NSC LM2737MTCX Datasheet

LM2727/LM2737
N-Channel FET Synchronous Buck Regulator Controller
for Low Output Voltages

General Description

The LM2727 and LM2737 are high-speed, synchronous,
switching regulator controllers. They are intended to control
currents of 0.7A to 20A with up to 95% conversion efficien­cies. The LM2727 employs output over-voltage and under­voltage latch-off. For applications where latch-off is not de­sired, the LM2737 can be used. Power up and down
sequencing is achieved with the power-good flag, adjustable
soft-start and output enable features. The LM2737 and
LM2737 operate from a low-current 5V bias and can convert
from a 2.2V to 16V power rail. Both parts utilize a fixed­frequency, voltage-mode, PWM control architecture and the
switching frequency is adjustable from 50kHz to 2MHz by
adjusting the value of an external resistor. Current limit is
achieved by monitoring the voltage drop across the on­resistance of the low-side MOSFET, which enhances low
duty-cycle operation. The wide range of operating frequen­cies gives the power supply designer the flexibility to fine­tune component size, cost, noise and efficiency. The adap­tive, non-overlapping MOSFET gate-drivers and high-side
bootstrap structure helps to further maximize efficiency. The
high-side power FET drain voltage can be from 2.2V to 16V
and the output voltage is adjustable down to 0.6V.

Features

n Input power from 2.2V to 16V
n Output voltage adjustable down to 0.6V
n Power Good flag, adjustable soft-start and output enable

for easy power sequencing

n Output over-voltage and under-voltage latch-off

(LM2727)

n Output over-voltage and under-voltage flag (LM2737)
n Reference Accuracy: 1.5% (0˚C - 125˚C)
n Current limit without sense resistor
n Soft start
n Switching frequency from 50 kHz to 2 MHz
n TSSOP-14 package

Applications

n Cable Modems
n Set-Top Boxes/ Home Gateways
n DDR Core Power
n High-Efficiency Distributed Power
n Local Regulation of Core Power

Typical Application

20049410

June 2003

LM2727/LM2737 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages

© 2003 National Semiconductor Corporation DS200494 www.national.com

Connection Diagram

20049411

14-Lead Plastic TSSOP

θ

JA

= 155˚C/W

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 to properly turn on the
high-side N-FET.

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

PGND (Pins 3, 13) - Ground for FET drive circuitry. It should
be connected to system ground.

SGND (Pin 4) - Ground for signal level circuitry. It should be
connected to system ground.

V

CC

(Pin 5) - Supply rail for the controller.

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

The pin is pulled low when the chip is in UVP, OVP, or UVLO
mode. During normal operation, this pin is connected to V

CC

or other voltage source through a pull-up resistor.
ISEN (Pin 7) - Current limit threshold setting. This sources a

fixed 50µA 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.

SS (Pin 9) - Soft start pin. A capacitor connected between
this pin and ground sets the speed at which the output
voltage ramps up. Larger capacitor value results in slower
output voltage ramp but also lower inrush current.

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.

FREQ (Pin 11) - The switching frequency is set by connect­ing a resistor between this pin and ground.

SD (Pin 12) - IC Logic Shutdown. When this pin is pulled low
the chip turns off the high side switch and turns on the low
side switch. While this pin is low, the IC will not start up. An
internal 20µA pull-up connects this pin to V

CC

.

HG (Pin 14) - Gate drive for the high-side N-channel MOS­FET. This signal is interlocked with LG to avoid shoot­through problems.

LM2727/LM2737

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Absolute Maximum Ratings (Note 1)

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

V

CC

7V

BOOTV 21V

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 2 kV

Operating Ratings

Supply Voltage (VCC) 4.5V to 5.5V

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

Thermal Resistance (θ

JA

) 155˚C/W

Electrical Characteristics

VCC= 5V 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

V

FB_ADJ

FB Pin Voltage

V

CC

= 4.5V, 0˚C to +125˚C 0.591 0.6 0.609

V

V

CC

= 5V, 0˚C to +125˚C 0.591 0.6 0.609

V

CC

= 5.5V, 0˚C to +125˚C 0.591 0.6 0.609

V

CC

= 4.5V, −40˚C to +125˚C 0.589 0.6 0.609

V

CC

= 5V, −40˚C to +125˚C 0.589 0.6 0.609

V

CC

= 5.5V, −40˚C to +125˚C 0.589 0.6 0.609

V

ON

UVLO Thresholds Rising

Falling

4.2

3.6

V

I

Q-V5

Operating VCCCurrent

SD = 5V, FB = 0.55V
Fsw = 600kHz

1 1.5 2

mA

SD = 5V, FB = 0.65V
Fsw = 600kHz

0.8 1.7 2.2

Shutdown V

CC

Current SD = 0V 0.15 0.4 0.7 mA

t

PWGD1

PWGD Pin Response Time FB Voltage Going Up 6 µs

t

PWGD2

PWGD Pin Response Time FB Voltage Going Down 6 µs

I

SD

SD Pin Internal Pull-up Current 20 µA

I

SS-ON

SS Pin Source Current SS Voltage = 2.5V

0˚C to +125˚C

-40˚C to +125˚C

8
5

11
11

15
15

µA

I

SS-OC

SS Pin Sink Current During Over
Current

SS Voltage = 2.5V

95 µA

I

SEN-TH

I

SEN

Pin Source Current Trip

Point

0˚C to +125˚C

-40˚C to +125˚C

35
28

50
50

65
65

µA

ERROR AMPLIFIER

GBW Error Amplifier Unity Gain

Bandwidth

5 MHz

G Error Amplifier DC Gain 60 dB

SR Error Amplifier Slew Rate 6 V/µA

I

FB

FB Pin Bias Current FB = 0.55V

FB = 0.65V

0
0

15
30

100
155

nA

I

EAO

EAO Pin Current Sourcing and
Sinking

V

EAO

= 2.5, FB = 0.55V

V

EAO

= 2.5, FB = 0.65V

2.8

0.8

mA

V

EA

Error Amplifier Maximum Swing Minimum

Maximum

1.2

3.2

V

LM2727/LM2737

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Electrical Characteristics (Continued)

VCC= 5V 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

GATE DRIVE

I

Q-BOOT

BOOT Pin Quiescent Current BOOTV = 12V, EN = 0

0˚C to +125˚C

-40˚C to +125˚C

95
95

160
215

µA

R

DS1

Top FET Driver Pull-Up ON
resistance

BOOT-SW = 5V

@

350mA 3 Ω

R

DS2

Top FET Driver Pull-Down ON
resistance

BOOT-SW = 5V

@

350mA 2 Ω

R

DS3

Bottom FET Driver Pull-Up ON
resistance

BOOT-SW = 5V

@

350mA 3 Ω

R

DS4

Bottom FET Driver Pull-Down
ON resistance

BOOT-SW = 5V

@

350mA 2 Ω

OSCILLATOR

f

OSC

PWM Frequency

R

FADJ

= 590kΩ 50

kHz

R

FADJ

= 88.7kΩ 300

R

FADJ

= 42.2kΩ, 0˚C to +125˚C 500 600 700

R

FADJ

= 42.2kΩ, -40˚C to +125˚C 490 600 700

R

FADJ

= 17.4kΩ 1400

R

FADJ

= 11.3kΩ 2000

D Max Duty Cycle f

PWM

= 300kHz

f

PWM

= 600kHz

90
88

%

LOGIC INPUTS AND OUTPUTS

V

SD-IH

SD Pin Logic High Trip Point 2.6 3.5 V

V

SD-IL

SD Pin Logic Low Trip Point 0˚C to +125˚C

-40˚C to +125˚C

1.3

1.25

1.6

1.6

V

V

PWGD-TH-LO

PWGD Pin Trip Points FB Voltage Going Down

0˚C to +125˚C

-40˚C to +125˚C

0.413

0.410

0.430

0.430

0.446

0.446

V

V

PWGD-TH-HI

PWGD Pin Trip Points FB Voltage Going Up

0˚C to +125˚C

-40˚C to +125˚C

0.691

0.688

0.710

0.710

0.734

0.734

V

V

PWGD-HYS

PWGD Hysteresis (LM2737 only) FB Voltage Going Down FB Voltage

Going Up

35

110

mV

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

LM2727/LM2737

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Typical Performance Characteristics

Efficiency (VO= 1.5V)

F

SW

= 300kHz, TA= 25˚C

Efficiency (V

O

= 3.3V)

F

SW

= 300kHz, TA= 25˚C

20049412 20049413

VCCOperating Current vs Temperature

F

SW

= 600kHz, No-Load

Bootpin Current vs Temperature for BOOTV = 12V

FSW= 600kHz, Si4826DY FET, No-Load

20049414

20049415

Bootpin Current vs Temperature with 5V Bootstrap

F

SW

= 600kHz, Si4826DY FET, No-Load

PWM Frequency vs Temperature

for R

FADJ

= 43.2kΩ

20049416

20049417

LM2727/LM2737

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Typical Performance Characteristics (Continued)

R

FADJ

vs PWM Frequency

(in 100 to 800kHz range), T

A

= 25˚C

R

FADJ

vs PWM Frequency

(in 900 to 2000kHz range), T

A

= 25˚C

20049418 20049419

VCCOperating Current Plus Boot Current vs

PWM Frequency (Si4826DY FET, T

A

= 25˚C)

Switch Waveforms (HG Falling)

V

IN

= 5V, VO= 1.8V

I

O

= 3A, CSS= 10nF

F

SW

= 600kHz

20049420

20049423

Switch Waveforms (HG Rising)

V

IN

= 5V, VO= 1.8V

I

O

= 3A, FSW= 600kHz

Start-Up (No-Load)

V

IN

= 10V, VO= 1.2V

C

SS

= 10nF, FSW= 300kHz

20049424 20049421

LM2727/LM2737

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Typical Performance Characteristics (Continued)

Start-Up (Full-Load)

V

IN

= 10V, VO= 1.2V

I

O

= 10A, CSS= 10nF

F

SW

= 300kHz

Start Up (No-Load, 10x C

SS

)

V

IN

= 10V, VO= 1.2V

C

SS

= 100nF, FSW= 300kHz

20049422 20049426

Start Up (Full Load, 10x CSS)

V

IN

= 10V, VO= 1.2V

I

O

= 10A, CSS= 100nF

F

SW

= 300kHz

Shutdown

V

IN

= 10V, VO= 1.2V

I

O

= 10A, CSS= 10nF

F

SW

= 300kHz

20049425

20049427

Start Up (Full Load, 10x CSS)

V

IN

= 10V, VO= 1.2V

I

O

= 10A, CSS= 100nF

F

SW

= 300kHz

Load Transient Response (I

O

=0to4A)

V

IN

= 12V, VO= 1.2V

F

SW

= 300kHz

20049433 20049428

LM2727/LM2737

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