LM2744 datasheet(2/22 Pages) NSC

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Connection Diagram

20106002

14-Lead Plastic TSSOP

JA = 155˚C/W

NS Package Number MTC14

Pin Description

BOOT (Pin 1) - Bootstrap pin. This is the supply rail for the

high-side gate driver. When the high-side MOSFET turns on,

the voltage on this pin should be at least one gate threshold

above the regulator input voltage V

IN to properly turn on the

MOSFET. See MOSFET Gate Drivers in the Application

Information section for more details on how to select MOS-

FETs.

LG (Pin 2) - Low-gate drive pin. This is the gate drive for the

low-side N-channel MOSFET. This signal is interlocked with

the high-side gate drive HG (Pin 14), so as to avoid shoot-

through.

PGND (Pin 3) - Power ground. This is also the ground for the

low-side MOSFET driver. This pin must be connected on the

PCB ground plane, which is usually also the system ground.

SGND (Pin 4) - Signal ground. It should be connected

appropriately to the ground plane with due regard to good

layout practices in switching power regulator circuits.

CC (Pin 5) Supply rail for the control sections of the IC.

PWGD (Pin 6) - Power Good pin. This is an open drain

output, which is typically meant to be connected to V

CC or

any other low voltage source through a pull-up resistor. The

voltage on this pin is thus pulled low under output fault

conditions (undervoltage or overvoltage) and also under

UVLO.

SEN (Pin 7) - Current limit threshold setting pin. This sources

a fixed 40 µA current. A resistor of appropriate value should

be connected between this pin and the drain of the low-side

MOSFET (switch node).

EAO (Pin 8) - Output of the error amplifier. The voltage level

on this pin is compared with an internally generated ramp

signal to determine the duty cycle. This pin is necessary for

compensating the control loop.

SS/TRACK (Pin 9) - Soft-start and tracking pin. This pin is

internally connected to the non-inverting input of the error

amplifier during soft-start, and in fact any time the SS/

TRACK pin voltage happens to be below the internal refer-

ence voltage. For the basic soft-start function, a capacitor of

minimum value 1nF is connected from this pin to ground. To

track the rising ramp of another power supply’s output, con-

nect a resistor divider from the output of that supply to this

pin as described in Application Information.

FB (Pin 10) - Feedback pin. This is the inverting input of the

error amplifier, which is used for sensing the output voltage

and compensating the control loop.

FREQ (Pin 11) - Frequency adjust pin. The switching fre-

quency is set by connecting a resistor of suitable value

between this pin and ground. The equation for calculating

the exact value is provided in Application Information, but

some typical values (rounded up to the nearest standard

values) are 324 k

Ω for 100 kHz, 97.6 kΩ for 300 kHz, 56.2

Ω for 500 kHz, 24.9 kΩ for 1 MHz.

SD (Pin 12) - IC shutdown pin. Pull this pin to V

CC to ensure

the IC is enabled. Connect to ground to disable the IC. Under

shutdown, both high-side and low-side drives are off. This

pin also features a precision threshold for power supply

sequencing purposes, as well as a low threshold to ensure

minimal quiescent current.

REF (Pin 13) - External reference. This goes to the non-

inverting input of the error amplifier. Any desired reference

voltage between 0.5V to 1.5V can be connected to this pin

(with appropriate filtering if necessary).

HG (Pin 14) - High-gate drive pin. This is the gate drive for

the high-side N-channel MOSFET. This signal is interlocked

with LG (Pin 2) to avoid shoot-through.

LM2744 Datasheet(PDF) 2 Page - National Semiconductor (TI)

LM2744 Datasheet(HTML) 2 Page - National Semiconductor (TI)

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