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 cor-
responding negative voltage of -1.8V to -5.5V. The LM2664
uses two low cost capacitors to provide up to 40 mA of out-
put current.

The LM2664 operates at 160 kHz oscillator frequency to re-
duce output resistance and voltage ripple. With an operating
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

Inverts Input Supply Voltage

SOT23-6 Package

Typical Output Impedance

91% Typical Conversion Efficiency at 40 mA

1µA Typical Shutdown Current

Applications

Cellular Phones

Pagers

PDAs

Operational Amplifier Power Suppliers

Interface Power Suppliers

Handheld Instruments

Basic Application Circuits

Voltage Inverter

DS100031-1

+5V to -10V Converter

DS100031-25

November 1999

LM2664

Switched

Capacitor

oltage

Converter

DS100031

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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.

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

5.8V

(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

= C

= 3.3 µF. (Note 4)

Symbol

Parameter

Condition

Min

Typ

Max

Units

V+

Supply Voltage

1.8

5.5

Supply Current

No Load

220

500

µA

Shutdown Supply Current

µA

Shutdown Pin Input Voltage

Normal Operation

2.0

(Note 5)

Shutdown Mode

0.8

(Note 6)

Output Current

Sum of the R

ds(on)

of the four

internal MOSFET switches

= 40 mA

OUT

Output Resistance (Note 7)

= 40 mA

OSC

Oscillator Frequency

(Note 8)

160

kHz

Switching Frequency

(Note 8)

kHz

EFF

Power Efficiency

(1.0k) between GND and

OUT

= 40 mA to GND

OEFF

Voltage Conversion Efficiency

No Load

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 tem-
peratures 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

DMax

= (T

JMax

- T

, where T

JMax

is the maximum junction temperature, T

is the

ambient temperature, and

is the junction-to-ambient thermal resistance of the specified package.

Note 4: In the test circuit, capacitors C

and C

are 3.3 µF, 0.3

maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output

voltage and efficiency.

Note 5: The minimum input high for the shutdown pin equals 40% of V+.

Note 6: The maximum input low for the shutdown pin equals 20% of V+.

Note 7: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for simple negative voltage
converter.

Note 8: The output switches operate at one half of the oscillator frequency, f

OSC

= 2f

LM2664

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Connection Diagram

Ordering Information

Order Number

Package

Number

Package

Marking

Supplied as

LM2664M6

MA06A

SO3A (Note 9)

Tape and Reel (1000 units/rail)

LM2664M6X

MA06A

SO3A (Note 9)

Tape and Reel (3000 units/rail)

Note 9: The first letter

identifies the part as a switched capacitor converter. The next two numbers are the device number. The fourth letter

indicates the

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

Pin Description

Pin

Name

Function

GND

Power supply ground input.

OUT

Negative voltage output.

CAP-

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

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

V+

Power supply positive voltage input.

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, C

charges to the supply volt-

age 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 cur-

rent. The output voltage drop when a load is added is deter-
mined by the parasitic resistance (R

ds(on)

of the MOSFET

switches and the ESR of the capacitors) and the charge
transfer loss between capacitors. Details will be discussed in
the following application information section.

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 ex-
ternal capacitors as shown in the Basic Application Circuits.
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 dis-

charging C

is approximately twice as the output current, the

6-Lead Small Outline Package (M6)

DS100031-4

Top View With Package Marking

DS100031-22

Actual Size

DS100031-5

FIGURE 2. Voltage Inverting Principle

LM2664

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Application Information

(Continued)

effect of the ESR of the pumping capacitor C

will be multi-

plied by four in the output resistance. The output capacitor
C

is 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 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 shut-
down mode. While in normal operating mode, the pin is con-
nected to V+.

Capacitor Selection

As discussed in the

Simple Negative Voltage Converter sec-

tion, the output resistance and ripple voltage are dependent
on the capacitance and ESR values of the external capaci-
tors. 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

Other Applications

Paralleling Devices

Any number of LM2664s can be paralleled to reduce the out-
put resistance. Each device must have its own pumping ca-
pacitor C

, while only one output capacitor C

out

is needed as

shown in Figure 3. The composite output resistance is:

LM2664

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Other Applications

(Continued)

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 effec-

tive 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 in-
creasing 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.

DS100031-10

FIGURE 3. Lowering Output Resistance by Paralleling Devices

DS100031-11

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

= V

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)

+ I

out_max

x R

out_max

(LM2664)

in_max

out_max

drop_min

(LP2980)

+ I

out_min

x R

out_min

(LM2664)

DS100031-12

FIGURE 5. Combined Voltage Doubler and Inverter

DS100031-24

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

LM2664

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Physical Dimensions

inches (millimeters) unless otherwise noted

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www.national.com

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.

LM2664

Switched

Capacitor

oltage

Converter

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.

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