LM2662MDC - National Semiconductor

LM2662/LM2663

Switched Capacitor Voltage Converter

General Description

The LM2662/LM2663 CMOS charge-pump voltage con-

verter inverts a positive voltage in the range of 1.5V to 5.5V

to the corresponding negative voltage. The LM2662/LM2663

uses two low cost capacitors to provide 200 mA of output

current without the cost, size, and EMI related to inductor

based converters. With an operating current of only 300 µA

and operating efficiency greater than 90% at most loads, the

LM2662/LM2663 provides ideal performance for battery

powered systems. The LM2662/LM2663 may also be used

as a positive voltage doubler.

The oscillator frequency can be lowered by adding an exter-

nal capacitor to the OSC pin.Also, the OSC pin may be used

to drive the LM2662/LM2663 with an external clock. For

LM2662, a frequency control (FC) pin selects the oscillator

frequency of 20 kHz or 150 kHz. For LM2663, an external

shutdown (SD) pin replaces the FC pin. The SD pin can be

used to disable the device and reduce the quiescent current

to 10 µA. The oscillator frequency for LM2663 is 150 kHz.

Features

nInverts or doubles input supply voltage

nNarrow SO-8 Package

n3.5Ωtypical output resistance

n86% typical conversion efficiency at 200 mA

n(LM2662) selectable oscillator

frequency: 20 kHz/150 kHz

n(LM2663) low current shutdown mode

Applications

nLaptop computers

nCellular phones

nMedical instruments

nOperational amplifier power supplies

nInterface power supplies

nHandheld instruments

Basic Application Circuits

Voltage Inverter

DS100003-1

Positive Voltage Doubler

DS100003-2

Splitting V

in Half

DS100003-3

January 1999

LM2662/LM2663 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) 6V

LV (OUT − 0.3V) to (GND + 3V)

FC, OSC, SD The least negative of (OUT − 0.3V)

or (V+ − 6V) to (V+ + 0.3V)

V+ and OUT Continuous Output Current 250 mA

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

Power Dissipation (T

= 25˚C) (Note 3) 735 mW

Max (Note 3) 150˚C

(Note 3) 170˚C/W

Operating Junction Temperature

Range −40˚C to +85˚C

Storage Temperature Range −65˚C to +150˚C

Lead Temperature (Soldering, 10 seconds) 300˚C

ESD Rating 2 kV

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, FC = Open, C

= 47 µF.(Note 4)

Symbol Parameter Condition Min Typ Max Units

V+ Supply Voltage R

= 1k Inverter, LV = Open 3.5 5.5

Inverter, LV = GND 1.5 5.5 V

Doubler, LV = OUT 2.5 5.5

Supply Current No Load FC = V+ (LM2662) 1.3 4mALV = Open SD = Ground (LM2663)

FC = Open 0.3 0.8

Shutdown Supply Current 10 µA

(LM2663)

Shutdown Pin Input Voltage Shutdown Mode 2.0 (Note 5) V

(LM2663) Normal Operation 0.3

Output Current 200 mA

OUT

Output Resistance (Note 6) I

= 200 mA 3.5 7Ω

OSC

Oscillator Frequency (Note 7) OSC = Open FC = Open 720 kHz

FC=V+ 55 150

Switching Frequency (Note 8) OSC = Open FC = Open 3.5 10 kHz

FC=V+ 27.5 75

OSC

OSC Input Current FC = Open ±2µA

FC=V+ ±

EFF

Power Efficiency R

(500) between V

and OUT 90 96 %

= 200 mA to GND 86

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

)/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 47 µF, 0.2Ωmaximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce

output voltage and efficiency.

Note 5: In doubling mode, when Vout >5V, minimum input high for shutdown equals Vout −3V.

Note 6: Specified output resistance includes internal switch resistance and capacitor ESR.

Note 7: For LM2663, the oscillator frequency is 150 kHz.

Note 8: The output switches operate at one half of the oscillator frequency, fOSC =2f

SW.

LM2662/LM2663

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Test Circuits

Typical Performance Characteristics (Circuit of

Figure 1

)

DS100003-4

DS100003-5

FIGURE 1. LM2662 and LM2663 Test Circuits

Supply Current vs

Supply Voltage

DS100003-37

Supply Current vs

Oscillator Frequency

DS100003-38

Output Source

Resistance vs Supply

Voltage

DS100003-39

LM2662/LM2663

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Typical Performance Characteristics (Circuit of

Figure 1

) (Continued)

Output Source

Resistance vs

Temperature

DS100003-40

Output Source

Resistance vs

Temperature

DS100003-41

Efficiency vs Load

Current

DS100003-42

Output Voltage Drop

vs Load Current

DS100003-43

Efficiency vs

Oscillator Frequency

DS100003-44

Output Voltage vs

Oscillator Frequency

DS100003-45

LM2662/LM2663

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Typical Performance Characteristics (Circuit of

Figure 1

) (Continued)

Oscillator Frequency

vs External

Capacitance

DS100003-46

Oscillator Frequency

vs Supply Voltage

DS100003-47

Oscillator Frequency

vs Supply Voltage

DS100003-48

Oscillator Frequency

vs Temperature

DS100003-49

Oscillator Frequency

vs Temperature

DS100003-50

Shutdown Supply

Current vs

Temperature

(LM2663 Only)

DS100003-51

LM2662/LM2663

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Connection Diagrams

Pin Description

Pin Name Function

Voltage Inverter Voltage Doubler

1 FC Frequency control for internal oscillator: Same as inverter.

(LM2662) FC = open, f

OSC

= 20 kHz (typ);

FC = V+, f

OSC

= 150 kHz (typ);

FC has no effect when OSC pin is driven

externally.

1SD

(LM2663) Shutdown control pin, tie this pin to the ground

in normal operation. Same as inverter.

2 CAP+ Connect this pin to the positive terminal of

charge-pump capacitor. Same as inverter.

3 GND Power supply ground input. Power supply positive voltage input.

4 CAP− Connect this pin to the negative terminal of

charge-pump capacitor. Same as inverter.

5 OUT Negative voltage output. Power supply ground input.

6 LV Low-voltage operation input. Tie LV to GND

when input voltage is less than 3.5V. Above

3.5V, LV can be connected to GND or left

open. When driving OSC with an external clock,

LV must be connected to GND.

LV must be tied to OUT.

7 OSC Oscillator control input. OSC is connected to an

internal 15 pF capacitor. An external capacitor

can be connected to slow the oscillator. Also,

an external clock can be used to drive OSC.

Same as inverter except that OSC cannot be

driven by an external clock.

8 V+ Power supply positive voltage input. Positive voltage output.

Circuit Description

The LM2662/LM2663 contains four large CMOS switches

which are switched in a sequence to invert the input supply

voltage. Energy transfer and storage are provided by exter-

nal capacitors.

Figure 2

illustrates the voltage conversion

scheme. When S

and S

are closed, C

charges to the

supply voltage V+. During this time interval switches S

and

are open. In the second time interval, S

and S

are open

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+) assuming no load on C

, no loss

in the switches, and no ESR in the capacitors. In reality, the

charge transfer efficiency depends on the switching fre-

quency, the on-resistance of the switches, and the ESR of

the capacitors.

8-Lead SO (M)

DS100003-20 DS100003-21

Top View

Order Number LM2662M, LM2663M

See NS Package Number M08A

DS100003-22

FIGURE 2. Voltage Inverting Principle

LM2662/LM2663

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Application Information

SIMPLE NEGATIVE VOLTAGE CONVERTER

The main application of LM2662/LM2663 is to generate a

negative supply voltage. The voltage inverter circuit uses

only two external capacitors as shown in the Basic Applica-

tion Circuits. The range of the input supply voltage is 1.5V to

5.5V. For a supply voltage less than 3.5V, the LV pin must be

connected to ground to bypass the internal regulator cir-

cuitry. This gives the best performance in low voltage appli-

cations. If the supply voltage is greater than 3.5V, LV may be

connected to ground or left open. The choice of leaving LV

open simplifies the direct substitution of the LM2662/

LM2663 for the LMC7660 Switched Capacitor Voltage Con-

verter.

The output characteristics of this circuit can be approximated

by an ideal voltage source in series with a resistor. The

voltage source equals −(V+). The output resistance R

out

is a

function of the ON resistance of the internal MOS switches,

the oscillator frequency, and the capacitance and ESR of C

and C

. Since the switching current charging and discharg-

ing C

is approximately twice as the output current, the effect

of the ESR of the pumping capacitor C

is multiplied 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 is:

where R

is the sum of the ON resistance of the internal

MOS switches shown in

Figure 2

High value, low ESR capacitors will reduce the output resis-

tance. Instead of increasing the capacitance, the oscillator

frequency can be increased to reduce the 2/(f

osc

) term.

Once this term is trivial compared with R

and ESRs,

further increasing in oscillator frequency and capacitance will

become ineffective.

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

oscillator frequency, and the capacitance and ESR of the

output capacitor C

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

POSITIVE VOLTAGE DOUBLER

The LM2662/LM2663 can operate as a positive voltage dou-

bler (as shown in the Basic Application Circuits). The dou-

bling function is achieved by reversing some of the connec-

tions to the device. The input voltage is applied to the GND

pin with an allowable voltage from 2.5V to 5.5V. The V+ pin

is used as the output. The LV pin and OUT pin must be

connected to ground. The OSC pin can not be driven by an

external clock in this operation mode. The unloaded output

voltage is twice of the input voltage and is not reduced by the

diode D

’s forward drop.

The Schottky diode D

is only needed for start-up. The

internal oscillator circuit uses the V+ pin and the LV pin

(connected to ground in the voltage doubler circuit) as its

power rails. Voltage across V+ and LV must be larger than

1.5V to insure the operation of the oscillator. During start-up,

is used to charge up the voltage at V+ 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 D

should 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 Applica-

tion Circuits is using the LM2662/LM2663 as a precision

voltage divider. Since the off-voltage across each switch

equals V

/2, the input voltage can be raised to +11V.

CHANGING OSCILLATOR FREQUENCY

For the LM2662, the internal oscillator frequency can be

selected using the Frequency Control (FC) pin. When FC is

open, the oscillator frequency is 20 kHz; when FC is con-

nected to V+, the frequency increases to 150 kHz. A higher

oscillator frequency allows smaller capacitors to be used for

equivalent output resistance and ripple, but increases the

typical supply current from 0.3 mA to 1.3 mA.

The oscillator frequency can be lowered by adding an exter-

nal capacitor between OSC and GND (See typical perfor-

mance characteristics). Also, in the inverter mode, an exter-

nal clock that swings within 100 mV of V+ and GND can be

used to drive OSC. Any CMOS logic gate is suitable for

driving OSC. LV must be grounded when driving OSC. The

maximum external clock frequency is limited to 150 kHz.

The switching frequency of the converter (also called the

charge pump frequency) is half of the oscillator frequency.

Note: OSC cannot be driven by an external clock in the voltage-doubling

mode.

TABLE 1. LM2662 Oscillator Frequency Selection

FC OSC Oscillator

Open Open 20 kHz

V+ Open 150 kHz

Open or V+ External Capacitor See Typical

Performance

Characteristics

N/A External Clock External Clock

(inverter mode only) Frequency

TABLE 2. LM2663 Oscillator Frequency Selection

OSC Oscillator

Open 150 kHz

External

Capacitor See Typical Performance

Characteristics

External Clock External Clock Frequency

(inverter mode only)

SHUTDOWN MODE

For the LM2663, a shutdown (SD) pin is available to disable

the device and reduce the quiescent current to 10 µA. Ap-

plying a voltage greater than 2V to the SD pin will bring the

device into shutdown mode. While in normal operating

mode, the SD pin is connected to ground.

LM2662/LM2663

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Application Information (Continued)

CAPACITOR SELECTION

As discussed in the

Simple Negative Voltage Converter

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

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.

Low ESR capacitors (

Table 3

) are recommended for both capacitors to maximize efficiency, reduce the output voltage drop and

voltage ripple. For convenience, C

and C

are usually chosen to be the same.

The output resistance varies with the oscillator frequency and the capacitors. In

Figure 3

, the output resistance vs. oscillator

frequency curves are drawn for four difference capacitor values. At very low frequency range, capacitance plays the most

important role in determining the output resistance. Once the frequency is increased to some point (such as 100 kHz for the 47

µF capacitors), the output resistance is dominated by the ON resistance of the internal switches and the ESRs of the external

capacitors. A low value, smaller size capacitor usually has a higher ESR compared with a bigger size capacitor of the same type.

Ceramic capacitors can be chosen for their lower ESR. As shown in

Figure 3

, in higher frequency range, the output resistance

using the 10 µF ceramic capacitors is close to these using higher value tantalum capacitors.

TABLE 3. 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

DS100003-36

FIGURE 3. Output Source Resistance vs Oscillator Frequency

LM2662/LM2663

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Other Applications

PARALLELING DEVICES

Any number of LM2662s (or LM2663s) 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 4

. The composite output resistance is:

CASCADING DEVICES

Cascading the LM2662s (or LM2663s) is an easy way to produce a greater negative voltage (as shown in

Figure 5

). If n is the

integer representing the number of devices cascaded, the unloaded output voltage V

out

is (−nV

). The effective output resistance

is equal to the weighted sum of each individual device:

A three-stage cascade circuit shown in

Figure 6

generates −3V

, from V

Cascading is also possible when devices are operating in doubling mode. In

Figure 7

, two devices are cascaded to generate 3V

An example of using the circuit in

Figure 6

Figure 7

is generating +15V or −15V from a +5V input.

Note that, the number of n is practically limited since the increasing of n significantly reduces the efficiency and increases the

output resistance and output voltage ripple.

DS100003-24

FIGURE 4. Lowering Output Resistance by Paralleling Devices

DS100003-25

FIGURE 5. Increasing Output Voltage by Cascading Devices

LM2662/LM2663

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Other Applications (Continued)

REGULATING V

out

It is possible to regulate the output of the LM2662/LM2663 by use of a low dropout regulator (such as LP2986). The whole

converter is depicted in

Figure 8

. This converter can give a regulated output from −1.5V to −5.5V by choosing the proper resistor

ratio:

where, V

ref

= 1.23

The error flag on pin 7 of the LP2986 goes low when the regulated output at pin 5 drops by about 5% below nominal. The LP2986

can be shutdown by taking pin 8 low. The less than 1 µAquiescent current in the shutdown mode is favorable for battery powered

applications.

DS100003-26

FIGURE 6. Generating −3V

from +V

DS100003-27

FIGURE 7. Generating +3V

from +V

DS100003-28

FIGURE 8. Combining LM2662/LM2663 with LP2986 to Make a Negative Adjustable Regulator

LM2662/LM2663

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Other Applications (Continued)

Also, as shown in

Figure 9

by operating the LM2662/LM2663 in voltage doubling mode and adding a low dropout regulator (such

as LP2986) at the output, we can get +5V output from an input as low as +3.3V.

DS100003-29

FIGURE 9. Generating +5V from +3.3V Input Voltage

LM2662/LM2663

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Physical Dimensions inches (millimeters) unless otherwise noted

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www.national.com

8-Lead SO (M)

Order Number LM2662M or LM2663M

NS Package Number M08A

LM2662/LM2663 Switched Capacitor Voltage 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.