LM2682 [NSC]
Switched Capacitor Voltage Doubling Inverter; 开关电容电压倍增逆变器
| 型号： | LM2682 |
| 厂家： | 
National Semiconductor |
| 描述： | Switched Capacitor Voltage Doubling Inverter |
| 文件： | 总8页 (文件大小：136K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
November 1999
LM2682
Switched Capacitor Voltage Doubling Inverter
General Description
Features
n Inverts then doubles input supply voltage
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 ef-
ficiency greater than 90% with most loads, the LM2682 pro-
vides ideal performance for battery powered systems. The
LM2682 offers a switching frequency of 6 kHz.
n Small MSOP-8 package (mini SO-8) and SO-8 package
n 90Ω typical output impedance
n 94% typical power efficiency at 10 mA
Applications
n LCD contrast biasing
n GaAs power amplifier biasing
n Interface power supplies
n Handheld instrumentation
n Laptop computers and PDAs
Typical Operating Circuit and Pin Configuration
8-Pin MSOP
or 8-Pin SOIC
DS100997-2
DS100997-1
Ordering Information
Order Number
LM2682MM
LM2682MMX
LM2682M
Package
MSOP-8
MSOP-8
SO-8
Package Number
MUA08A
MUA08A
M08A
Package Marking
S11A
Supplied As
Tape and Reel (1000 units/reel)
Tape and Reel (3500 units/reel)
Rail (95 units/rail)
S11A
LM2682M
LM2682M
LM2682MX
SO-8
M08A
Tape and Reel (2500 units/reel)
© 1999 National Semiconductor Corporation
DS100997
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
MSOP-8
SO-8
300 mW
470 mW
+150˚C
TJMAX
Operating Ratings
Input Voltage (VIN
)
+5.8V
1V/µsec
VIN dV/dT
ESD Susceptibility (Note 3)
VOUT
−11.6V
Human Body Model
Machine Model
2 kV
200V
VOUT Short-Circuit Duration
Storage Temperature
Continuous
−65˚C to +150˚C
+300˚C
Ambient Temp. Range
Junction Temp. Range
−40˚C to +85˚C
−40˚C to +125˚C
Lead Temperature Soldering
Power Dissipation (Note 2)
LM2682
=
=
=
=
Electrical Characteristics VIN 5V and C1 C2 C3 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 TA
=
25˚C.
Symbol
VIN
Parameter
Conditions
Min
2.0
Typical
Max
5.5
Units
(Note 4)
=
Supply Voltage Range
RL 2 kΩ
V
IIN
Supply Current
Open Circuit, No Load
150
90
300
400
µA
=
ROUT
VOUT Source Resistance
IL 10 mA
150
200
250
30
Ω
=
=
IL 5 mA, VIN 2 V
110
12
Ω
kHz
kHz
%
fOSC
Oscillator Frequency
Switching Frequency
Power Efficiency
(Note 5)
fSW
(Note 5)
6
15
=
ηPOWER
ηVOLTAGE
RL 2k (Note 6)
90
93
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 T 85˚C) and is limited by T
(maximum junction tempera-
A
JMAX
ture), θ
(junction to ambient thermal resistance) and T (ambient temperature). θ
A J-A
is 140˚C/W for the SO-8 package and 220˚C/W for the MSOP-8 package. The
J-A
maximum power dissipation at any temperature is:
=
PDiss
(T
− T )/θ up to the value listed in the Absolute Maximum Ratings.
J-A
MAX
JMAX
A
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 200pF capacitor discharged di-
rectly 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, f
OSC
2f
.
SW
Note 6: The minimum specification is guaranteed by design and is not tested.
Pin Description
Pin Number
Symbol
C1−
Description
1
2
3
4
5
6
7
8
Capacitor C1 negative terminal
Capacitor C2 positive terminal
Capacitor C2 negative terminal
Negative output voltage (−2VIN
Device ground
C2+
C2−
VOUT
GND
VIN
)
Power supply voltage
C1+
Capacitor C1 positive terminal
No Connection
NC
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2
=
=
Typical Performance Charactistics VIN 5V and TA 25˚C unless otherwise noted.
Output Resistance vs Input Voltage
Output Voltage vs Load Current
DS100997-7
DS100997-6
Supply Current vs Input Voltage
Output Resistance vs Temperature
DS100997-8
DS100997-9
Output Voltage Ripple vs Load Current
DS100997-10
3
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Basic Application Circuits
DS100997-3
FIGURE 1. Doubling Voltage Inverter
DS100997-4
FIGURE 2. +5V to −5V Regulated Voltage Converter
Output resistance is typically 90Ω with 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 re-
duce 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.
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 cir-
cuit requires only three external capacitors and is connected
as shown in Figure 1. It is important to keep in mind that the
efficiency of the circuit is determined by the output resis-
tance. A derivation of the output resistance is shown below:
The amount of output voltage ripple is determined by the out-
put capacitor C3 and the output current as shown in this
equation:
=
ROUT
2(RSW1+RSW2+ESRC1+RSW3+RSW4+ESRC2) +
2(RSW1+RSW2+ESRC1+RSW3+RSW4+ESRC2) +
1/(fOSCxC1) + 1/(fOSCxC2) + ESRC3
=
VRIPPLE P-P IOUT x (2xESRC3 + 1/[2x(fOSCxC3)])
Using the assumption that all four switches have the same
ON resistance our equation becomes:
Once again a larger capacitor with smaller ESR will give bet-
ter results.
=
ROUT
16RSW + 4ESRC1 + 4ESRC2 + ESRC3
1/(fOSCxC1) + 1/(fOSCxC2)
+
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4
Paralleling Devices
Application Information (Continued)
Any number of devices can be paralleled to reduce the out-
put 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 re-
sistance of one device supplying 10 mA.
+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 out-
put by the PSRR of the op-amp used.
DS100997-5
FIGURE 3. Paralleling Devices
5
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Physical Dimensions inches (millimeters) unless otherwise noted
8 Lead (0.150” Wide) Molded Small Outline Package, JEDEC
NS Package Number M08A
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6
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Surface Mount Mini SO-8 Package
NS Package Number MUA08A
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