ST1S40 Datasheet, PDF (7/29 Pages) STMicroelectronics – 3 A DC step-down switching regulator

ST1S40
5
Functional description
Functional description
The ST1S40 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 inrush current during the startup phase
 The transconductance error amplifier with integrated compensation network
 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 run-away.
Figure 3. Block diagram
OSC
OCP
REF
COMP
Vsum
Vc
COMP
OCP
VINA
REGULATOR
UVLO
MOSFET
CONTROL
LOGIC
I2V
I_SENSE
Vdrv_p _DRIVER
Vdrv_n
OTP
E/A
DMD
VINSW
R_SENSE
SW
SOFTSTART
0.8V
SHUT-DOWN
FB
EN
DRIVER
GNDA
GNDP
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