Forum Post: Lm5088 solar MPPT

Helo,

i am trying to build MPPT solar regulator with Lm5088 (input solar panel with Vpp~18V and output is 12V acumulator). I've tested Lm5088 alone, and it worked properly. Next i've modify feedback, with Lm431 reference and AP358 op-amp. When i am changing R4, it regulates input voltage, but it doenst work at desired 220kHz. Input voltage oscillates at frequency 5-10 times lower with Vpp~100mV. Ï thought, thats is a problem of compensation. I've disconnected compensation network and feedback from output voltage and measure signals at FB, COMP, VIN, SW and RAMP. without compensation network i've expected low respective high voltage at COMP pin when FB voltage is higher respective lower then internal 1.205V reference, with fast transients between these two states. But i've measured slow transients like at image 0. Is there some internal compensation ? Or i am missing something ?

Does anybody knows some coockbook to make correct compensation ?

There are schematics and measured signals:



image 0: yellow FB pin, green COMP pin



image 1: SW pin green, FB pin yellow



image 2: RAMP pin green



image 4: Vin (solar panel) green, SW pin yellow





Thanks
Michal