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L7986TA Datasheet(PDF) 8 Page - STMicroelectronics

Part # L7986TA
Description  3 A step-down switching regulator
PDF  43 Pages
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Manufacturer  STMICROELECTRONICS [STMicroelectronics]
Direct Link  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

L7986TA Datasheet(HTML) 8 Page - STMicroelectronics

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Functional description
L7986TA
8/43
Doc ID 022098 Rev 3
5
Functional description
The L7986TA 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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