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R7986ATR Folha de dados(PDF) 8 Page - STMicroelectronics

Nome de Peças R7986ATR
Descrição Electrónicos  3 A step-down switching regulator for aerospace applications
PDF  37 Pages
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Fabricante Electrônico  STMICROELECTRONICS [STMicroelectronics]
Página de início  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

R7986ATR Folha de dados(HTML) 8 Page - STMicroelectronics

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Functional description
R7986A
8/37
DocID026997 Rev 1
5
Functional description
The R7986A device 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 2. 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 startup 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 overload 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 runaway.
Figure 2. 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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