Hello all,
We have designed a powersupply around the LM5117, I am using it in constant current mode by using the CM pin.
The output current is adjusted by injecting a voltage (PWM signal RC filtered and buffered by op-amp) via a sereis resistor to a voltage divider between the CM pin and FB.
A 3.3V output on the amplifier should give ~0A and 0V is 8A. This works fine.
main components are, 15uH inductor, Rramp = 301K, Cramp = 820pF, 100pf capacitor between CS and CSG and 62R between the current sense resistor and CS pin.
This should give a K factor of about 1. And a gain of ~19 (plus a big tolerance).
I started with a RS of 10mohm but dropped this to 6mohm.
The gain I actually measure is 27 at a 1A load and 23.5 at a 8A load. (at 1A its in DCM mode so that this is not very accurate is excpected)
to get the 6mohm I had placed 3x m50ohm directly on top of the 10mohm (2512).
Except for the gain error this worked fine, and I would except the resistance to be bit higher due to al the solder transistions. (and that this was the cause of the higher gain).
But after removing these and placing a single 6mohm resistor the gain is at 1A 21.5 but when going from DCM to CCM is suddenly jumps to 35.
Any idea what causes this higher gain error? Are my C and R ramp incorrect?
