Functional description

ST1S31

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DocID022998 Rev 4

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Functional description

The ST1S31 device is based on a “peak current mode”, constant frequency control. The

(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 inrush current during the startup 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



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



A thermal shutdown block, to prevent thermal runaway.

Figure 3. Block diagram

AM11417v1