TPS62050 compensation details

Q: TPS62050 compensation details by 605759

One of our customers, xxxxx, would like details on the internal compensation of the TPS62050, namely the PWM controller ramp voltage, as well as the gain bandwidth product and DC gain of the error amplifier.  I know we generally don't give out much info about the internal compensation of these parts, but is there a MathCAD file or something else I can send to them in order to appease them?  Thanks for your help!

 

Q: Re: TPS62050 compensation details by 10449

Confirmed that the customer has a lot of output capacitance.  As stated earlier in this thread, the larger the output capacitance, the lower the loop gain crossover frequency.  Everything works as expected and this is closed.


Q: Re: TPS62050 compensation details by 10449

Does seem low. Do they have a really big output cap? They asked for the TPS62050 internal compensation info to simulate the loop. Do their sims match their measured data?

Using this part to generate 1V from 3.3V, and measured the crossover frequency to be 17KHz in a sample design, which seems low considering the switching frequency is over 800KHz.  Do you know if this is accurate or what the actual crossover frequency should be?  

: Re: TPS62050 compensation details by 10449

Lower crossover frequency is expected with higher output capacitor values.  I expect the crossover frequency to drop from approximately 50kHz with Cout=10uF down to approximately 20kHz with Cout=100uF.


Q: Re: TPS62050 compensation details by 10449

The TPS62050 uses a non-typical internal compensation scheme.  I can not provide details on how it is implemented.  The result is type 3 compensation.  The power stage has 0db of gain prior to the LC corner frequency.  Internal feedforward keeps this gain at 0db, regardless of input voltage.  The EA internal gain bandwidth is not available.  Its compensation places a zero at 6kHz.  At this point, the gain flattens out to 15dB.  The next zero is at 30kHz.  A final pole is located at 300kHz.  Type 3 compensation typically uses another pole to roll off the internal error amp gain, but the information about this pole is not available.  If you use high quality ceramic output capacitors, the power stage maintains a -40db/decade rolloff, so the overall gain is well controlled and the additional pole is not needed.   The customer can use this to model the loop stability.