buck3. Buck1's normal output voltage is 0.9V

    3. Please double check R518 and R522 solder value.

    - Same as the schematic. Because it is 1.5V output after PMIC unit replacement

    4. If all the above are double checked, please capture some waveform of Buck2 and Buck3 with VIN, Vout, SW and EN.

    - No oscillation and nothing special for PWM normal output.

    Thanks,

  • 0 in reply to KIM Andy
    TI__Expert 7500 points

    Hi Kim,

    1. Can you try that the input voltage is 12V?

    2. If 12Vin also has the problem. please change back to 5Vin. And capture a waveform of Buck2 with EN start up, like datasheet page 25, figure 31-34? Please add a channel with BST signal. 

    3. For Buck3, can you measure EN3 pin (pin17) and FB3 pin (pin18) voltage?

    4. Have you tried change a new sample?

    Thanks,

    Lishuang

  • 0 in reply to Lishuang Zhao
    Expert 2530 points

    HI

    The requested waveforms of BUCK 1,2,3 are attached.

    Please confirm.

    TPS65262-2.xlsx

  • 0 in reply to KIM Andy
    TI__Expert 7500 points

    Hi Kim,

    From your results, all buck have desired output. So what is the input for the test, 12Vin or 5Vin? After changing to 12Vin, the issues are disappeared?

    Thanks,

    Lishuang 

  • 0 in reply to Lishuang Zhao
    Expert 2530 points

    Hi

    All were tested under 5V input conditions. The customer received a reply that the test was difficult for the 12V operation.

    Thanks,