AST1S31HF Datasheet, PDF (9/33 Pages) STMicroelectronics – Internal soft-start and enable

AST1S31HF
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Functional description
Functional description
The AST1S31HF device is based on a “peak current mode”, constant frequency control.
The output voltage V_OUT 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
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