• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 62 subscribers
  • Views 120 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMQ61460:Output voltage problem

BONG HYUN KANG
Prodigy 10 points
Other Parts Discussed in Thread: LMQ61460, LMQ61460EVM

부품 번호: LMQ61460

This is a circuit with an output voltage of 8.7V for a 12V input.
The output voltage is not output properly.

The picture below shows the waveform of the output.
It does not output up to 8.7V. What could be the problem?

  • 0
    TI__Guru 50120 points

    Hi,

    How many boards are showing this issue? Can you also have waveform of VIN, VEN, SW and VCC?

    EN voltage should clear the EN_rising threshold of 1.263V before device begins to switch and regulate output. 

    Looking at the datasheet, the closest output voltage setting for your application would be the 5Vout|2.1MHz design.

    The components you used look similar to the typical external component values. 

    The feedback resistor values look correct for a 8.7V output and output capacitance is appropriate for 2.1MHz design.

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 10 points

    The picture below attaches the waveforms of VIN, VEN, and SW.

  • 0 in reply to BONG HYUN KANG
    TI__Guru 50120 points

    Hi,

    One of the main thing I noticed in the PCB layout is that the SW connection is not connected as recommended in the datasheet. Below is the layout guidelines for connection of CBOOT to SW.

    In your PCB layout, it looks like there is a CBOOT with BOOT connection via through the board back to the boot pin.

    Circled in black is the recommended BOOT-to-SW connection. 

     

    Depending on where the BOOT trace is connected to on the inner layer, it could be coupling noise onto the BOOT node which can impact output regulation. Also VCC capacitor should be right across Pin 2/3 to have as small of a loop as possible for proper operation. It does not look like C561 is on the same layer as the IC. 

    These two points can be contributing to the improper operation of the device. 
    I would suggest taking the existing LMQ61460EVM and configure it for the same application as your system and evaluated to rule out PCB layout.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    Prodigy 10 points

    As you said, the layout was designed differently from the guidelines. We will modify the PCB layout according to the layout guidelines.
    Currently, we have added a capacitor to the VCC pin and confirmed that 8.7v is output. Noise at the VCC pin was also reduced.
    Thanks for your reply.