The TPS23754 DC-DC controller implements a typical current-mode control as shown in the Functional Block Diagram. Features include oscillator, overcurrent and PWM comparators, current-sense blanker, dead-time control, soft start, and gate driver. In addition, an internal slope-compensation ramp generator, frequency synchronization logic, thermal shutdown, and start-up current source with control are provided.
The TPS23754 is optimized for isolated converters, and does not provide an internal error amplifier. Instead, the optocoupler feedback is directly fed to the CTL pin which serves as a current-demand control for the PWM. There is an offset of VZDC (about 1.5 V) and 2:1 resistor divider between the CTL pin and the PWM. A VCTL below VZDC will stop converter switching, while voltages above (VZDC + (2 × VCSMAX)) will not increase the requested peak current in the switching MOSFET. Optocoupler biasing design is eased by this limited control range.