National Semiconductor LM2743 Technical data

April 2004

LM2743
N-Channel FET Synchronous Buck Regulator Controller
for Conversion from 3.3V

LM2743 N-Channel FET Synchronous Buck Regulator Controller for Conversion from 3.3V

General Description

The LM2743 is a high-speed, N-Channel synchronous buck
regulator controller with a 2%, 0.6V feedback reference volt­age intended to make down conversion from 3.3V to as low
as 0.6V easy. A fixed-frequency voltage-mode PWM control
architecture is used, that is adjustable from 50kHz to 2MHz
through an external resistor. This wide range of PWM fre­quencies gives the power supply designer the flexibility to
make tradeoffs among component size, cost, noise and
efficiency. The power MOSFETs can run on a separate 1V to
16V (Input Voltage, V
biased from a 3V to 6V (IC Input Voltage, V
power-good flag, precision shutdown threshold and soft start
features make power supply tracking and sequencing easy.
The LM2743 employs output under-voltage and over-voltage
flag, and current limit. Current limit is achieved by monitoring
the voltage drop across the on resistance of the low-side
MOSFET. The adaptive non-overlapping MOSFET gate driv­ers help avoid potential shoot-through problems while main­taining high efficiency. Both high-side and low-side MOS­FETs are the lower cost N-Channel type, and the IC can
accept a bootstrap structure to saturate the high-side MOS­FET for highest efficiency.

) (Note 2) rail while the regulator is

IN

), 2mA rail. A

CC

Typical Application

Features

n MOSFET input voltage (VIN) from 1V to 16V (Note 2)
n IC input voltage (V
n Output voltage adjustable down to 0.6V
n Power good flag and output enable
n Output over-voltage and under-voltage flag
n FB voltage: 2% over temperature
n Current limit without series sense resistor
n Adjustable soft start
n Tracking and sequencing with shutdown and soft start

pins

n Switching frequency from 50 kHz to 2 MHz
n TSSOP-14 package

) from 3V to 6V

CC

Applications

n 3.3V Buck Regulation
n Set-Top Boxes/ Home Gateways
n Core Logic Regulators
n High-Efficiency Buck Regulation

20095201

© 2004 National Semiconductor Corporation DS200952 www.national.com

Connection Diagram

LM2743

14-Lead Plastic TSSOP

θ

JA

NS Package Number MTC14

Pin Description

BOOT (Pin 1) - Supply rail for the N-channel MOSFET gate

drive. The voltage should be at least one gate threshold

) above the regulator input voltage (VIN) to properly

(V

GS(th)

turn on the high-side FET.
LG (Pin 2) - Gate drive for the low-side N-channel MOSFET.

This signal is interlocked with HG (Pin 14) to avoid a shoot­through problem.

PGND (Pins 3, 13) - Ground for low-side FET drive circuitry.
Connect to system ground.

SGND (Pin 4) - Ground for signal level circuitry. Connect to
system ground.

(Pin 5) Supply rail for the controller.

V

CC

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

output. The pin is pulled low when the chip is in under­voltage flag (UVF), over-voltage flag (OVF), or UVLO mode.
During normal operation, this pin is connected to V
other low voltage source through a pull-up resistor (R

).

UP

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

I

SEN

fixed 40µA current. A resistor of appropriate value should be
connected between this pin and the drain of the low-side
FET.

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.

CC

PULL-

= 155˚C/W

or

20095202

SS (Pin 9) - Soft start and track pin. A 10 µA current is
sourced from this pin. This pin is connected to the non­inverting input of the error amplifier during soft start, or any
time the voltage is below the reference. To track power
supplies connect a resistor divider (smaller than 10kΩ for
better precision) from the output of the master supply directly
to the SS pin. To limit the inrush current of a single power
supply, place a capacitor to ground (see Application
Information/Start Up for appropriate capacitance value). This
pin should not be forced before SD or V

(above the

CC

UVLO).
FB (Pin 10) - This is the inverting input of the error amplifier,

which is used for sensing the output voltage and compen­sating the control loop. The FB current is negligible.

FREQ (Pin 11) - The switching frequency (F
connecting a resistor (R

) between this pin and ground.

FADJ

) is set by

OSC

SD (Pin 12) - IC shutdown pin. To assure proper IC start-up
the SD pin should not be left floating. When this pin is pulled
low the chip turns both, high and low, sides off. While this pin
is low, the IC will not start up. This pin features a precision
threshold for power supply sequencing, as well as a lower
threshold to ensure minimal quiescent current.

HG (Pin 14) - Gate drive for the high-side N-channel MOS­FET. This signal is interlocked with LG (Pin 2) to avoid a
shoot-through problem.

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LM2743

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

CC

7V

+ 0.3V

V

CC

BOOT Voltage 21V

All other pins V

Junction Temperature 150˚C

Storage Temperature −65˚C to 150˚C

Soldering Information

Lead Temperature
(soldering, 10sec) 260˚C

Infrared or Convection (20sec) 235˚C

ESD Rating (Note 3) 2 kV

Operating Ratings

IC Input Voltage (VCC) 3Vto6V

Junction Temperature Range −40˚C to +125˚C

Thermal Resistance (θ

) 155˚C/W

JA

Electrical Characteristics

VCC= 3.3V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA=TJ= +25˚C. Limits appearing in
boldface type apply over full Operating Temperature Range. Datasheet min/max specification limits are guaranteed by design,
test, or statistical analysis.

Symbol Parameter Conditions Min Typ Max Units

= 3.3V 0.612 0.6 0.588

V

V

FB

V

ON

FB Pin Voltage

UVLO Thresholds Rising

Operating VCCCurrent

I

Q_VCC

Shutdown VCCCurrent
(Note 4)

t

PWGD1

t

PWGD2

I

SS-ON

I

SS-OC

PWGD Pin Response Time FB Voltage Going Up 6 µs

PWGD Pin Response Time FB Voltage Going Down 6 µs

SS Pin Source Current SS Voltage = 0V 7 10 14 µA

SS Pin Sink Current During Over
Current

I

Pin Source Current Trip

I

SEN-TH

SEN

Point

ERROR AMPLIFIER

GBW Error Amplifier Unity Gain

Bandwidth

G Error Amplifier DC Gain 106 dB

SR Error Amplifier Slew Rate 3.2 V/µs

I

EAO

EAO Pin Current Sourcing and
Sinking Capability

V

EA

Error Amplifier Maximum Swing Minimum

CC

V

=5V 0.612 0.6 0.588

CC

2.76

Falling

V

= 3.3V, SD = 3.3V

CC

Fsw = 600kHz

= 5V, SD = 3.3V

V

CC

Fsw = 600kHz

1 1.5 2.1

1 1.7 2.1

2.42

VCC= 3.3V, SD = 0V 0 110 185 µA

SS Voltage = 0V

90 µA

25 40 55 µA

9 MHz

V

= 1.5, FB = 0.55V

EAO

= 1.5, FB = 0.65V

V

EAO

2.6

9.2

0

Maximum

2

V

V

mA

mA

V

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Electrical Characteristics (Continued)

VCC= 3.3V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA=TJ= +25˚C. Limits appearing in

LM2743

boldface type apply over full Operating Temperature Range. Datasheet min/max specification limits are guaranteed by design,
test, or statistical analysis.

Symbol Parameter Conditions Min Typ Max Units

GATE DRIVE

I

Q-BOOT

R

DS1

R

DS2

R

DS3

R

DS4

OSCILLATOR

F

OSC

D Max Duty Cycle f

LOGIC INPUTS AND OUTPUTS

V

STBY-IH

V

STBY-IL

V

SD-IH

V

SD-IL

V

PWGD-TH-LO

V

PWGD-TH-HI

V

PWGD-HYS

Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device
operates correctly. Opearting Ratings do not imply guaranteed performance limits.

Note 2: The power MOSFETs can run on a separate 1V to 16V rail (Input voltage, V

Note 3: The human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin.

Note 4: Shutdown V

BOOT Pin Quiescent Current BOOTV = 12V, EN = 0 18 90 µA

Top FET Driver Pull-Up ON
resistance

Top FET Driver Pull-Down ON
resistance

Bottom FET Driver Pull-Up ON

BOOT-SW = 5V

@

350mA

resistance

Bottom FET Driver Pull-Down
ON resistance

R

= 813.2kΩ 50

FADJ

= 117.6kΩ 300

R

FADJ

PWM Frequency

R

= 54.4kΩ 475 600 725

FADJ

R

= 18.8kΩ 1400

FADJ

R

= 10.8kΩ 2000

FADJ

= 300kHz

PWM

= 600kHz

f

PWM

Standby High Trip Point FB = 0.575V, BOOTV = 3.3V, EN =

3 Ω

2 Ω

3 Ω

2 Ω

90
85

0.756 1.1 V

0V to 3.3V

Standby Low Trip Point FB = 0.575V, BOOTV = 3.3V, EN =

0.232 0.562

3.3V to 0V

SD Pin Logic High Trip Point FB = 0.575V, BOOTV = 3.3V, EN =

1 1.3

0V to 3.3V

SD Pin Logic Low Trip Point FB = 0.575V, BOOTV = 3.3V, EN =

0.8 1.1

3.3V to 0V

PWGD Pin Trip Points FB Voltage Going Down 0.408 0.434 0.457 V

PWGD Pin Trip Points FB Voltage Going Up 0.677 0.710 0.742 V

PWGD Hysteresis FB Voltage Going Down

FB Voltage Going Up

). Low range of VINgreatly depends on selection of the external MOSFET.

IN

current goes to zero amps after 20 seconds.

CC

60
90

kHz

%

V

V

V

mV

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Typical Performance Characteristics

LM2743

Efficiency (V

= 3.3V, FSW= 300kHz

V

CC

Efficiency (V

= 5V, FSW= 300kHz VCCOperating Current vs Temperature

V

CC

OUT

OUT

= 1.2V)

20095240

= 3.3V)

Efficiency (V

= 3.3V, FSW= 300kHz

V

CC

OUT

= 2.5V)

20095257

20095241

VCCOperating Current plus BOOT Current vs Frequency

FDS689A FET (T

= 25˚C)

A

20095245

20095261

BOOT Pin Current vs Temperature for

BOOT Voltage = 3.3V

FSW= 300kHz, FDS689A FET, No-Load

20095242

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Typical Performance Characteristics (Continued)

LM2743

BOOT Pin Current vs Temperature for

BOOT Voltage = 5V

= 300kHz, FDS689A FET, No-Load

F

SW

20095243

Internal Reference Voltage vs Temperature

BOOT Pin Current vs Temperature for

BOOT Voltage = 12V

FSW= 300kHz, FDS689A FET, No-Load

20095244

R

vs Frequency

FADJ

50kHz to 2MHz, T

= 25˚C

A

20095258

Frequency vs Temperature Output Voltage vs Output Current

20095260

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20095259

20095256

Typical Performance Characteristics (Continued)

LM2743

Switch Waveforms (HG Rising)

V

= 3.3V, VIN= 5V, V

CC

= 4A, CSS= 12nF, FSW= 300kHz

I

OUT

OUT

Start-Up (No-Load)

= 3.3V, VIN= 5V, V

V

CC

= 4A, CSS= 12nF, FSW= 300kHz

I

OUT

OUT

= 1.2V

20095246

= 1.2V

Switch Waveforms (HG Falling)

V

= 3.3V, VIN= 5V, V

CC

= 4A, CSS= 12nF, FSW= 300kHz

I

OUT

OUT

Start-Up (Full-Load)

V

= 3.3V, VIN= 5V, V

CC

= 4A, CSS= 12nF, FSW= 300kHz

I

OUT

OUT

= 1.2V

20095247

= 1.2V

Shutdown (Full-Load)

= 3.3V, VIN= 5V, V

V

CC

= 4A, CSS= 12nF, FSW= 300kHz

I

OUT

OUT

= 1.2V

20095248

20095250

Load Transient Response (I

= 3.3V, VIN= 5V, V

V

CC

= 12nF, FSW= 300kHz

C

SS

=0Ato4A)

OUT

= 1.2V

OUT

20095249

20095251

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