AAM resistor Value - MP2313

DC-DC Power Converters
1

I would like to ask some information regarding the AAM resistor value. Performed the measurement for different load (100,300,500)and calculated efficiency for 3 different values of AAM resistor.
Specification in test measurement:

Vin: 13.5V, Vout:3,3V, L-2,2uH.

1.68K
2.40.2K
3.37.4K ( this value is calculated as per the specification input - Figure 7, AAM value -0.225)

Results

  1. 68K efficiency is high and switching frequency not within the specification for light load current.
    Ex:efficiency =86%, fs = 1.0936 load current = 100mA, Vin=13,5V

2.40,2K, efficiency is reduced and switching frequency is within the specification for light load current
Ex.efficieny = 73%,fs = 1.998, load current = 100mA, Vin=13,5V

3.37.4K,efficieny is reduced further and switching frequency is within the specification for light load current
Ex. efficiency= 69%, fs=1.953, load current =100mA, Vin=13,5V

Questions

  1. Which resistor value is recommended to choose from the above results?
  2. which factors is important in terms of choosing the resistor value is it switching frequency or efficiency for light loads?
  3. when the resistor value is calculated as per the specification, efficiency is low? why? based on how the value needs to be calculated.
2

I would like to know the feedback for the above question? When I created the ticket it was mentioned that I will get the reply within 1 business day

3

Hello,

As mentioned in the DS on pg13, there is a trade-off between efficiency / transients and stability / ripple.
Figure 7 is what we have found to be the best trade-off of the two - so we recommend using it to calculate R3.

  1. I would still recommend using the recommended R value calculated from figure 7
  2. Like mentioned earlier, it is a trade-off. You can try to get the highest efficiency at light loads, but then the stability of the converter and ripple will be bad. Given stability and ripple are important, its best to go with the recommended value where efficiency at light load is less.
  3. Operation of AAM is described on page 11. When Vcomp < VAAM, Vcomp ramps up until it exceeds VAAM - during this time the switch is not switching so less losses occur. This is why a larger VAAM means more efficiency and vice versa.

Regards,
Jonathan Hidalgo