ADRV9001 Power Stage Design Details

Question

Hello, 
 I am wondering if there are more details on the power stage design for the ADRV9001/EVAL-ADRV9002 than already present in the ADRV9001 System Development User Guide , or some reference simulations one can obtain. 
 Specifically, my question is related to the feedforward capacitor from VOUTx to the FBx pin on the ADP5056, used to "improve transient performance" according to the ADP5056 Datasheet . I notice in other reference designs for the ADP5056, this capacitor is 180 pF. However, slightly more involved filters employing 10 nF capacitors and some resistors are used on the ADRV9001. Would it be possible to gain more insight as to why this was done? 
 
 Thank you in advance, 
 T. Stana

John_M · Accepted Answer

HI 
 On the ADP5056 the larger cap will yield a slower transient response. it&rsquo;s to compensate the secondary output LC filter. If you don&rsquo;t have that filter, you can simply use C without the series R. 
 In the EVAL-ADRV9002 board the the larger capacitor has a longer transient response and is the fast portion of the FB circuitry. There is a second control loop (slower) with a resistor connected down stream after the current sense resistor that it is using to control the FB. 
 There are no available simulation models but you could use LT Spice to simulator the filter alone and with the ADP5056. 
 
 John)