National LM2705MFX-ADJ Schematic [ru]
April 2003
LM2705
Micropower Step-up DC/DC Converter with 150mA Peak
Current Limit
LM2705 Micropower Step-up DC/DC Converter with 150mA Peak Current Limit
General Description
The LM2705 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 spaceconscious portable applications. The LM2705 is ideal for
LCD panels requiring low current and high efficiency as well
as white LED applications for cellular phone back-lighting.
The LM2705 can drive up to 3 white LEDs from a single
Li-Ion battery. The low peak inductor current of the LM2705
makes it ideal for USB applications.
Typical Application Circuit
Features
n 150mA, 0.7Ω, 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 0.01µA 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
20039701
FIGURE 1. Typical 20V Application
© 2003 National Semiconductor Corporation DS200397 www.national.com
Connection Diagram
LM2705
Top View
SOT23-5
= 125˚C, θJA= 220˚C/W (Note 2)
T
Jmax
20039702
Ordering Information
Order Number Package Type NSC Package Drawing Top Mark Supplied As
LM2705MF-ADJ SOT23-5 MA05B S59B 1000 Units, Tape and Reel
LM2705MFX-ADJ SOT23-5 MA05B S59B 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
5V
SW(Pin 1): Switch Pin. This is the drain of the internal
NMOS power switch. Minimize the metal trace area connected 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:
IN
Shutdown control input, active low.
Analog and Power input.
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
as close to the device as possible.
(Pin 5): Input Supply Pin. Bypass this pin with a capacitor
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LM2705
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
Infrared
(15 sec.) 220˚C
ESD Ratings (Note 3)
Human Body Model
Machine Model (Note 4)
200V
SW Voltage 21V
FB Voltage 2V
SHDN Voltage
Maximum Junction Temp. T
J
7.5V
150˚C
(Note 2)
Lead Temperature
(Soldering 10 sec.) 300˚C
Operating Conditions
Junction Temperature
(Note 5) −40˚C to +125˚C
Supply Voltage 2.2V to 7V
SW Voltage Max. 20.5V
Vapor Phase
(60 sec.) 215˚C
Electrical Characteristics
Specifications in standard type face are for TJ= 25˚C and those in boldface type apply over the full Operating Temperature
Range (T
Symbol Parameter Conditions
I
Q
V
FB
I
CL
I
B
V
IN
R
DSON
T
OFF
I
SD
I
L
UVP Input Undervoltage Lockout ON/OFF Threshold 1.8 V
V
FB
Hysteresis
SHDN
Threshold
θ
JA
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
and the ambient temperature, T
temperature is calculated using: P
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ 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 25˚C and represent the most likely norm.
Note 7: Feedback current flows into the pin.
= −40˚C to +125˚C). Unless otherwise specified VIN=2.2V.
J
Min
(Note 5)
Typ
(Note 6)
Max
(Note 5)
Device Disabled FB = 1.3V 40 70
Shutdown SHDN = 0V
0.01 2.5
FeedbackTrip Point 1.189 1.237 1.269 V
Switch Current Limit 110
100
150 175
180
FB Pin Bias Current FB = 1.23V (Note 7) 30 120 nA
Input Voltage Range 2.2 7.0 V
Switch R
DSON
0.7 1.6 Ω
Switch Off Time 400 ns
SHDN Pin Current SHDN = VIN,TJ= 25˚C 080
= 125˚C 15
IN,TJ
SHDN = GND
0
Switch Leakage Current VSW= 20V 0.05 5 µA
Feedback Hysteresis 8 mV
SHDN low
SHDN High
1.1 0.7
0.7 0.3
Thermal Resistance 220 ˚C/W
(MAX), the junction-to-ambient thermal resistance, θJA,
. See the Electrical Characteristics table for the thermal resistance. The maximum allowable power dissipation at any ambient
A
(MAX) = (T
D
J(MAX)−TA
)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature.
J
Units
mA
2kV
µADevice Enabled FB = 1.2V 235 300
nASHDN = V
V
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Typical Performance Characteristics
LM2705
Enable Current vs V
IN
(Part Switching)
20039705 20039706
Efficiency vs Load Current Efficiency vs Load Current
Disable Current vs V
(Part Not Switching)
IN
SHDN Threshold vs V
20039724
IN
20039713
Switch Current Limit vs V
20039725
IN
20039737
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