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PDF LM2640MTC-ADJ Data sheet ( Hoja de datos )
| Número de pieza | LM2640MTC-ADJ | |
| Descripción | Dual Adjustable Step-Down Switching Power Supply Controller | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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December 1998
LM2640
Dual Adjustable Step-Down Switching Power Supply
Controller
General Description
The LM2640 is a dual step-down power supply controller in-
tended for application in notebook personal computers and
other battery-powered equipment.
Fixed-frequency synchronous drive of logic-level N-channel
power MOSFETs is combined with an optional
pulse-skipping mode to achieve ultra efficient power conver-
sion over a 1000:1 load current range. The pulse-skipping
mode can be disabled in favor of fixed-frequency operation
regardless of the load current level.
High DC gain and current-mode feedback control assure ex-
cellent line and load regulation and a wide loop bandwidth
for fast response to dynamic loads.
An internal oscillator fixes the switching frequency at
200 kHz. Optionally, switching can be synchronized to an ex-
ternal clock running as fast as 400 kHz.
An optional soft-start feature limits current surges from the
input power supply at start up and provides a simple means
of start-up sequencing.
Logic-level inputs allow the controllers to be turned ON and
OFF separately.
Key Specifications
n 96% efficient
n 5.5 to 30V input range
n Dual outputs adjustable from 2.2 to 6V
n 0.5% typical load regulation error
n 0.002%/V typical line regulation error
Features
n 200 kHz fixed-frequency switching
n Switching synchronization with an external signal up to
400 kHz
n Optional pulse-skipping mode
n Adjustable secondary feedback
n Input undervoltage lockout
n Output undervoltage shutdown protection
n Output overvoltage shutdown protection
n Programmable soft-start (each controller)
n 5V, 50 mA linear regulator output
n Precision 2.5V reference output
n 28-pin TSSOP
Applications
n Notebook and subnotebook computers
n Wireless data terminals
n Battery-powered instruments
Connection Diagram and Ordering Information
28-Lead TSSOP (MTC)
DS100148-1
Top View
Order Number LM2640MTC-ADJ
See NS Package Number MTC28
© 1999 National Semiconductor Corporation DS100148
www.national.com
1 page  
Absolute Maximum Ratings (Notes 2, 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
IN, SW1, and SW2
FB1 and FB2
SD, ON/OFF1, ON/OFF2,
2NDFB/FPWM, SYNC, REF,
SS1, SS2, COMP1,
COMP2 and CSL1
LIN
CSH1, CSH2, and CSL2
Voltage from CBOOT1 to SW1
and from CBOOT2 to SW2
Voltage from HDRV1 to SW1
and from HDRV2 to SW2
Voltage from CBOOT1 to
HDRV1 and from CBOOT2
HDRV2
−0.3 to 31V
−0.3 to 3V
−0.3 to (VLIN +0.3)V
−0.3 to 6V
−0.3 to 7V
−0.3 to 5V
−0.3V
−0.3V
Junction Temp.
Power Dissipation (Note 3)
Ambient Storage Temp. (TJ)
Soldering Dwell Time, Temp. (Note 4)
Wave
Infrared
Vapor Phase
ESD Rating (Note 5)
+150˚C
883 mW
−65 to +150˚C
4 sec, 260˚C
10 sec, 240˚C
75 sec, 219˚C
2 kV
Operating Ratings (Notes 1, 2)
VIN
Junction Temp. (TJ)
5.5 to 30V
0 to +125˚C
Electrical Characteristics
Typicals and limits appearing in regular type apply for TJ = 25˚C. Limits appearing in boldface type apply over the entire junc-
tion temperature
= 10V, and VSD
range for operation, 0 to +125˚C. Unless otherwise specified under
= VON/OFF1 = VON/OFF2 = 5V. (Note 2), (Note 6) and (Note 7)
the
Parameter
or
Conditions
columns,
VIN
Symbol
Parameter
Conditions
Typical
Limit
Units
System
VIN Input Supply Voltage Range
5.5 V(min)
30 V(max)
VOUT
Output Voltage Adjustment
Range
2.2 V(min)
6.0 V(max)
∆VOUT/VOUT
Load Regulation
0 mV ≤ (CSH1-CSL1) ≤ 80 mV,
0 mV ≤ (CSH2-CSL2) ≤ 80 mV
0.5
%
∆VOUT/∆VIN
IIN
Line Regulation
Input Supply Current
5.5V ≤ VIN ≤ 30V
ON (Note 8)
VFB1 = VFB2 = 1.4V,
VCSH1 = 5.2V, VCSL1 = 5V,
VCSH2 = 3.5V, VCSL2 = 3.3V
Standing By (Note 9)
0.002
0.6
80
%/V
mA
1 mA(max)
µA
VON/OFF1 = VON/OFF2 = 0V
Shut Down (Note 10)
150 µA(max)
25 µA
ISS1, ISS2
Soft-Start Source Current
VSD = 0V
VSS1 = VSS2 = 1V
60 µA(max)
4.75
µA
2.0 µA(min)
7.0 µA(max)
Soft-Start Sink Current
10 µA
VPCL
VNCL
Positive Current Limit
Voltage (Voltage from CSH1
to CSL1 and from CSH2 to
CSL2)
Negative Current Limit
Voltage (Voltage from CSH1
to CSL1 and from CSH2 to
CSL2)
−40˚C ≤ TJ ≤ +125˚C
V2NDFB/FPWM = 0.8V
100
100
−100
80
140
75
−80
−140
mV
mV(min)
mV(max)
mV(min)
mV
mV(min)
mV(max)
5 www.national.com
5 Page 
Typical Performance Characteristics (Continued)
REF Output Voltage
REF Output Voltage
Normalized Switching
Output Voltage vs
Junction Temperature
DS100148-26
Normalized Error Amplifier
Offset vs Junction Temperature
DS100148-27
Error Amplifier Gm vs
Junction Temperature
DS100148-28
CH1 Skip Frequency
vs Load Current
DS100148-29
Normalized Oscillator Frequency
vs. Junction Temperature
DS100148-30
CH1 Skip Frequency
vs Load Current
DS100148-31
Shutdown Quiescent Current
And Standby Quiescent
Current vs Supply Voltage
DS100148-32
DS100148-33
DS100148-34
Theory of Operation
Basic Operation of the Current-Mode Controller
The output voltage is held at a constant value by the main
control loop, which is made up of the error amplifier, the cur-
rent sense amplifier, and the PWM comparator (refer to the
Block Diagram, Figure 3).
The LM2640 controller has two primary modes of operation:
Forced Pulse-Width Modulation (FPWM) where the control-
ler always operates at a fixed frequency, and Pulse-Skipping
mode where the controller frequency decreases at reduced
output loads to improve light-load efficiency.
FPWM Mode of Operation
Pulling the FPWM pin low initiates a mode of operation
called Forced Pulse-Width Modulation (FPWM). This means
that the LM2640 will always operate at a fixed frequency, re-
gardless of output load. The cycle of operation is:
The high-side FET switch turns ON at the beginning of every
clock cycle, causing current to flow through the inductor. The
11 www.national.com
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