I am performing a control loop stability test on my 5V DC-DC Buck Converter with the help of this Keysight App Note

I understand that we are injecting a noise signal on the feedback network of this converter and checking how well our converter is responding.

My questions are :

  1. How much noise voltage should we give while testing? What would be the ideal noise voltage that should be injected at the resistor?

  2. I want to understand intuitively where to give the red and black probes from the injection transformer and where to probe Ch1 and Ch2 in the circuit? Where am I injecting the noise (at the top of the 5ohm resistor or at the bottom of the 5ohm resistor) and where am I taking the output?

  3. On Figure 6, is the 0 degree on the phase plot convey actual -180deg ?

It is not clear from the app note

  • \$\begingroup\$ Specify Input and Output voltage ranges. Which regulator or which control used \$\endgroup\$
    – user19579
    Nov 19 '19 at 8:51

The right amplitude of noise depends on the output voltage. The injected noise should be small enough to not disturb the large signal behaviour of the system. That is to say that it does not interfere with the operation point. But on the other hand it should be large enough to be measured/seen. typical values are on the order of 100mV but as said is dependent on the output voltage.

You inject the noise across the 5 ohm you inserted in the "broken" loop. so Black on top op the 5 ohm (vout) and red on the bottom. This is to isolated the injection points. CH1 measures the output while CH2 measures the input relative to ground. In this way you measure the response of the whole system that is power converter and feedback.

  • \$\begingroup\$ When you say "CH1 and CH2" are you referring them with respect to figure 2 or with respect to figure 5 ? \$\endgroup\$
    – Newbie
    Nov 19 '19 at 14:05
  • \$\begingroup\$ figure 2 @Newbie \$\endgroup\$
    – Navaro
    Nov 19 '19 at 14:07

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