LM2704
Micropower Step-up DC/DC Converter with 550mA Peak
Current Limit
General Description
The LM2704 is a micropower step-up DC/DC in a small
5-lead SOT-23 package. A current limited, fixed off-time
control scheme conserves operating current resulting in high
efficiency over a wide range of load conditions. The 21V
switch allows for output voltages as high as 20V. The low
400ns off-time permits the use of tiny, low profile inductors
and capacitors to minimize footprint and cost in space-
conscious portable applications. The LM2704 is ideal for
LCD panels requiring low current and high efficiency as well
as white LED applications for cellular phone back-lighting.
The LM2704 can drive up to 8 white LEDs from a single
Li-Ion battery.
Features
n
550mA, 0.7
, internal switch
n
Uses small surface mount components
n
Adjustable output voltage up to 20V
n
2.2V to 7V input range
n
Input undervoltage lockout
n
0.01A shutdown current
n
Small 5-Lead SOT-23 package
Applications
n
LCD Bias Supplies
n
White LED Back-Lighting
n
Handheld Devices
n
Digital Cameras
n
Portable Applications
Typical Application Circuit
20031501
FIGURE 1. Typical 20V Application
April 2003
LM2704
Micropower
Step-up
DC/DC
Converter
with
550mA
Peak
Current
Limit
2003 National Semiconductor Corporation
DS200315
www.national.com
Connection Diagram
Top View
20031502
SOT23-5
T
Jmax
= 125C,
JA
= 220C/W (Note 2)
Ordering Information
Order Number
Package Type
NSC Package Drawing
Top Mark
Supplied As
LM2704MF-ADJ
SOT23-5
MA05B
S28B
1000 Units, Tape and Reel
LM2704MFX-ADJ
SOT23-5
MA05B
S28B
3000 Units, Tape and Reel
Pin Description/Functions
Pin
Name
Function
1
SW
Power Switch input.
2
GND
Ground.
3
FB
Output voltage feedback input.
4
SHDN
Shutdown control input, active low.
5
V
IN
Analog and Power input.
SW(Pin 1): Switch Pin. This is the drain of the internal
NMOS power switch. Minimize the metal trace area con-
nected to this pin to minimize EMI.
GND(Pin 2): Ground Pin. Tie directly to ground plane.
FB(Pin 3): Feedback Pin. Set the output voltage by selecting
values for R1 and R2 using:
Connect the ground of the feedback network to an AGND
plane which should be tied directly to the GND pin.
SHDN(Pin 4): Shutdown Pin. The shutdown pin is an active
low control. Tie this pin above 1.1V to enable the device. Tie
this pin below 0.3V to turn off the device.
V
IN
(Pin 5): Input Supply Pin. Bypass this pin with a capacitor
as close to the device as possible.
LM2704
www.national.com
2
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
IN
7.5V
SW Voltage
21V
FB Voltage
2V
SHDN Voltage
7.5V
Maximum Junction Temp. T
J
(Note 2)
150C
Lead Temperature
(Soldering 10 sec.)
300C
Vapor Phase
(60 sec.)
215C
Infrared
(15 sec.)
220C
ESD Ratings (Note 3)
Human Body Model
Machine Model (Note 4)
2kV
200V
Operating Conditions
Junction Temperature
(Note 5)
-40C to +125C
Supply Voltage
2.2V to 7V
SW Voltage Max.
20.5V
Electrical Characteristics
(Note 5)
Specifications in standard type face are for T
J
= 25C and those in boldface type apply over the full Operating Temperature
Range (T
J
= -40C to +125C). Unless otherwise specified. V
IN
=2.2V.
Symbol
Parameter
Conditions
Min
(Note 5)
Typ
(Note 6)
Max
(Note 5)
Units
I
Q
Device Disabled
FB = 1.3V
40
70
A
Device Enabled
FB = 1.2V
235
300
Shutdown
SHDN = 0V
0.01
2.5
V
FB
Feedback Trip Point
1.189
1.237
1.269
V
I
CL
Switch Current Limit
490
420
550
610
620
mA
I
B
FB Pin Bias Current
FB = 1.23V (Note 7)
30
120
nA
V
IN
Input Voltage Range
2.2
7.0
V
R
DSON
Switch R
DSON
0.7
1.6
T
OFF
Switch Off Time
400
ns
I
SD
SHDN Pin Current
SHDN = V
IN
, T
J
= 25C
0
80
nA
SHDN = V
IN
, T
J
= 125C
15
SHDN = GND
0
I
L
Switch Leakage Current
V
SW
= 20V
0.05
5
A
UVP
Input Undervoltage Lockout
ON/OFF Threshold
1.8
V
V
FB
Hysteresis
Feedback Hysteresis
8
mV
SHDN
Threshold
SHDN low
0.7
0.3
V
SHDN High
1.1
0.7
JA
Thermal Resistance
220
C/W
Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to
be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, T
J
(MAX), the junction-to-ambient thermal resistance,
JA
,
and the ambient temperature, T
A
. See the Electrical Characteristics table for the thermal resistance. The maximum allowable power dissipation at any ambient
temperature is calculated using: P
D
(MAX) = (T
J(MAX)
- T
A
)/
JA
. Exceeding the maximum allowable power dissipation will cause excessive die temperature.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 k
resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin.
Note 4: ESD susceptibility using the machine model is 150V for SW pin.
Note 5: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100%
production tested or guaranteed through statistical analysis. 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 6: Typical numbers are at 25C and represent the most likely norm.
Note 7: Feedback current flows into the pin.
LM2704
www.national.com
3
PDF 
ZIP
