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L7981ATR 데이터시트(PDF) 8 Page - STMicroelectronics

부품명 L7981ATR
상세설명  3 A step-down switching regulator
PDF  44 Pages
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제조업체  STMICROELECTRONICS [STMicroelectronics]
홈페이지  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

L7981ATR 데이터시트(HTML) 8 Page - STMicroelectronics

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Functional description
L7981
8/44
Doc ID 15182 Rev 3
5
Functional description
The L7981 is based on a “voltage mode”, constant frequency control. The output voltage
VOUT is sensed by the feedback pin (FB) compared to an internal reference (0.6 V) providing
an error signal that, compared to a fixed frequency sawtooth, 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 sawtooth to modulate the duty cycle and the
synchronization signal. Its switching frequency can be adjusted by an external resistor.
The voltage and frequency feed forward are implemented.
●
The soft-start circuitry to limit inrush current during the start up phase.
●
The voltage mode error amplifier
●
The pulse width modulator and the relative logic circuitry necessary to drive the internal
power switch.
●
The high-side driver for embedded p-channel power MOSFET switch.
●
The peak current limit sensing block, to handle over load and short circuit conditions.
●
A voltage regulator and internal reference. It supplies internal circuitry and provides a
fixed internal reference.
●
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
PEAK
CURRENT
LIMIT
OSCILLATOR
S
R
Q
THERMAL
SHUTDOWN
SOFT-
START
EN
TRIMMING
UVLO
0.6V
REGULATOR
&
BANDGAP
1.254V
3.3V
SYNCH
&
PHASE SHIFT
EN
FB
COMP
FSW
GND
SYNCH
OUT
VCC
DRIVER
E/A
PWM
PEAK
CURRENT
LIMIT
OSCILLATOR
S
R
Q
THERMAL
SHUTDOWN
SOFT-
START
EN
TRIMMING
UVLO
UVLO
0.6V
REGULATOR
&
BANDGAP
REGULATOR
&
BANDGAP
1.254V
3.3V
SYNCH
&
PHASE SHIFT
EN
FB
COMP
FSW
GND
SYNCH
OUT
VCC
DRIVER
E/A
PWM



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