Hi Mr. MC,
I just did the following experiments to check where is the problem.
when I connected just Vin pin of TPS40054 to the solar panel and not the power ciruit IC is working PWM pulses are coming. and Css voltage is 3.7V.
But when I connect power circuit to the solar panel and Vin pin is not connected , then also voltage across Css is reaching 12V and PWM pulses are not coming. I think that there will be some problem with resistor connected between ILIM and drain of upper MOSFET.
Will that resistor effects the voltage across Css ?