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New design using PTH04230W

guy lemire
Intellectual 970 points
Other Parts Discussed in Thread: PTH04T230W, PTH04T231W

Hello,

I am looking at a new design. 4.5-5.5V input voltage, Vout=1.8V, current draw will be 3A. I am thinking of using the PTH04230W switcher.

My concern is the output ripple voltage. For a previous desing using a PTH04260W, I had almost 100mVpp of ripple when measured at the output of the regulator (probe over the ceramic capacitior near the output).

In this design, my ripple went from about 50mVpp for light loading (100mA) to about 100mVpp under heavier (approx 1 A) dynamic loading.

I will be adding more ceramic bypass caps closer to the load to reduce the dynamic ripple, but is there an LC filter or some additional capacitance that you can recomment to reduce the baseline switching ripple? I have included two snapshots of the two loads.

regards,

Guy

 

 

  • 0
    TI__Mastermind 38230 points

    Guy:

    I reviewed the data above.. The  scope bandwidth reommended for  ripple and extraneous noise  measurement is not more than 20MHz . The scope in this data is detecting E field noise ( which is not actual present on the  output bus.

    PTH04T230W at 0.0A to 6Amp load is 13mV. The PTH04T230W requires a minimum of 100uF ceramic capacitance plus 150uF non ceramic capacitance.

    PTH04T231W is the all ceramic version .

    Any PI filter on the  out put bus will directly affect  transient  response and possibly the stability of the power module. I recommend  adding additional  47uf or 100uf ceramic capacitors on the output bus. the ceramic capacitor are the best reactive component for ripple attenuation at these frequencies.

    Tom

  • 0 in reply to Tom Guerin
    Intellectual 970 points

    Hi Tom,

    thank you for your reply. But I believe the ripple is present and real and on the bus, and it is most likely due to load transients which are too fast for the switcher and the caps near the switcher to respond to.

    Do you have any simulations with a dynamic switching load (hundreds mA and approx 50-100 Mhz switching frequency)  showing the output ripple at the switcher. I am more concerned about having enough hi frequency capacitance to respond to the load near the load as I understand the switcher has a bandwidth of approx 200kHz and cannot respond at higher frequencies.

    I agree that a PI filter would not do anything to help the ripple and would infact make matters worse.

     

    Regards,

    Guy

  • 0 in reply to guy lemire
    TI__Mastermind 38230 points

    Hi Guy:T

    Thanks for the inforamtion on externally noise.   The  output  noise attenuation  from an external source can be reduced by high frequency ceramic capacitors.  <1uf  and lower multiple of  ceramic capacitors are the only answer to external noise attenuation above 300kHz.

    The ripple amplitude at 300kHz is stated in the product  specifcation

    Can you send me on this reply  your e-mail address:

    Thanks

    Tom