L7986 STMicroelectronics, L7986 Datasheet - Page 8

• Manufacturer Part Number: L7986
• Description: 3A step-down switching regulator
• Manufacturer: STMicroelectronics

Specifications of L7986

• Low Dropout Operation: 100% duty cycle

Functional description
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Functional description
The L7986 is based on a “voltage mode”, constant frequency control. The output voltage
V
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.
OUT
COMP
COMP
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. To supply the internal circuitry and provide a
fixed internal reference.
A voltage monitor circuitry (UVLO) that checks the input and internal voltages.
A thermal shutdown block, to prevent thermal runaway.
EN
EN
is sensed by the feedback pin (FB) compared to an internal reference (0.6 V) providing
Block diagram
0.6V
0.6V
TRIMMING
TRIMMING
START
START
SOFT-
SOFT-
EN
EN
FB
FB
1.254V
1.254V
E/A
E/A
Doc ID 022450 Rev 1
FSW
FSW
SHUTDOWN
SHUTDOWN
REGULATOR
REGULATOR
REGULATOR
THERMAL
THERMAL
BANDGAP
BANDGAP
BANDGAP
OSCILLATOR
OSCILLATOR
3.3V
3.3V
&
&
&
GND
GND
PWM
PWM
CURRENT
CURRENT
PHASE SHIFT
PHASE SHIFT
UVLO
UVLO
UVLO
PEAK
PEAK
LIMIT
LIMIT
S
S
R
R
SYNCH
SYNCH
&
&
SYNCH
SYNCH
Figure
Q
Q
DRIVER
DRIVER
3. They are:
VCC
VCC
OUT
OUT
L7986