MAX660
Switched Capacitor Voltage Converter

General Description

The MAX660 CMOS charge-pump voltage converter inverts
a positive voltage in the range of 1.5V to 5.5V to the corre-
sponding negative voltage. The MAX660 uses two low cost
capacitors to provide 100 mA of output current without the
cost, size, and EMI related to inductor based converters.
With an operating current of only 120 µA and operating effi-
ciency greater than 90% at most loads, the MAX660 pro-
vides ideal performance for battery powered systems. The
MAX660 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 MAX660 with an external clock. A frequency con-
trol (FC) pin selects the oscillator frequency of 10 kHz or 80
kHz.

Features

Inverts or doubles input supply voltage

Narrow SO-8 Package

6.5

typical output resistance

88% typical conversion efficiency at 100 mA

Selectable oscillator frequency: 10 kHz/80 kHz

Applications

Laptop computers

Cellular phones

Medical instruments

Operational amplifier power supplies

Interface power supplies

Handheld instruments

Typical Application Circuits

Connection Diagram

Ordering Information

Order Number

Top Mark

Package

Supplied as

MAX660M

Date Code

MAX660M

M08A

Rail (95 units/rail)

MAX660MX

Date Code

MAX660M

M08A

Tape and Reel (2500 units/rail)

Voltage Inverter

DS100898-1

Positive Voltage Doubler

DS100898-2

8-Lead SO

DS100898-5

Top View

November 1999

MAX660

Switched

Capacitor

oltage

Converter

DS100898

www.national.com

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)

(OUT - 0.3V) to (GND + 3V)

FC, OSC

The least negative of (OUT - 0.3V)

or (V+ - 6V) to (V+ + 0.3V)

V+ and OUT Continuous Output Current

120 mA

Output Short-Circuit Duration to GND (Note 2)

1 sec.

Power Dissipation

= 25°C) (Note 3)

735 mW

Max (Note 3)

150°C

(Note 3)

170°C/W

Operating Junction Temp. Range

-40°C to +85°C

Storage Temperature Range

-65°C to +150°C

Lead Temperature

300°C

(Soldering, 10 seconds)

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

= C

= 150 µF. (Note 4)

Symbol

Parameter

Condition

Min

Typ

Max

Units

V+

Supply Voltage

= 1k

Inverter, LV = Open
(Note 5)

3.5

5.5

Inverter, LV = GND

1.5

5.5

Doubler, LV = OUT

2.5

5.5

Supply Current

No Load

FC = Open

0.12

0.5

LV = Open

FC = V+

Output Current

+85°C, OUT

-4V

100

+85°C, OUT

-3.8V

100

OUT

Output Resistance (Note 6)

= 100 mA

+85°C

6.5

+85°C

OSC

Oscillator Frequency

OSC = Open

FC = Open

kHz

FC = V+

OSC

OSC Input Current

FC = Open

µA

FC = V+

EFF

Power Efficiency

(1k) between V

and OUT

(500

) between GND and OUT

= 100 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 0.2

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

age and efficiency.

Note 5: The minimum limit for this parameter is different from the limit of 3.0V for the industry-standard "660" product. For inverter operation with supply voltage be-
low 3.5V, connect the LV pin to GND.

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

MAX660

www.national.com

Pin Description

Pin

Name

Function

Voltage Inverter

Voltage Doubler

Frequency control for internal oscillator:

Same as inverter.

FC = open, f

OSC

= 10 kHz (typ);

FC = V+, f

OSC

= 80 kHz (typ);

FC has no effect when OSC pin is driven externally.

CAP+

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

Same as inverter.

GND

Power supply ground input.

Power supply positive voltage input.

CAP-

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

Same as inverter.

OUT

Negative voltage output.

Power supply ground input.

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.

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.

V+

Power supply positive voltage input.

Positive voltage output.

Circuit Description

The MAX660 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 and 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+) 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.

Application Information

SIMPLE NEGATIVE VOLTAGE CONVERTER

The main application of MAX660 is to generate a negative
supply voltage. The voltage inverter circuit uses only two ex-
ternal capacitors as shown in the Typical Application 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 circuitry. This gives
the best performance in low voltage applications. If the sup-
ply 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 MAX660 for the LMC7660
Switched Capacitor Voltage Converter.

The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistor. The volt-
age 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

. 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

x C

) term.

Once this term is trivial compared with R

and ESRs, fur-

ther 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

DS100898-21

FIGURE 2. Voltage Inverting Principle

MAX660

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