LM2682
LM2682 Switched Capacitor Voltage Doubling Inverter
Literature Number: SNVS044A
LM2682
Switched Capacitor Voltage Doubling Inverter
General Description
The LM2682 is a CMOS charge-pump voltage inverter ca-
pable of converting positive voltage in the range of +2.0V to
+5.5V to the corresponding doubled negative voltage of
−4.0V to −11.0V respectively. The LM2682 uses three low
cost capacitors to provide 10 mA of output current without
the cost, size, and EMI related to inductor based circuits.
With an operating current of only 150 µA and an operating
efficiency greater than 90% with most loads, the LM2682
provides ideal performance for battery powered systems.
The LM2682 offers a switching frequency of 6 kHz.
Features
nInverts then doubles input supply voltage
nSmall MSOP-8 package (mini SO-8) and SO-8 package
n90Ωtypical output impedance
n94% typical power efficiency at 10 mA
Applications
nLCD contrast biasing
nGaAs power amplifier biasing
nInterface power supplies
nHandheld instrumentation
nLaptop computers and PDAs
Typical Operating Circuit and Pin Configuration
8-Pin MSOP
or 8-Pin SOIC
10099701
10099702
Ordering Information
Order Number Package Package Number Package Marking Supplied As
LM2682MM MSOP-8 MUA08A S11A Tape and Reel (1000 units/reel)
LM2682MMX MSOP-8 MUA08A S11A Tape and Reel (3500 units/reel)
LM2682M SO-8 M08A LM2682M Rail (95 units/rail)
LM2682MX SO-8 M08A LM2682M Tape and Reel (2500 units/reel)
November 1999
LM2682 Switched Capacitor Voltage Doubling Inverter
© 2004 National Semiconductor Corporation DS100997 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage (V
IN
) +5.8V
V
IN
dV/dT 1V/µsec
V
OUT
−11.6V
V
OUT
Short-Circuit Duration Continuous
Storage Temperature −65˚C to +150˚C
Lead Temperature Soldering +300˚C
Power Dissipation (Note 2)
MSOP-8 300 mW
SO-8 470 mW
T
JMAX
+150˚C
Operating Ratings
ESD Susceptibility (Note 3)
Human Body Model
Machine Model
2kV
200V
Ambient Temp. Range −40˚C to +85˚C
Junction Temp. Range −40˚C to +125˚C
LM2682
Electrical Characteristics V
IN
= 5V and C
1
=C
2
=C
3
= 3.3µF unless otherwise specified. Limits with bold
typeface apply over the full operating ambient temperature range, −40˚C to +85˚C, limits with standard typeface apply for T
A
= 25˚C.
Symbol Parameter Conditions Min Typical
(Note 4)
Max Units
V
IN
Supply Voltage Range R
L
=2kΩ2.0 5.5 V
I
IN
Supply Current Open Circuit, No Load 150 300
400
µA
R
OUT
V
OUT
Source Resistance I
L
=10mA 90 150 Ω
200
I
L
=5 mA, V
IN
=2 V 110 250 Ω
f
OSC
Oscillator Frequency (Note 5) 12 30 kHz
f
SW
Switching Frequency (Note 5) 6 15 kHz
η
POWER
Power Efficiency R
L
= 2k (Note 6) 90 93 %
η
VOLTAGE
Voltage Conversion Efficiency 99.9 %
Note 1: Absolute Maximum Ratings are those values beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device
is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The maximum power dissipation must be de-rated at elevated temperatures (only needed for TA>85˚C) and is limited by TJMAX (maximum junction
temperature), θJ-A (junction to ambient thermal resistance) and TA(ambient temperature). θJ-A is 140˚C/W for the SO-8 package and 220˚C/W for the MSOP-8
package. The maximum power dissipation at any temperature is:
PDissMAX =(T
JMAX −T
A)/θJ-A up to the value listed in the Absolute Maximum Ratings.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩresistor into each pin. The machine model is a 200pF capacitor discharged
directly into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely norm.
Note 5: The output switches operate at one half of the oscillator frequency, fOSC =2f
SW.
Note 6: The minimum specification is guaranteed by design and is not tested.
Pin Description
Pin Number Symbol Description
1C
1
− Capacitor C
1
negative terminal
2C
2
+ Capacitor C
2
positive terminal
3C
2
− Capacitor C
2
negative terminal
4V
OUT
Negative output voltage (−2V
IN
)
5 GND Device ground
6V
IN
Power supply voltage
7C
1
+ Capacitor C
1
positive terminal
8 NC No Connection
LM2682
www.national.com 2
Typical Performance Charactistics
V
IN
= 5V and T
A
= 25˚C unless otherwise noted.
Output Resistance vs Input Voltage Output Voltage vs Load Current
10099706 10099707
Supply Current vs Input Voltage Output Resistance vs Temperature
10099708 10099709
Output Voltage Ripple vs Load Current
10099710
LM2682
www.national.com3
Basic Application Circuits
Application Information
VOLTAGE DOUBLING INVERTER
The main application of the LM2682 is to generate a nega-
tive voltage that is twice the positive input voltage. This
circuit requires only three external capacitors and is con-
nected as shown in Figure 1. It is important to keep in mind
that the efficiency of the circuit is determined by the output
resistance. A derivation of the output resistance is shown
below:
R
OUT
= 2(R
SW1
+R
SW2
+ESR
C1
+R
SW3
+R
SW4
+ESR
C2
)+
2(R
SW1
+R
SW2
+ESR
C1
+R
SW3
+R
SW4
+ESR
C2
)+
1/(f
OSC
xC1) + 1/(f
OSC
xC2) + ESR
C3
Using the assumption that all four switches have the same
ON resistance our equation becomes:
R
OUT
= 16R
SW
+ 4ESR
C1
+ 4ESR
C2
+ ESR
C3
+
1/(f
OSC
xC1) + 1/(f
OSC
xC2)
Output resistance is typically 90Ωwith an input voltage of
+5V, an operating temperature of 25˚C, and using low ESR
3.3 µF capacitors. This equation shows the importance of
capacitor selection. Large value, low ESR capacitors will
reduce the output resistance significantly but will also require
a larger overall circuit. Smaller capacitors will take up less
space but can lower efficiency greatly if the ESR is large.
Also to be considered is that C1 must be rated at 6 VDC or
greater while C2 and C3 must be rated at 12 VDC or greater.
10099703
FIGURE 1. Doubling Voltage Inverter
10099704
FIGURE 2. +5V to −5V Regulated Voltage Converter
LM2682
www.national.com 4
Application Information (Continued)
The amount of output voltage ripple is determined by the
output capacitor C3 and the output current as shown in this
equation:
V
RIPPLE P-P
=I
OUT
x (2xESR
C3
+ 1/[2x(f
OSC
xC3)])
Once again a larger capacitor with smaller ESR will give
better results.
+5V TO −5V REGULATED VOLTAGE CONVERTER
Another application in which the LM2682 can be used is for
generating a −5V regulated supply from a +5V unregulated
supply. This involves using an op-amp and a reference and
is connected as shown in Figure 2. The LM358 op-amp was
chosen for its low cost and versatility and the LM4040-5.0
reference was chosen for its low bias current requirement.
Of course other combinations may be used at the designer’s
discretion to fit accuracy, efficiency, and cost requirements.
With this configuration the circuit is well regulated and is still
capable of providing nearly 10 mA of output current. With a 9
mA load the circuit can typically maintain 5% regulation on
the output voltage with the input varying anywhere from 4.5V
to the maximum of 5.5V. With less load the results are even
better. Voltage ripple concerns are reduced in this case since
the ripple at the output of the LM2682 is reduced at the
output by the PSRR of the op-amp used.
PARALLELING DEVICES
Any number of devices can be paralleled to reduce the
output resistance. As shown in Figure 3, each device must
have its own pumping capacitors, C1 and C2, but only one
shared output capacitor is required. The effective output
resistance is the output resistance of one device divided by
the number of devices used in parallel. Paralleling devices
also gives the capability of increasing the maximum output
current. The maximum output current now becomes the
maximum output current for one device multiplied by the
number of devices used in parallel. For example, if you
parallel two devices you can get 20 mA of output current and
have half the output resistance of one device supplying 10
mA.
10099705
FIGURE 3. Paralleling Devices
LM2682
www.national.com5
Physical Dimensions inches (millimeters) unless otherwise noted
8 Lead (0.150” Wide) Molded Small Outline Package, JEDEC
NS Package Number M08A
Surface Mount Mini SO-8 Package
NS Package Number MUA08A
LM2682
www.national.com 6
Notes
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
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1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
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LM2682 Switched Capacitor Voltage Doubling Inverter
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