AST1S31HF datasheet(9/33 Pages) STMICROELECTRONICS

9 / 33 page

DocID026968 Rev 2

9/33

AST1S31HF

Functional description

The AST1S31HF device is based on a “peak current mode”, constant frequency control.

The output voltage VOUT is sensed by the feedback pin (FB) compared to an internal

reference (0.8 V) providing an error signal that, compared to the output of the current sense

amplifier, controls the ON and OFF time of the power switch.

The main internal blocks are shown in the block diagram in Figure 3. They are:



A fully integrated oscillator that provides the internal clock and the ramp for the slope

compensation avoiding sub-harmonic instability



The soft-start circuitry to limit the inrush current during the start-up phase



The transconductance error amplifier



The pulse width modulator and the relative logic circuitry necessary to drive the internal

power switches



The drivers for embedded P-channel and N-channel power MOSFET switches



The high-side current sensing block



The low-side current sense to implement diode emulation



The voltage monitor circuitry (UVLO) that checks the input and internal voltages



The thermal shutdown block, to prevent the thermal runaway.

Figure 3. Block diagram

AST1S31HF Datasheet(PDF) 9 Page - STMicroelectronics