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LM61460: We are using this as a variable output buck attached to a digital variable resistor MCP45HV51. Please see circuit below

Timothy Darling
Prodigy 20 points
Part Number: LM61460

What this circuit does is that it takes a +/-15V as its input and generates an output from 12V to 30V at currents up to 1/2 Amps. The function of the circuit is to driver a heating element. I will send that photo as well.

The problem is we have a very low noise, precision analog board in the same enclosure and it is getting contaminated from the noise and distortion that is being generated by this switcher. I inherited the design and when the bucks output is loaded we see lots of distortion. Let me see if I can find a photo. Even if I vary the input and output capacitance the noise/distortion is there. There are other DC to DC but the main noise culprit is the LM part.

This is already on the PCB so would like to fix it so that it is less noisy. Thanks and looking forward to dialog. I was a TI FAE for 12 years out of San Diego (MGTS)

  • 0
    TI__Guru 50120 points

    Hi,

    If possible, can you provide a PCB layout for review as well? PCB layout can impact EMI noise.

    Two things that can be done simply from the schematic without looking at PCB layout:

    1. Use of RBOOT (True slew rate control) to adjust the rising edge slew rate of the SW node. You can try a 50Ohm resistor as a starting point and tune accordingly. For more details on this, please refer to Section 10.2.2.7. 
    2. Is there an EMI filter at the input of the converter? If EMI and low noise is an issue, then having an input EMI filter should help significantly mitigate noise. 
    3. Is the inductor that is used a shielded inductor? Can you provide datasheet of L1. Shielded inductors also help with noise mitigation. 

    Regards,

    Jimmy