NSC LM2681M6X, LM2681M6 Datasheet
LM2681
Switched Capacitor Voltage Converter
LM2681 Switched Capacitor Voltage Converter
March 1999
General Description
The LM2681 CMOS charge-pump voltage converter operates asa voltage doubler for an input voltage in the range of
+2.5V to +5.5V. Two low cost capacitors and a diode
(needed during start-up) is used in this circuit to provide up
to 20 mA of output current. The LM2681 can also work as a
voltage divider to split a voltage in the range of +1.8V to
+11V in half.
The LM2681 operates at 160 kHz oscillator frequency to reduce output resistance and voltage ripple. With an operating
current of only550 µA (operating efficiency greaterthan 90
with most loads) the LM2681 provides ideal performance for
battery powered systems. The device is in SOT-23-6 package.
Basic Application Circuits
Voltage Doubler
Splitting Vinin Half
Features
n Doubles or Splits Input Supply Voltage
n SOT23-6 Package
n 15Ω Typical Output Impedance
n 90%Typical Conversion Efficiency at 20 mA
Applications
n Cellular Phones
n Pagers
n PDAs
%
n Operational Amplifier Power Suppliers
n Interface Power Suppliers
n Handheld Instruments
DS100965-1
DS100965-2
© 1999 National Semiconductor Corporation DS100965 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact theNational Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V+ to GND, or GND to OUT) 5.8V
V+ and OUT Continuous Output Current 30 mA
Output Short-Circuit Duration to GND (Note 2) 1 sec.
Continuous Power
Dissipation (T
=
A
25˚C)(Note 3)
600 mW
T
(Note 3) 150˚C
JMax
θ
(Note 3) 210˚C/W
JA
Operating Junction Temperature
−40˚ to 85˚C
Range
Storage Temperature Range −65˚C to +150˚C
Lead Temp. (Soldering, 10 seconds) 300˚C
ESD Rating 2kV
Electrical Characteristics
Limits in standard typeface are for T
less otherwise specified: V+=5V, C
Symbol Parameter Condition Min Typ Max Units
V+ Supply Voltage 2.5 5.5 V
I
Q
I
L
R
SW
R
OUT
f
OSC
f
SW
P
EFF
V
OEFF
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: OUTmay be shorted to GND for onesecond without damage. However, shorting OUT to V+ may damage the device and should be avoided.Also, for temperatures above 85˚C, OUT must not be shorted to GND or V+, or device may be damaged.
Note 3: The maximum allowable power dissipation is calculated by using P
ambient temperature, and θ
Note 4: Inthetestcircuit, capacitors C
voltage and efficiency.
Note 5: Specifiedoutputresistance includes internal switch resistance and capacitor ESR. See thedetails in the application information for positive voltage doubler.
Note 6: The output switches operate at one half of the oscillator frequency, f
Supply Current No Load 550 1000 µA
Output Current 20 mA
Sum of the R
internal MOSFET switches
ds(on)
Output Resistance (Note 5) I
Oscillator Frequency (Note 6) 80 160 kHz
Switching Frequency (Note 6) 40 80 kHz
Power Efficiency RL(1.0k) between GND and
Voltage Conversion Efficiency No Load 99 99.96
is the junction-to-ambient thermal resistance of the specified package.
JA
=
25˚C, and limits in boldface type apply over the full operating temperature range. Un-
J
=
=
C
3.3 µF. (Note 4)
1
2
of the four
and C2are 3.3 µF, 0.3Ω maximum ESR capacitors. CapacitorswithhigherESRwillincreaseoutput resistance, reduce output
1
=
I
20 mA 8 16 Ω
L
=
20 mA 15 40 Ω
L
OUT
=
I
20 mA to GND 90
L
DMax
OSC
=
=
(T
JMax−TA
2f
SW
)/θJA, where T
.
86 93
is the maximum junction temperature, TAis the
JMax
%
%
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Test Circuit
FIGURE 1. LM2681 Test Circuit
Typical Performance Characteristics
DS100965-3
(Circuit of Figure 1, V+=5V unless otherwise specified)
Supply Current vs
Supply Voltage
Output Source
Resistance vs Supply
Voltage
DS100965-4
Supply Current vs
Temperature
DS100965-5
Output Source
Resistance vs
Temperature
DS100965-6
DS100965-7
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