National Semiconductor LM2727, LM2737 Technical data

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

June 2003

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.

Typical Application

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

20049410

Connection Diagram

LM2727/LM2737

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 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.

(Pin 5) - Supply rail for the controller.

V

CC

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 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.

CC

20049411

= 155˚C/W

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

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

.

CC

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LM2727/LM2737

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

Infrared or Convection (20sec) 235˚C

ESD Rating 2 kV

please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Operating Ratings

V

CC

BOOTV 21V

Junction Temperature 150˚C

Storage Temperature −65˚C to 150˚C

Soldering Information

Lead Temperature (soldering, 10sec) 260˚C

7V

Supply Voltage (VCC) 4.5V to 5.5V

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

Thermal Resistance (θ

) 155˚C/W

JA

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

= 4.5V, 0˚C to +125˚C 0.591 0.6 0.609

CC

= 5V, 0˚C to +125˚C 0.591 0.6 0.609

V

CC

V

= 5.5V, 0˚C to +125˚C 0.591 0.6 0.609

V

FB_ADJ

V

I

t

PWGD1

t

PWGD2

I

SS-ON

I

SS-OC

ON

Q-V5

I

SD

FB Pin Voltage

UVLO Thresholds Rising

Operating VCCCurrent

Shutdown V

Current SD = 0V 0.15 0.4 0.7 mA

CC

PWGD Pin Response Time FB Voltage Going Up 6 µs

PWGD Pin Response Time FB Voltage Going Down 6 µs

SD Pin Internal Pull-up Current 20 µA

SS Pin Source Current SS Voltage = 2.5V

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 60 dB

SR Error Amplifier Slew Rate 6 V/µA

I

FB

EAO

FB Pin Bias Current FB = 0.55V

EAO Pin Current Sourcing and Sinking

V

EA

Error Amplifier Maximum Swing Minimum

CC

V

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

CC

V

= 5V, −40˚C to +125˚C 0.589 0.6 0.609

CC

V

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

CC

4.2

Falling

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

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

0˚C to +125˚C

-40˚C to +125˚C

SS Voltage = 2.5V

0˚C to +125˚C

-40˚C to +125˚C

1 1.5 2

0.8 1.7 2.2

8 5

35 28

3.6

11 11

95 µA

50 50

5 MHz

FB = 0.65V

V

= 2.5, FB = 0.55V

EAO

= 2.5, FB = 0.65V

V

EAO

0 0

15 30

2.8

0.8

1.2

Maximum

3.2

15 15

65 65

100 155

V

mA

µA

nA

mA

V

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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

LM2727/LM2737

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

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

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

Top FET Driver Pull-Up ON resistance

Top FET Driver Pull-Down ON resistance

Bottom FET Driver Pull-Up ON resistance

Bottom FET Driver Pull-Down ON resistance

PWM Frequency

0˚C to +125˚C

-40˚C to +125˚C

@

BOOT-SW = 5V

R

= 590kΩ 50

FADJ

= 88.7kΩ 300

R

FADJ

R

= 42.2kΩ, 0˚C to +125˚C 500 600 700

FADJ

R

= 42.2kΩ, -40˚C to +125˚C 490 600 700

FADJ

R

= 17.4kΩ 1400

FADJ

R

= 11.3kΩ 2000

FADJ

= 300kHz

PWM

= 600kHz

f

PWM

350mA 3 Ω

@

350mA 2 Ω

@

350mA 3 Ω

@

350mA 2 Ω

95 95

90 88

SD Pin Logic High Trip Point 2.6 3.5 V

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

-40˚C to +125˚C

1.3

1.25

1.6

PWGD Pin Trip Points FB Voltage Going Down

0˚C to +125˚C

-40˚C to +125˚C

0.413

0.410

0.430

0.446

PWGD Pin Trip Points FB Voltage Going Up

0˚C to +125˚C

-40˚C to +125˚C

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

Going Up

0.691

0.688

0.710

35

110

0.734

160 215

µA

kHz

%

V

mV

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Typical Performance Characteristics

LM2727/LM2737

Efficiency (VO= 1.5V)

= 300kHz, TA= 25˚C

F

SW

20049412 20049413

VCCOperating Current vs Temperature

= 600kHz, No-Load

F

SW

Efficiency (V

= 300kHz, TA= 25˚C

F

SW

= 3.3V)

O

Bootpin Current vs Temperature for BOOTV = 12V

FSW= 600kHz, Si4826DY FET, No-Load

20049414

Bootpin Current vs Temperature with 5V Bootstrap

= 600kHz, Si4826DY FET, No-Load

F

SW

20049416

PWM Frequency vs Temperature

for R

FADJ

= 43.2kΩ

20049415

20049417

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Typical Performance Characteristics (Continued)

(in 100 to 800kHz range), T

LM2727/LM2737

VCCOperating Current Plus Boot Current vs

PWM Frequency (Si4826DY FET, T

R

vs PWM Frequency

FADJ

= 25˚C

A

R

vs PWM Frequency

FADJ

(in 900 to 2000kHz range), T

20049418 20049419

A

Switch Waveforms (HG Falling)

V

= 5V, VO= 1.8V

IN

= 3A, CSS= 10nF

I

= 25˚C)

A

O

F

SW

= 600kHz

= 25˚C

20049420

Switch Waveforms (HG Rising)

= 5V, VO= 1.8V

V

IN

= 3A, FSW= 600kHz

I

O

20049424 20049421

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Start-Up (No-Load)

V

= 10V, VO= 1.2V

IN

= 10nF, FSW= 300kHz

C

SS

20049423

Typical Performance Characteristics (Continued)

Start-Up (Full-Load)

V

= 10V, VO= 1.2V

IN

= 10A, CSS= 10nF

I

O

Start Up (Full Load, 10x CSS)

V

I

O

= 300kHz

F

SW

= 10V, VO= 1.2V

IN

= 10A, CSS= 100nF

= 300kHz

F

SW

20049422 20049426

Start Up (No-Load, 10x C

= 10V, VO= 1.2V

V

IN

= 100nF, FSW= 300kHz

C

SS

Shutdown

V

= 10V, VO= 1.2V

IN

= 10A, CSS= 10nF

I

O

F

SW

= 300kHz

LM2727/LM2737

)

SS

Start Up (Full Load, 10x CSS)

= 10V, VO= 1.2V

V

IN

= 10A, CSS= 100nF

I

O

F

SW

= 300kHz

20049425

Load Transient Response (I

= 12V, VO= 1.2V

V

IN

= 300kHz

F

SW

20049433 20049428

=0to4A)

O

20049427

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