LM2743MTC National Semiconductor, LM2743MTC Datasheet - Page 9

• Manufacturer Part Number: LM2743MTC
• Description: SYNC SW CONTROL, 3V:6V, POWERWISE
• Manufacturer: National Semiconductor

Specifications of LM2743MTC

• Primary Input Voltage: 16V
• No. Of Outputs: 1
• Output Voltage: 13.5V
• Output Current: 20A
• Voltage Regulator Case Style: TSSOP
• No. Of Pins: 14
• Operating Temperature Range: -40°C To +125°C
• Svhc: No SVHC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Block Diagram
Application Information
THEORY OF OPERATION
The LM2743 is a voltage-mode, high-speed synchronous
buck regulator with a PWM control scheme. It is designed for
use in set-top boxes, thin clients, DSL/Cable modems, and
other applications that require high efficiency buck convert-
ers. It has power good (PWGD) flag, output shutdown (SD),
UVLO mode, and over-voltage flag (OVF) and under- volt-
age flag (UVF) features. The over-voltage and under-voltage
signals are OR gated to drive the power good signal. If this
signal is pulled low, the high side is off and low side if on, but
only if the duty cycle is less then maximum. Current limit is
achieved by sensing the voltage V
FET. During current limit the high side gate is turned off and
the low side gate is turned on. A 90µA source discharges the
soft start capacitor (reducing max. duty cycle) until the cur-
rent is under control.
START UP
When V
a logic high, the internal fixed 10µA source begins charging
the soft start capacitor. During this time the output of the
error amplifier is allowed to rise with the voltage of the soft
start capacitor. This capacitor, C
time, and can be calculated approximately by:
CC
exceeds 2.76V and the shutdown pin (SD) sees
SS
DS
, determines soft start
across the low side
9
During soft start the power good flag is forced low and it is
released when the voltage reaches a set value as shown in
Figure 1. At this point the chip enters normal operation
mode, the power good flag is released, and the OVF and
UVF functions begin to monitor V
OUT
.
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