NSC LM3477MMX, LM3477MM, LM3477AMM Datasheet

LM3477/LM3477A High Efficiency High-Side N-Channel Controller for Switching Regulator

General Description

The LM3477/A is a high-side N-channel MOSFET switching regulator controller. It can be used in topologies requiring a high side MOSFET such as buck, inverting (buck-boost) and zeta regulators. The LM3477/A’s internal push pull driver allows compatibility with a wide range of MOSFETs. This, the wide input voltage range, use of discrete power components and adjustable current limit allows the LM3477/A to be optimized for a wide variety of applications.

The LM3477/A uses a high switching frequency of 500kHz to reduce the overall solution size. Current-mode control requires only a single resistor and capacitor for frequency compensation. The current mode architecture also yields superior line and load regulation and cycle-by-cycle current limiting. A 5µA shutdown state can be used for power savings and for power supply sequencing. Other features include internal soft-start and output over voltage protection. The internal soft-start reduces inrush current. Over voltage protection is a safety feature to ensure that the output voltage stays within regulation.

The LM3477A is similar to the LM3477. The primary difference between the two is the point at which the device transitions into hysteretic mode. The hysteretic threshold of the LM3477A is one-third of the LM3477.

Features

n 500kHz switching frequency n Adjustable current limit n 1.5% reference n Thermal shutdown

n Frequency compensation optimized with a single

capacitor and resistor

n Internal softstart n Current mode operation n Undervoltage lockout with hysteresis n 8-lead Mini-SO8 (MSOP-8) package

Applications

n Local Voltage Regulation n Distributed Power n Notebook and Palmtop Computers n Internet Appliances n Printers and Office Automation n Battery operated Devices n Cable Modems n Battery Chargers

Hysteretic Threshold

LM3477 ) 36% of

programmed current limit

LM3477A ) 12% of

programmed current limit

See Hysteretic Threshold and section for more information.

LM3477/LM3477A High Efficiency High-Side N-Channel Controller for Switching Regulator

June 2002

Typical Application Circuit

Typical High Efficiency Step-Down (Buck) Converter

20003333

Connection Diagram

LM3477/LM3477A

8 Lead Mini SO8 Package (MSOP-8 Package)

Package Marking and Ordering Information

Order Number Package Type Package Marking Supplied As:

LM3477MM MSOP-8 S13B 1000 units on Tape and Reel

LM3477MMX MSOP-8 S13B 3500 units on Tape and Reel

LM3477AMM MSOP-8 S13A 1000 units on Tape and Reel

LM3477AMMX MSOP-8 S13A 3500 units on Tape and Reel

Pin Description

Pin Name Pin Number Description

SEN

COMP/SD

FB 3 Feedback pin. The output voltage should be adjusted using a resistor divider to

GND 4 Ground pin.

SW 5 Switch Node. Source of the external MOSFET is connected to this node.

DR 6 Drive pin. The gate of the external MOSFET should be connected to this pin.

CB 7 Boot-strap pin. A capacitor must be connected between this pin and SW pin (pin 5)

1 Current sense input pin. Voltage generated across an external sense resistor is fed

into this pin.

2 Compensation pin. A resistor-capacitor combination connected to this pin provides

compensation for the control loop. Pull this pin below 0.65V to shutdown.

provide 1.270V at this pin.

for proper operation. The voltage developed across this capacitor provides the gate drive for the external MOSFET.

8 Power Supply Input pin.

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LM3477/LM3477A

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/

Lead Temperature for MSOP Package

Vapor Phase (60 sec.) Infared (15 sec.)

Distributors for availability and specifications.

Input Voltage 36V

Peak Driver Output Current (

10µs) 1.0A

CB Pin Voltage (Note 2) 43V

Pin Voltage 500mV

SEN

Power Dissipation Internally Limited

Operating Ratings (Note 1)

Supply Voltage 2.97V ≤ V

Junction Temperature Range −40˚C ≤ T

≤ +125˚C

Storage Temperature Range −65˚C to +150˚C

Junction Temperature +150˚C

ESD Susceptibilty (Note 3)

Human Body Model Machine Model

2kV

200V

Electrical Characteristics (Note 4)

Specifications in Standard type face are for TJ= 25˚C, and in bold type face apply over the full Operating Temperature Range. Unless otherwise specified, V

Symbol Parameter Conditions Typical Limit Units

∆V

LINE

Feedback Voltage V

Feedback Voltage Line Regulation

∆V

UVLO

UV(HYS)

LOAD

Output Voltage Load Regulation

Input Undervoltage Lock-out 2.87

Input Undervoltage Lock-out Hysteresis

DS1 (ON)

Switching Frequency 500

Driver Switch On Resistance (top)

DS2 (ON)

Driver Switch On Resistance (bottom)

CB−VSW)max

max

(on) Minimum On Time 330

min

SUPPLY

Maximum Boot Voltage V

Maximum Duty Cycle 93

Supply Current (switching) (Note 5) 2.0

Quiescent Current in Shutdown Mode

= 12V.

= 1.4V,

COMP

2.97V ≤ V

≤ 36V

1.270

1.260/1.252

1.288/1.290

V(min)

V(max)

2.97V ≤ VIN≤ 36V 0.001 %/V

0.5 %/V (max)

2.97

V(max)

180

130 225

435 575

mV (min)

mV (max)

kHz(min)

kHz(max)

IDR= 0.2A, VIN=5V 7 Ω

IDR= 0.2A 4 Ω

7.2V V

≥ 7.2V 7.2

230 495

3.0

%(min)

nsec(min)

nsec(max)

mA (max)

(Note 6), VIN=5V 5

µA (max)

215˚C 220˚C

≤ 35V

kHz

nsec

µA

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Electrical Characteristics (Note 4) (Continued)

Specifications in Standard type face are for TJ= 25˚C, and in bold type face apply over the full Operating Temperature Range. Unless otherwise specified, V

Symbol Parameter Conditions Typical Limit Units

CL(O)

LM3477/LM3477A

CL(100)

Current Limit Voltage at 0% Duty Cycle

Current Limit Voltage at 100% Duty Cycle

Short-Circuit Current Limit Sense Voltage

Internal Compensation Ramp Voltage Height

OVP

Output Over-voltage Protection (with respect to feedback voltage) (Note 7)

OVP(HYS)

Output Over-Voltage Protection Hysteresis(Note 7)

Gm Error Amplifier

Transconductance

VOL

EAO

Error Amplifier Voltage Gain V

Error Amplifier Output Current (Source/ Sink)

EAO

Error Amplifier Output Voltage Swing

Internal Soft-Start Delay VFB= 1.2V, V

Drive Pin Rise Time CGS= 3000pF, VDR=0

Drive Pin Fall Time CGS= 3000pF, VDR=0

= 12V.

LM3477 155

130/125 185/190

LM3477A 165

140/135 195/200

LM3477 74

50/43 98/98

LM3477A 65

41/25 89/98

VIN= 5V, LM3477 350

270 420

= 5V, LM3477A 310

260 380

VIN= 5V, LM3477 83 mV

= 5V, LM3477A 103

= 1.4V 50

COMP

32/25 78/85

= 1.4V 60

COMP

110

= 1.4V

COMP

= 100µA

EAO

(Source/Sink)

= 1.4V

COMP

= 100µA

EAO

(Source/Sink)

Source, V V

COMP

=0V

= 1.4V,

750

600/365

1000/1265

30 42

100

75/50

130/160

Sink, V

= 1.4V

COMP

= 1.4V, V

−140

−110/−95

−170/−180

Upper Limit

=0V

COMP Pin = Floating

Lower Limit

= 1.4V

2.2

2.0

2.35

0.75

0.5

0.95

COMP

5 msec

Floating

25 ns

to 3V

25 ns

to 3V

mV (min)

mV (max)

mV (min)

mV (max)

mV (min)

mV (max)

mV (min)

mV (max)

mV (min)

mV (max)

mV (min)

mV (max)

mV(min)

mV(max)

mV(min)

mV(max)

µmho

µmho (min)

µmho (max)

V/V

V/V (min)

V/V (max)

µA

µA (min)

µA (max)

µA

µA (min)

µA (max)

V(min)

V(max)

V(min)

V(max)

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Electrical Characteristics (Note 4) (Continued)

Specifications in Standard type face are for TJ= 25˚C, and in bold type face apply over the full Operating Temperature Range. Unless otherwise specified, V

Symbol Parameter Conditions Typical Limit Units

Shutdown Threshold (Note 8) Output = High 1.15

Shutdown Pin Current VSD=5V −1

TSD Thermal Shutdown 165 ˚C

Thermal Shutdown Hysteresis 10 ˚C

Thermal Resistance MM Package 200 ˚C/W

= 12V.

Output = Low 0.65

=0V +1

1.35

0.3

V (max)

V (min)

µA

LM3477/LM3477A

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Electrical Characteristics (Note 4) (Continued)

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device

is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: The CB pin must not be higher than 8V above the V

Note 3: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is 200 pF capacitor discharged directly

into each pin.

Note 4: All limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%

LM3477/LM3477A

tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

Note 5: For this test, the COMP/SD pin must be left floating.

Note 6: For this test, the COMP/SD pin must be pulled low.

Note 7: The over-voltage protection is specified with respect to the feedback voltage. This is because the over-voltage protection tracks the feedback voltage. The

overvoltage protection threshold is given by adding the feedback voltage, V

Note 8: The COMP/SD pin should be pulled to ground to turn the regulator off. The voltage on the COMP/SD pin must be below the limit for Output = Low to keep the regulator off.

to the over-voltage protection specification.

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LM3477/LM3477A

Typical Performance Characteristics Unless otherwise specified, V

(Shutdown) vs Temperature & Supply Voltage I

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vs Temperature & Supply Voltage (Switching) Frequency vs Temperature

Supply

vs Temperature & Supply Voltage (Non-Switching)

Supply

= 12V, TJ= 25˚C.

20003315 20003316

VCB−VSWvs Supply Voltage COMP Pin Voltage vs Load Current

20003362

20003320

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