ST1S32

Functional description

Doc ID 023246 Rev 1

7/29

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Functional description

The ST1S32 is based on a “peak current mode”, constant frequency control. The output

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:

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

compensation avoiding sub-harmonic instability

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

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The transconductance error amplifier

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

power switches

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

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The high-side current sensing block

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The low-side current sense to implement diode emulation

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

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A thermal shutdown block, to prevent thermal run-away.

Figure 3.

Block diagram