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LM5141QRGEVM: The board cannot output 5V @1A with the default setup

Shawn Ding
Expert 3190 points
Part Number: LM5141QRGEVM
Other Parts Discussed in Thread: LM5141-Q1

Hi Team,

I am using LM5141QRGEVM to produce 5V supply voltage, with maximum load 7A.

The input is 19V power supplier.

However, with the default setup as described in user guide, the voltage will go down to 2.85V when connecting the 1A load.

But the output is normal in below two conditions.

1) when disconnect the load, the output will be 5V

2) when change the J9 connection, set the output 3.3V, the output is normal no matter there is load or not.

could you help on this? which reasons will cause this issue?

Regards,

Shawn.

  • 0
    TI__Expert 6860 points
    Shawn ,

    Is your input power supply getting current limited ?

    Further please ensure that the factory default setting , as mentioned in Table 2 , is followed for evaluation of 5V output on EVM

    ---Ambreesh
  • 0 in reply to Ambreesh Tripathi
    TI__Expert 3190 points
    Hi Ambreesh,
    thanks for your help.
    I tested the board with factory default setting.
    I used the power supply with 7A current limitation, It may not be limited. And from my experience, if the current be limited, the supply voltage will be forced to drop down, is this right?

    Thanks and best regards,
    Shawn.
  • 0 in reply to Shawn Ding
    TI__Expert 6860 points
    Shawn,

    Can you take the waveform of input voltage , output. Voltage and SW node and share it here .

    Ambreesh
  • 0 in reply to Ambreesh Tripathi
    TI__Expert 3190 points

    Hi Ambreesh,

    please find the waveform below.

    When use power source directly supply for the load, the voltage and the current is shown in below waveform

    When use the EVM to supply for the load, the curves are shown as below.

    And below is the waveform with SW and vin.

    Thanks and best regards,

    Shawn.

  • 0 in reply to Shawn Ding
    TI__Expert 6860 points
    Shawn ,

    Their is a current overshoot on the E load ( upto 8A ) and it doesn't reduces the current quickly enough so that the low side current limit is not triggered . Just to verify this issue , can you please test the board on resistor load ? Also another thing you can do is to first enable the device and afterwards connect the load to see if you are seeing he similar issue .

    --Ambreesh
  • 0 in reply to Ambreesh Tripathi
    TI__Expert 3190 points

    Hi Ambreesh,

    I think it is not the E load problem, with 1A load, the curve will be like this.

    I have tested, the problem still be there. and I forgot to point out

    also I think it is not an efficient way, could you check your idea on your side?

    Regards,

    Shawn.

  • 0 in reply to Shawn Ding
    TI__Guru 65357 points
    Hi Shawn,

    The LM5141-Q1 EVM is rated for 5A DC load (see EVM user's guide snvu522). Based on the 68nF soft-start cap, the output voltage ramp rate sets the current to charge the output caps. A 9mOhm shunt sets a current limit of 8A peak inductor current, and the remaining current is provided to the load.

    Please test with a resistive load to avoid current overshoots that can happen with an e-load.

    Regards,
    Tim