DC Gain of the System
What you need to stabilize your converter is the control-to-output transfer function: if a stimulus is applied to the duty ratio input, how does it propagate through the converter and create a response on the output. You can obtain this transfer function in various ways, for instance via a small-signal model like the PWM switch model or by using a piece-wise linear simulator like SIMPLIS. The program lets you simulate a switching circuit (and thus observe the cycle-by-cycle waveforms) and delivers the ac response later on after a few seconds.
The below circuit shows a possible example running with Elements, the free demonstration version:

This is a 5-V/100-A full-bridge converter operated in voltage-mode control from a 24-V dc source. The circuit is simplified to let you run it on Elements but a real application would require additional protection circuits like peak current limit for instance. If you run this circuit, you obtain the below transient waveforms confirming the 5-V output:

The control-to-output transfer function is immediate and shows a dc gain of 11.1 dB with the classical second-order response of a buck-derived topology:

If you want to determine the dc gain analytically, it is that of a forward converter:

In this expression, \$V_p\$ represents the peak voltage of the pulse-width modulator (PWM) ramp (2 V in this example), \$V_{in}\$ is the input voltage and \$N\$ represents the transformer turns ratio \$1:N\$.
This dc gain is affected by all the ohmic losses, \$r_{DS(on)}\$, \$r_L\$ etc. which are considered zero here.
You could find many of these converters free templates from my web page. They all run on Elements and will let you explore the transfer functions of these converters.
Now, based on the data-sheet, I would be inclined to think that the peak voltage is around 3.5 V or so because it corresponds to the maximum duty ratio value on one output:

which also corresponds to the clock amplitude if I'm not mistaken.