LM2664M6X - NATIONAL SEMICONDUCTOR

LM2664

LM2664 Switched Capacitor Voltage Converter

Literature Number: SNVS005C

LM2664

Switched Capacitor Voltage Converter

General Description

The LM2664 CMOS charge-pump voltage converter inverts

a positive voltage in the range of +1.8V to +5.5V to the

corresponding negative voltage of −1.8V to −5.5V. The

LM2664 uses two low cost capacitors to provide up to 40 mA

of output current.

The LM2664 operates at 160 kHz oscillator frequency to

reduce output resistance and voltage ripple. With an operat-

ing current of only 220 µA (operating efficiency greater than

91% with most loads) and 1 µA typical shutdown current, the

LM2664 provides ideal performance for battery powered

systems. The device is in SOT-23-6 package.

Features

nInverts Input Supply Voltage

nSOT23-6 Package

n12ΩTypical Output Impedance

n91% Typical Conversion Efficiency at 40 mA

n1µA Typical Shutdown Current

Applications

nCellular Phones

nPagers

nPDAs

nOperational Amplifier Power Suppliers

nInterface Power Suppliers

nHandheld Instruments

Basic Application Circuits

Voltage Inverter

10003101

+5V to −10V Converter

10003125

September 2005

LM2664 Switched Capacitor Voltage Converter

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage (V+ to GND, or GND to OUT) 5.8V

SD (GND − 0.3V) to (V+ +

0.3V)

V+ and OUT Continuous Output Current 50 mA

Output Short-Circuit Duration to GND (Note 2) 1 sec.

Continuous Power

Dissipation (T

= 25˚C)(Note 3)

600 mW

JMax

(Note 3) 150˚C

(Note 3) 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

Electrical Characteristics

Limits in standard typeface are for T

= 25˚C, and limits in boldface type apply over the full operating temperature range. Un-

less otherwise specified: V+ = 5V, C

= 3.3 µF. (Note 4)

Symbol

Parameter Condition

Min

(Note 5)

Typ

(Note 6)

Max

(Note 5) Units

V+ Supply Voltage 1.8 5.5 V

Supply Current No Load 220 500 µA

Shutdown Supply Current 1 µA

Shutdown Pin Input Voltage Normal Operation 2.0

(Note 7) V

Shutdown Mode 0.8

(Note 8)

Output Current 40 mA

Sum of the R

ds(on)

of the four

internal MOSFET switches

=40mA 4 8Ω

OUT

Output Resistance (Note 9) I

=40mA 12 25 Ω

OSC

Oscillator Frequency (Note 10) 80 160 kHz

Switching Frequency (Note 10) 40 80 kHz

EFF

Power Efficiency R

(1.0k) between GND and

OUT

90 94

=40mAtoGND 91

OEFF

Voltage Conversion Efficiency No Load 99 99.96 %

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: 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.

Note 3: The maximum allowable power dissipation is calculated by using PDMax =(T

JMax −T

A)/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.

Note 4: 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.

Note 5: Min. and Max. limits are guaranteed by design, test, or statistical analysis.

Note 6: Typical numbers are not guaranteed but represent the most likely norm.

Note 7: The minimum input high for the shutdown pin equals 40% of V+.

Note 8: The maximum input low for the shutdown pin equals 20% of V+.

Note 9: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for simple negative voltage

converter.

Note 10: The output switches operate at one half of the oscillator frequency, fOSC =2f

SW.

LM2664

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Test Circuit

Typical Performance Characteristics

(Circuit of Figure 1, V+ = 5V unless otherwise specified)

Supply Current vs

Supply Voltage

Supply Current vs

Temperature

10003121 10003113

Output Source

Resistance vs Supply

Voltage

Output Source

Resistance vs

Temperature

10003114 10003115

10003103

*C1and C2are 3.3 µF, SC series OS-CON capacitors.

FIGURE 1. LM2664 Test Circuit

LM2664

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Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified)

(Continued)

Output Voltage Drop

vs Load Current

Efficiency vs

Load Current

10003116 10003117

Oscillator Frequency vs

Supply Voltage

Oscillator Frequency vs

Temperature

10003118 10003119

Shutdown Supply

Current vs

Temperature

10003120

LM2664

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Connection Diagrams

6-Lead Small Outline Package (M6)

10003104

Top View With Package Marking

10003122

Actual Size

Ordering Information

Order Number Package Number Package Marking Supplied as

LM2664M6 MA06A SO3A (Note 11) Tape and Reel (1000 units/rail)

LM2664M6X MA06A SO3A (Note 11) Tape and Reel (3000 units/rail)

Note 11: The first letter "S" identifies the part as a switched capacitor converter. The next two numbers are the device number. The fourth letter "A" indicates the

grade. Only one grade is available. Larger quantity reels are available upon request.

Pin Descriptions

Pin Name Function

1 GND Power supply ground input.

2 OUT Negative voltage output.

3 CAP− Connect this pin to the negative terminal of the charge-pump capacitor.

4SD

Shutdown control pin, tie this pin to V+ in normal operation, and to GND for shutdown.

5 V+ Power supply positive voltage input.

6 CAP+ Connect this pin to the positive terminal of the charge-pump capacitor.

Circuit Description

The LM2664 contains four large CMOS switches which are

switched in a sequence to invert the input supply voltage.

Energy transfer and storage are provided by external capaci-

tors. Figure 2 illustrates the voltage conversion scheme.

When S

and S

are closed, C1charges to the supply

voltage V+. During this time interval, switches S

and S

are

open. In the second time interval, S

and S

are open; at the

same time, S

and S

are closed, C

is charging C

. After a

number of cycles, the voltage across C

will be pumped to

V+. Since the anode of C

is connected to ground, the output

at the cathode of C

equals −(V+) when there is no load

current. The output voltage drop when a load is added is

determined by the parasitic resistance (R

ds(on)

of the MOS-

FET switches and the ESR of the capacitors) and the charge

transfer loss between capacitors. Details will be discussed in

the following application information section.

10003105

FIGURE 2. Voltage Inverting Principle

LM2664

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Application Information

SIMPLE NEGATIVE VOLTAGE CONVERTER

The main application of LM2664 is to generate a negative

supply voltage. The voltage inverter circuit uses only two

external capacitors as shown in the Basic Application Cir-

cuits. The range of the input supply voltage is 1.8V 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 −(V+). The output resistance R

out

is a

function of the ON resistance of the internal MOSFET

switches, the oscillator frequency, the capacitance and ESR

of C

and C

. Since the switching current charging and

discharging C

is approximately twice as the output current,

the effect of the ESR of the pumping capacitor C

will be

multiplied by four in the output resistance. The output ca-

pacitor C

is charging and discharging at a current approxi-

mately equal to the output current, therefore, its ESR only

counts once in the output resistance. A good approximation

of R

out

is:

where R

is the sum of the ON resistance of the internal

MOSFET switches shown in Figure 2.

High capacitance, low ESR capacitors will reduce the output

resistance.

The peak-to-peak output voltage ripple is determined by the

oscillator frequency, the capacitance and ESR of the output

capacitor C

Again, using a low ESR capacitor will result in lower ripple.

SHUTDOWN MODE

A shutdown (SD ) pin is available to disable the device and

reduce the quiescent current to 1µA. Applying a voltage less

than 20% of V+ to the SD pin will bring the device into

shutdown mode. While in normal operating mode, the pin is

connected to V+.

CAPACITOR SELECTION

As discussed in the Simple Negative Voltage Converter

section, the output resistance and ripple voltage are depen-

dent 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

Where I

(V+) is the quiescent power loss of the IC device,

and I

out

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 I

out

), the output volt-

age ripple, and the converter efficiency. Low ESR capacitors

(Table 1) are recommended to maximize efficiency, reduce

the output voltage drop and voltage ripple.

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

LM2664

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Other Applications

PARALLELING DEVICES

Any number of LM2664s can be paralleled to reduce the

output resistance. Each device must have its own pumping

capacitor C

, while only one output capacitor C

out

is needed

as shown in Figure 3. The composite output resistance is:

CASCADING DEVICES

Cascading the LM2664s is an easy way to produce a greater

negative voltage (e.g. A two-stage cascade circuit is shown

in Figure 4).

If n is the integer representing the number of devices cas-

caded, the unloaded output voltage V

out

is (-nV

). The ef-

fective output resistance is equal to the weighted sum of

each individual device:

out

=nR

out_1

+ n/2 R

out_2

+...+R

out_n

Note that, the number of n is practically limited since the

increasing of n significantly reduces the efficiency, and in-

creases the output resistance and output voltage ripple.

COMBINED DOUBLER AND INVERTER

In Figure 5, the LM2664 is used to provide a positive voltage

doubler and a negative voltage converter. Note that the total

current drawn from the two outputs should not exceed 50

mA.

10003110

FIGURE 3. Lowering Output Resistance by Paralleling Devices

10003111

FIGURE 4. Increasing Output Voltage by Cascading Devices

LM2664

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Other Applications (Continued)

REGULATING V

OUT

It is possible to regulate the negative output of the LM2664

by use of a low dropout regulator (such as LP2980). The

whole converter is depicted in Figure 6. This converter can

give a regulated output from −1.8V to −5.5V by choosing the

proper resistor ratio:

out

ref

(1+R

)

where, V

ref

= 1.23V

Note that, the following conditions must be satisfied simulta-

neously for worst case design:

in_min

out_min

drop_max

(LP2980)

out_max

(LM2664)

in_max

out_max

drop_min

(LP2980)

out_min

(LM2664)

10003112

FIGURE 5. Combined Voltage Doubler and Inverter

10003124

FIGURE 6. Combining LM2664 with LP2980 to Make a Negative Adjustable Regulator

LM2664

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Physical Dimensions inches (millimeters) unless otherwise noted

6-Lead Small Outline Package (M6)

NS Package Number MA06A

For Order Numbers, refer to the table in the "Ordering Information" section of this document.

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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LM2664 Switched Capacitor Voltage Converter

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