The TPS23731 DC-DC controller implements current-mode control as shown in Functional Block Diagram, using internal (via pins FB input and COMP output, with EA_DIS pulled low) or external (via COMP input, with EA_DIS open) voltage control loop error amplifier to define the input reference voltage of the current mode control comparator which determines the switching MOSFET peak current.

V_COMP below V_ZDC causes the converter to stop switching. The maximum (peak) current is requested at approximately (V_ZDC + 5 × (V_CSMAX + V_SLOPE)). The AC gain from COMP to the PWM comparator is typically 0.2.

In flyback applications and with the internal error amplifier enabled, the TPS23731 DC-DC controller can operate with feedback from an auxiliary winding of the flyback power transformer to achieve primary side regulation (PSR), eliminating the need for external shunt regulator and optocoupler. One noteworthy characteristic of this PSR is that it operates with continuous (DC) feedback, enabling better optimization of the power supply, and resulting in significantly lower noise sensitivity.

When combined with secondary-side synchronous rectification (with PSRS open), the opto-less operation of the TPS23731 is achieved with a unique approach which basically consists in actively cancelling (through the use of CP output) the leading-edge voltage overshoot (causing the feedback capacitor to peak-charge) generated by the transformer winding. When combined with a correctly designed power transformer, less than ±1.5% load regulation (typical) over the full output current range becomes achievable in applications making use of secondary-side synchronous rectifiers. Operation is in continuous conduction mode (CCM), also enabling multi-output architectures.

Opto-less operation of the TPS23731 also applies (with PSRS pulled low) to single-output flyback converter applications where a secondary-side diode rectifier is used. In typical 12-V output application and when combined with a correctly designed power transformer, ~±3% load regulation over a wide (< 5% to 100%) output current range can be achieved.

In applications where the internal error amplifier is disabled, the COMP pin receives the control voltage typically from a TL431 or TLV431 shunt regulator driving an optocoupler, using VB pin as a pull up source, although other configurations are possible.