LM2681
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SNVS042B –MARCH 1999–REVISED MAY 2013
LM2681 Switched Capacitor Voltage Converter
Check for Samples: LM2681
1FEATURES DESCRIPTION
The LM2681 CMOS charge-pump voltage converter
2• Doubles or Splits Input Supply Voltage operates as a voltage doubler for an input voltage in
• SOT-23 6-Lead Package the range of +2.5V to +5.5V. Two low cost capacitors
• 15ΩTypical Output Impedance and a diode (needed during start-up) is used in this
circuit to provide up to 20 mA of output current. The
• 90% Typical Conversion Efficiency at 20 mA LM2681 can also work as a voltage divider to split a
voltage in the range of +1.8V to +11V in half.
APPLICATIONS The LM2681 operates at 160 kHz oscillator frequency
• Cellular Phones to reduce output resistance and voltage ripple. With
• Pagers an operating current of only 550 µA (operating
• PDAs efficiency greater than 90% with most loads) the
LM2681 provides ideal performance for battery
• Operational Amplifier Power Suppliers powered systems. The device is in a SOT-23, 6-lead
• Interface Power Suppliers package.
• Handheld Instruments
Basic Application Circuits
Voltage Doubler
Splitting Vin in Half
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 1999–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
LM2681
SNVS042B –MARCH 1999–REVISED MAY 2013
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings(1)(2)
V+ to GND Voltage 5.8V
OUT to GND Voltage 11.6V
OUT to V+ Voltage 5.8V
V+ and OUT Continuous Output Current 30 mA
Output Short-Circuit Duration to GND(3) 1 sec.
Continuous Power Dissipation (TA= 25°C)(4) 600 mW
TJMax(4) 150°C
θJA(4) 210°C/W
Operating Junction Temperature Range −40° to 85°C
Storage Temperature Range −65°C to +150°C
Lead Temp. (Soldering, 10 seconds) 300°C
ESD Rating 2kV
(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.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(3) OUT may be shorted to GND for one second 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.
(4) The maximum allowable power dissipation is calculated by using PDMax = (TJMax −TA)/θJA, where TJMax is the maximum junction
temperature, TAis the ambient temperature, and θJA is the junction-to-ambient thermal resistance of the specified package.
Electrical Characteristics
Limits in standard typeface are for TJ= 25°C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: V+ = 5V, C1= C2= 3.3 μF.(1)
Symbol Parameter Condition Min Typ Max Units
V+ Supply Voltage 2.5 5.5 V
IQSupply Current No Load 550 1000 µA
ILOutput Current 20 mA
RSW Sum of the Rds(on)of the four internal IL= 20 mA 8 16 Ω
MOSFET switches
ROUT Output Resistance(2) IL= 20 mA 15 40 Ω
fOSC Oscillator Frequency See(3) 80 160 kHz
fSW Switching Frequency See(3) 40 80 kHz
PEFF Power Efficiency RL(1.0k) between GND and OUT 86 93 %
IL= 20 mA to GND 90
VOEFF Voltage Conversion Efficiency No Load 99 99.96 %
(1) In the test circuit, capacitors C1and C2are 3.3 µF, 0.3Ωmaximum ESR capacitors. Capacitors with higher ESR will increase output
resistance, reduce output voltage and efficiency.
(2) Specified output resistance includes internal switch resistance and capacitor ESR. See POSITIVE VOLTAGE DOUBLER
(3) The output switches operate at one half of the oscillator frequency, fOSC = 2fSW.
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Typical Performance Characteristics
(Circuit of Figure 1, V+ = 5V unless otherwise specified)
Supply Current vs Supply Current vs
Supply Voltage Temperature
Figure 2. Figure 3.
Output Source
Resistance Output Source
vs Resistance
Supply vs
Voltage Temperature
Figure 4. Figure 5.
Efficiency
Output Voltage Drop vs
vs Load Current Load Current
Figure 6. Figure 7.
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Typical Performance Characteristics (continued)
(Circuit of Figure 1, V+ = 5V unless otherwise specified)
Oscillator Frequency vs Oscillator Frequency vs
Supply Voltage Temperature
Figure 8. Figure 9.
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CONNECTION DIAGRAM
Figure 10. SOT-23, 6-Lead Package – Top View Figure 11. Actual Size
See Package Number DBV
PIN DESCRIPTION
Function
Pin Name Voltage Doubler Voltage Split
1 V+ Power supply positive voltage input Positive voltage output
2 GND Power supply ground input Same as doubler
3 CAP−Connect this pin to the negative terminal of the charge- Same as doubler
pump capacitor
4 GND Power supply ground input Same as doubler
5 OUT Positive voltage output Power supply positive voltage input
6 CAP+ Connect this pin to the positive terminal of the charge-pump Same as doubler
capacitor
Circuit Description
The LM2681 contains four large CMOS switches which are switched in a sequence to double the input supply
voltage. Energy transfer and storage are provided by external capacitors. Figure 12 illustrates the voltage
conversion scheme. When S2and S4are closed, C1charges to the supply voltage V+. During this time interval,
switches S1and S3are open. In the next time interval, S2and S4are open; at the same time, S1and S3are
closed, the sum of the input voltage V+ and the voltage across C1gives the 2V+ output voltage when there is no
load. The output voltage drop when a load is added is determined by the parasitic resistance (Rds(on) of the
MOSFET switches and the ESR of the capacitors) and the charge transfer loss between capacitors. Details will
be discussed in the APPLICATION INFORMATION section.
Figure 12. Voltage Doubling Principle
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APPLICATION INFORMATION
POSITIVE VOLTAGE DOUBLER
The main application of the LM2681 is to double the input voltage. The range of the input supply voltage is 2.5V
to 5.5V.
The output characteristics of this circuit can be approximated by an ideal voltage source in series with a
resistance. The voltage source equals 2V+. The output resistance Rout is a function of the ON resistance of the
internal MOSFET switches, the oscillator frequency, the capacitance and ESR of C1and C2. Since the switching
current charging and discharging C1is approximately twice as the output current, the effect of the ESR of the
pumping capacitor C1will be multiplied by four in the output resistance. The output capacitor C2is charging and
discharging at a current approximately equal to the output current, therefore, its ESR only counts once in the
output resistance. A good approximation of Rout is:
(1)
where RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 12.
The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the
output capacitor C2:
(2)
High capacitance, low ESR capacitors can reduce both the output reslistance and the voltage ripple.
The Schottky diode D1is only needed for start-up. The internal oscillator circuit uses the OUT pin and the GND
pin. Voltage across OUT and GND must be larger than 1.8V to insure the operation of the oscillator. During start-
up, D1is used to charge up the voltage at the OUT pin to start the oscillator; also, it protects the device from
turning-on its own parasitic diode and potentially latching-up. Therefore, the Schottky diode D1should have
enough current carrying capability to charge the output capacitor at start-up, as well as a low forward voltage to
prevent the internal parasitic diode from turning-on. A Schottky diode like 1N5817 can be used for most
applications. If the input voltage ramp is less than 10V/ms, a smaller Schottky diode like MBR0520LT1 can be
used to reduce the circuit size.
SPLIT V+ IN HALF
Another interesting application shown in the Basic Application Circuits is using the LM2681 as a precision voltage
divider. . This circuit can be derived from the voltage doubler by switching the input and output connections. In
the voltage divider, the input voltage applies across the OUT pin and the GND pin (which are the power rails for
the internal oscillator), therefore no start-up diode is needed. Also, since the off-voltage across each switch
equals Vin/2, the input voltage can be raised to +11V.
CAPACITOR SELECTION
As discussed in the POSITIVE VOLTAGE DOUBLER section, the output resistance and ripple voltage are
dependent on the capacitance and ESR values of the external capacitors. The output voltage drop is the load
current times the output resistance, and the power efficiency is
(3)
Where IQ(V+) is the quiescent power loss of the IC device, and IL2Rout is the conversion loss associated with the
switch on-resistance, the two external capacitors and their ESRs.
The selection of capacitors is based on the specifications of the dropout voltage (which equals Iout Rout), the
output voltage ripple, and the converter efficiency. Low ESR capacitors are recommended to maximize efficiency,
reduce the output voltage drop and voltage ripple.
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SNVS042B –MARCH 1999–REVISED MAY 2013
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Low ESR Capacitor Manufacturers
Manufacturer Phone Capacitor Type
Nichicon Corp. (708)-843-7500 PL & PF series, through-hole aluminum electrolytic
AVX Corp. (803)-448-9411 TPS series, surface-mount tantalum
Sprague (207)-324-4140 593D, 594D, 595D series, surface-mount tantalum
Sanyo (619)-661-6835 OS-CON series, through-hole aluminum electrolytic
Murata (800)-831-9172 Ceramic chip capacitors
Taiyo Yuden (800)-348-2496 Ceramic chip capacitors
Tokin (408)-432-8020 Ceramic chip capacitors
Other Applications
PARALLELING DEVICES
Any number of LM2681s can be paralleled to reduce the output resistance. Each device must have its own
pumping capacitor C1, while only one output capacitor Cout is needed as shown in Figure 13. The composite
output resistance is:
(4)
Figure 13. Lowering Output Resistance by Paralleling Devices
CASCADING DEVICES
Cascading the LM2681s is an easy way to produce a greater voltage (A two-stage cascade circuit is shown in
Figure 14).
The effective output resistance is equal to the weighted sum of each individual device:
Rout = 1.5Rout_1 + Rout_2 (5)
Note that, the increasing of the number of cascading stages is practically limited since it significantly reduces the
efficiency, increases the output resistance and output voltage ripple.
Figure 14. Increasing Output Voltage by Cascading Devices
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REGULATING VOUT
It is possible to regulate the output of the LM2681 by use of a low dropout regulator (such as LP2980-5.0). The
whole converter is depicted in Figure 15.
A different output voltage is possible by use of LP2980-3.3, LP2980-3.0, or LP2980-adj.
Note that, the following conditions must be satisfied simultaneously for worst case design:
2Vin_min >Vout_min +Vdrop_max (LP2980) + Iout_max × Rout_max (LM2681) (6)
2Vin_max < Vout_max +Vdrop_min (LP2980) + Iout_min × Rout_min (LM2681) (7)
Figure 15. Generate a Regulated +5V from +3V Input Voltage
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REVISION HISTORY
Changes from Revision A (May 2013) to Revision B Page
• Changed layout of National Data Sheet to TI format ............................................................................................................ 9
10 Submit Documentation Feedback Copyright © 1999–2013, Texas Instruments Incorporated
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PACKAGE OPTION ADDENDUM
www.ti.com 4-Nov-2016
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM2681M6/NOPB ACTIVE SOT-23 DBV 6 1000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 S10A
LM2681M6X/NOPB ACTIVE SOT-23 DBV 6 3000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 S10A
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
PACKAGE OPTION ADDENDUM
www.ti.com 4-Nov-2016
Addendum-Page 2
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM2681M6/NOPB SOT-23 DBV 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2681M6X/NOPB SOT-23 DBV 6 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
PACKAGE MATERIALS INFORMATION
www.ti.com 20-Dec-2016
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2681M6/NOPB SOT-23 DBV 6 1000 210.0 185.0 35.0
LM2681M6X/NOPB SOT-23 DBV 6 3000 210.0 185.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 20-Dec-2016
Pack Materials-Page 2
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