NSC LM2631MTCX-ADJ, LM2631MTC-ADJ Datasheet

LM2631
Synchronous Step-Down Power Supply Controller

General Description

The LM2631 controller provides all the active functions for
step-down (buck)switching converters. These dc-to-dc con­verters provide core CPU power in battery-operated sys­tems.

High efficiency is achieved by using synchronous rectifica­tion and pulse-skipping mode operation at light load. Inex­pensive N-channel MOSFETs are used to reduce system
cost. Bootstrap circuit is used to drive the high-side
N-channel MOSFET.

Current mode control schemeis used to improve line regula­tion and transient response, also provides cycle-by-cycle
current limiting.

The operating frequency is adjustable between 200 kHz and
400 kHz. An external shutdown pin can be used to disable
the device and reducethe quiescent current to 0.1µA. In low
noise applications, bringing theFPWMpin high can force the
device to operate in constant frequency mode. Other fea­tures include the external synchronization pin, and the
PGOOD pin to indicate the state of the output voltage.

Protection circuitry includesthermal shutdown, undervoltage
and overvoltage shutdown protection, soft-start capability,
and two levels of current limits: The first level simply limits
the load current directly; at the second level, if the load pulls
the output voltage down below 80%of the regulated value,
the chip will shut down. This operation is disabled during
startup, but an internal timer will enable it if the output does
not come up in the preset time.

Features

n 4.5V to 30V input range
n Adjustable output (1.5V to 7V)
n 200 kHz to 400 kHz adjustable operating frequency
n Externally synchronizable
n On-board power good function
n Precision 1.24V reference output
n 0.8 mA typical quiescent current
n 0.1 µA shutdown current
n Thermal shutdown
n Direct current limit protection
n Input undervoltage lockout
n Output undervoltage shutdown protection
n Output overvoltage shutdown protection
n Programmable soft-start function
n Tiny TSSOP package

Applications

n Notebook and subnotebook computers
n Cellular phones
n Portable instruments
n Battery-powered digital devices

Typical Application Circuit

DS100937-1

April 1999

LM2631 Synchronous Step-Down Power Supply Controller

© 1999 National Semiconductor Corporation DS100937 www.national.com

Absolute Maximum Ratings (Note 1)

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

Voltages from the indicated
pins to GND and PGND:

V

IN

−0.3V to 32V
CBOOT −0.3V to 37V
SD

−0.3V to 32V
SW −0.3V to 32V
CSH, CSL −0.3V to 8V
FPWM, SYNC −0.3V to 10V
Power Dissipation (T

A

=

70˚C), (Note 2)

720mW

Storage Temperature Range −65˚C to +150˚C
Soldering Dwell Time,

Temperature (Note 3)

Wave 4 sec, 260˚C
Infrared 10 sec, 240˚C
Vapor Phase 75 sec, 219˚C

ESD Rating (Note 4) 1.5 kV

Operating Ratings

V

IN

4.5V to 30V

Junction Temperature −25˚C to +125˚C

Electrical Characteristics

Specifications in standard type face are for T

j

=

25˚C and those with boldface type apply over full operating junction tem-

perature range. V

IN

=

10V, GND=PGND=0V,unless otherwise stated. (Notes 5, 6)

Symbol Parameter Conditions Typical Limit Units

System

V

IN

Input Supply Voltage 4.5

30

V(min)

V(max)

V

OUT

Output Voltage Adjustment Range 1.5

7.0

V(min)

V(max)

∆V

OUT

/

V

OUT

Load Regulation 0 mV ≤ (CSH-CSL) ≤ 75 mV

0.3

%

∆V

OUT

/

V

OUT

Line Regulation 4.5 ≤ VIN≤ 30V

0.002

%

/V

I

IN

Input Supply Current with the
Switching Controller ON

V

FB

=

1V, V

CSH

=

2.15V, V

CSL

=

2.1V

0.8 mA

1.2/1.4 mA(max)

Input Supply Current with the
Switching Controller ON (Internal
Rail is Supplied from CSL Pin)

V

FB

=

1V, V

CSH

=

5.15V, V

CSL

=

5V 0.15 mA

Input Supply Current with the IC
Shut Down

V

SD

=

0V, V

IN

=

30V

0.1 µA
3 (Note 7) µA(max)

Minimum Output Voltage for CSL
Providing the Internal Rail

3V

I

SS

Soft Start Source Current V

SS

=

1.5V 10 µA

5 µA(min)

13 µA(max)

Soft Start Sink Current V

SS

=

1.5V 20 µA

V

CL

Current Limit Voltage (Voltage
from CSH to CSL)

V

FB

=

1V, V

CSL

=

1.8V 110 mV
90/80 mV(min)

130/140 mV(max)

V

IN

Undervoltage Shutdown Latch

Threshold

Rising Edge 3.5 V

2.6 V(min)

V

OUT

Undervoltage Shutdown

Latch Threshold (Note 8)

80

%

V

OUT

72/70

%

V

OUT

(min)

89/90

%

V

OUT

(max)

V

OUT

Overvoltage Shutdown

Latch Threshold (Note 8)

120

%

V

OUT

113/110

%

V

OUT

(min)

129/130

%

V

OUT

(max)

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Electrical Characteristics (Continued)

Specifications in standard type face are for T

j

=

25˚C and those with boldface type apply over full operating junction tem-

perature range. V

IN

=

10V, GND=PGND=0V,unless otherwise stated. (Notes 5, 6)

Symbol Parameter Conditions Typical Limit Units

System

V

OUT

Low Regulation Comparator

Enable Threshold

97

%

V

OUT

Hysteresis of Low Regulation
Comparator

2

%

V

OUT

Regulator Window Detector
Thresholds (PGOOD from High to
Low)

91 or 109

%

V

OUT

Regulator Window Detector
Thresholds (PGOOD from Low to
High)

97 or 103

%

V

OUT

Gate Drive

V

BOOT

Bootstrap Voltage (Voltage from
CBOOT to SW)

CBOOT Sourcing 100 µA 4.5 V

4.0 V(min)

I

BOOT

CBOOT Leakage Current V

CBOOT

=

7V 100 nA

High Drive Source Current V

HDRV

=

0V, V

CBOOT

=

5V 0.3 A
High Drive Sink Current HDRV Forced to 5V 0.45 A
Low Drive Source Current LDRV Forced to 0V 0.35 A
Low Drive Sink Current LDRV Forced to 5V 0.55 A
High-Side FET On-Resistance

HDRV or LDRV

8 Ω

Low-Side FET On-Resistance
HDRV or LDRV

4 Ω

Oscillator

F

OSC

Oscillator Frequency FADJ Open 200 kHz

172/162 kHz(min)
228/230 kHz(max)

Oscillator Frequency FADJ Sourcing 2.94 µA (Note 9) 300 kHz

255 kHz(min)
345 kHz(max)

V

FADJ

Voltage at FADJ pin 1.03 V

D

MAX

Maximum Duty Cycle FADJ Open 96

%

92

%

(min)

Maximum Frequency of
Synchronization

Low-Going 200 ns Wide
Rectangular Pulses Applied at
400 kHz at the SYNC Input

400 kHz(min)

Minimum Pulse Width of the
SYNC Signal

SYNC Pulses are Low-Going

200 ns(min)

Error Amplifier

I

FB

Feedback Input Bias Current V

FB

=

1.3V, V

CSH

=

5.15V, V

CSL

=

5V

100 nA

I

COMP

COMP Output Source Current V

COMP

=

0.2V, V

FB

=

1V 50 µA

COMP Output Sink Current V

COMP

=

1.2V, V

FB

=

1.4V 50 µA

Voltage Reference

V

REF

Reference Voltage (Nominal)) I

REF

=

0µA 1.238 V

1.219/1.219 V(min)

1.251/1.262 V(max)

www.national.com3

Electrical Characteristics (Continued)

Specifications in standard type face are for T

j

=

25˚C and those with boldface type apply over full operating junction tem-

perature range. V

IN

=

10V, GND=PGND=0V,unless otherwise stated. (Notes 5, 6)

Symbol Parameter Conditions Typical Limit Units

Voltage Reference

V

REF

Reference Voltage (Line
Regulation)

4.5V<V

IN

<

30V 1.238 V

1.219/1.219 V(min)

1.251/1.262 V(max)

Reference Voltage (Load
Regulation)

0µA

<

I

REF

<

50 µA 1.238 V

1.219/1.219 V(min)

1.251/1.262 V(max)

Logic Inputs and Outputs

V

IH

Minimum High Level Input
Voltage (SD, FPWM and SYNC)

2.4 V(min)

V

IL

Maximum Low Level Input
Voltage (FPWM and SYNC)

0.8 V(max)

Maximum Low Level Input
Voltage (SD)

0.5

V(max)

Maximum Input Leakage Curren1t
(SD , FPWM and SYNC)

Logic Input Voltage 0V or 5V

±

0.1 µA

V

OH

PGOOD High Level Output
Voltage

PGOOD Sourcing 50 µA 2.7 V

2.4 V(min)

V

OL

PGOOD Low Level Output
Voltage

PGOOD Sinking 50 µA 0 V

0.5 V(max)

Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device

outside of its rated operating conditions.
Note 2: The maximum allowable power dissipation is calculated by using P

Dmax

=

(T

Jmax-TA

)/θJA, where T

Jmax

is the maximum junction temperature, TAis the

ambient temperature, and θ

JA

is the junction-to-ambient thermal resistance of the specified package. The 720 mW rating results from using 160˚C, 70˚C, and

125˚C/W for T

Jmax,TA

, and θJArespectively.AθJAof 125˚C/W represents the worst-casecondition of no heat sinking of the 20-pinTSSOP. Heat sinking allows the
safe dissipation ofmorepower. The AbsoluteMaximumpowerdissipationmust be derated by 8 mW per ˚C above 70˚C ambient. The LM263 actively limits its junction
temperature to about 160˚C.

Note 3: For detailed information on solderingplastic small-outlinepackages, refer to the PackagingDatabook available from National Semiconductor Corporation.
Note 4: For testing purposes, ESD was applied using the human-body model, a 100 pF capacitor discharged through a 1.5 kΩ resistor.
Note 5: A typical is the center of characterization data taken with T

A

=

T

J

=

25˚C. Typicals are not guaranteed.

Note 6: All limits are guaranteed. All electrical characteristics having room-temperature limits are tested during production with T

A

=

T

J

=

25˚C.All hot and cold limits

are guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control.

Note 7: This limit is guaranteed by design.
Note 8: Percentage limits are determined by measuring the shutdown latch threshold at the FB pin, and dividing it by the nominal reference voltage.
Note 9: Pulling 2.94 µA out of FADJ pin simulates adjusting the oscillator frequency with a 350 kΩ resistor connected from FADJ to GND.

Typical Performance Characteristics

Efficiency vs Load Current
(FPWM=Low, V

OUT

=

3.3V)

DS100937-11

Efficiency (FPWM=High, Input Voltage=16V
V

OUT

=

2.9V)

DS100937-12

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