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Original question:

LM5143-Q1EVM-2100: EVM Single output two phase sync buck configuration

LM5143-Q1EVM-2100: EVM Single output two phase sync buck (15V)

LIN YU MING
Prodigy 250 points
Part Number: LM5143-Q1EVM-2100
Other Parts Discussed in Thread: LM5143

Tool/software:

Using the LM5143-Q1EVM-2100 for the following tests:

  1. Dual outputs – FB1 connected to VDDA, FB2 connected to AGND, and MODE tied to AGND. VOUT1 and VOUT2 provided 3.3 V and 5 V, respectively.

  2. Dual outputs – R22 removed, using R21 and R30 as a voltage divider to generate VOUT1 = 15 V and VOUT2 = 5 V, with normal output operation.

  3. Single-output, two-phase synchronous buck – EVM modifications as follows:

    • FB1: DNP R22, R21 = 240 kΩ, R30 = 10 kΩ

    • FB2: Short R30

    • MODE: S2 tied to VDDA

    • SS1/2: DNP C51, short S1B

    • COMP1/2: DNP C52, C54, and R33; short S1A

    • VOUT1/2: Short R34

    • VCCX: Tied to GND

Test results:

  • VOUT only reached 1.3 V.

  • VCC, originally 5 V, dropped to 3.3 V with a sawtooth ripple.

  • VDDA dropped to 3.3 V with a sawtooth ripple.

  • SS pin output was 0 V.

After reverting to the Test 2 configuration, VOUT1 and VOUT2 became 1.3 V and 3.3 V, respectively. I am not sure why the output behaves this way.

After replacing the IC, I confirmed that the outputs matched those of Test 1 and Test 2. However, after reconnecting the Test 3 configuration, the test result was still the same: VOUT only reached 1.3 V. It is unclear why this result occurred.

  • 0
    TI__Guru* 77422 points

    Hello,

    Did you adjust anything else for test 2? If Vout1 = 15V, you'll need to update the inductor and output caps...and probably the compensation values as well.

    Please complete the LM5143 quickstart calculator for the 2-phase setup at Vout = 15V (test 3 circuit) to assist with component selection, compensation, etc. Also, you may want to reduce Fsw for lower losses.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 250 points

    Hi Tim:

      Thank you for your previous response. During Test 2, only R22 was removed, using R21 = 240 kΩ and R30 = 10 kΩ.
    I would like to confirm: if the LM5143 quickstart calculator for the 2-phase setup is not performed, would the same situation as in Test 3 occur? In such a case, could this potentially damage the IC?
    Alternatively, is there any configuration that can restore the device to normal operation?

    Your guidance on this matter would be greatly appreciated.

    Best regards,

    YUMING

  • 0 in reply to LIN YU MING
    TI__Guru* 77422 points

    Hi Yuming,

    The main item that would damage the IC is overvoltage on VCCX, but it looks like you grounded this pin. Changing to 15V will overstress the output caps, increase inductor ripple current etc, so it's better to redesign the power stage as needed.

    --

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 250 points

    Hi Tim:

     Thank you for your previous response. So was the primary cause of IC damage an overvoltage on VCCX? If so, does this mean that generally not connecting VCCX to VOUT would prevent damage?

    If we modify Test 3 to a 5 V output with the following configuration:
    • FB1: Connected to AGND
    • FB2: R30 shorted
    • MODE: S2 tied to VDDA
    • SS1/2: C51 DNP, S1B shorted
    • COMP1/2: C52, C54, and R33 DNP; S1A shorted
    • VOUT1/2: R34 shorted
    • VCCX: Tied to GND

    Would this configuration work?

    YUMING

  • 0 in reply to LIN YU MING
    TI__Guru* 77422 points

    VCCX max is 5.5V (tying this to 15V would definitely damage it).

    Send on the quickstart file for any change you want to make.

  • 0 in reply to Timothy Hegarty
    Prodigy 250 points

    Hi Tim,
    　Thank you for your response. If we have any further questions, we will post again. Thank you.

    YUMING

  • 0 in reply to LIN YU MING
    TI__Guru* 77422 points

    Thank you, Yuming.