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TPS63710: Reducing output noise od DC-DC converter

Patryk Sikora
Prodigy 10 points
Part Number: TPS63710
Other Parts Discussed in Thread: TPS62912,

Hi,

I need to design ultra low noise power supply for PID controller for our university laser research. Power consumption is estimated around 12V 200 mA for MCU, op amps and ADC/DAC. Output will drive 50 ohm load +-5V.

 

PID controller will be powered by 12V power supply, which I need to convert to symmetric +5V and -5V.

My first idea is to convert input 12V to to 7V by low noise step down converter (TPS62912) and later use linear regultator to achieve low noise 5V.

I want to do the same with negative voltage, so low noise inverting converter and linear regulator.

I want to use  TPS62912 as low noise step down with ferrite bead to reduce voltage ripple. I have few questions about designing of such power supply:

 

1. Is it possible to use TPS63710 with ferrite bead configuration in feedback loop as it is done on TPS62912? I am poosting picture of TPS62912 buck converter.

Could you suggest appropriate schematic with ferrite bead solution since TPS63710 ffedback loop is not externally connected? 

2. According to quesiton 1, will such configuration on TPS63710 be stable?

3. Since I assume my estimated load as low, Do you recommend to additionally dummy load DC-DC converter?

4. Will dummy loading DC-DC converter reduce the noise? I am considering voltage ripples due to low load of the DC-DC converter.

4. Would it be better to dummy load DC-DC converter right after inductor or should I dummy load linear regulator?

5. Could you recommend better DC-DC converter than TPS63710 which also uses spreaded spectrum?

Best regards

Patryk

  • 0
    TI__Expert 4600 points

    Hello, 

    Thanks for the question. Before I answer, do you know which frequency bands your load is sensitive to noise/ripple?  The TPS62912 has the ferrite bead filter to reduce ripple at the FSW and above, while the low noise (100Hz to 100kHz) is achieved through the NRSS cap that is part of the RC filter on the internal voltage reference. The TPS63710 has a similar function with the CAP pin forming the RC filter on the internal reference.

    If you need lower ripple with the TPS63710, it does not have the internal ferrite bead filter compensation that the TPS62912 has, but you can use some other techniques such as external filter compensation and three-terminal filter caps to reduce the ripple. More detail on these methods can be found in the whitepaper here: https://ti.com/lit/slup409. 

  • 0 in reply to Steve Schnier
    Prodigy 10 points

    Hi,

    Thank you for reply.

    My analog circuitry (PID control loop) is designed for DC - 500 kHz band. I find this frequency band most sensitive for control loop. 

    Thank you for attaching an article. I have studied it. I will include ferrite bead and feedthrough capacitor in my design.

    Could you comment my questions about dummy loading DC-DC converter?

    Best regards

    Patryk

  • +1 in reply to Patryk Sikora
    TI__Expert 4600 points

    Hello, 

    The dummy load is useful for devices that have a light load pulse skip operation and discontinuous operation (diode-emulation).  The parts you are looking at are focrced CCM devices without pusle skipping at light loads so a dummy load would not make a difference in the low frequency noise.  

  • 0 in reply to Steve Schnier
    Prodigy 10 points

    Hello,

    Thank you for your comments and support!

    Best regardas

    Patryk