Datasheet MAX660M, MAX660MX Datasheet (NSC)

MAX660
Switched Capacitor Voltage Converter

MAX660 Switched Capacitor Voltage Converter

November 1999

General Description

The MAX660 CMOS charge-pump voltage converter inverts
a positive voltage in the range of 1.5V to 5.5V to the corre­sponding 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 effi­ciency greater than 90%at most loads, the MAX660 pro­vides ideal performance for battery powered systems. The
MAX660 may also be used as a positive voltage doubler.

The oscillator frequency can be lowered byadding an exter­nal capacitor to the OSC pin. Also, the OSC pin may be used
to drive the MAX660 with an external clock.Afrequency con­trol (FC) pin selects the oscillator frequency of 10 kHz or 80
kHz.

Typical Application Circuits

Voltage Inverter

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Connection Diagram

Features

n Inverts or doubles input supply voltage
n Narrow SO-8 Package
n 6.5Ω typical output resistance
n 88%typical conversion efficiency at 100 mA
n Selectable oscillator frequency: 10 kHz/80 kHz

Applications

n Laptop computers
n Cellular phones
n Medical instruments
n Operational amplifier power supplies
n Interface power supplies
n Handheld instruments

Positive Voltage Doubler

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8-Lead SO

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Top View

Ordering Information

Order Number Top Mark Package Supplied as

MAX660M Date Code

MAX660M

MAX660MX Date Code

MAX660M

© 1999 National Semiconductor Corporation DS100898 www.national.com

M08A Rail (95 units/rail)

M08A Tape and Reel (2500 units/rail)

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

MAX660

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 The least negative of (OUT − 0.3V)

V+ and OUT Continuous Output Current 120 mA

or (V+ − 6V) to (V+ + 0.3V)

Power Dissipation

=

25˚C) (Note 3) 735 mW

(T

A

Max (Note 3) 150˚C

T

J

(Note 3) 170˚C/W

θ

JA

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

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

Electrical Characteristics

Limits in standard typeface are for T
less otherwise specified: V+=5V, FC=Open, C

Symbol Parameter Condition Min Typ Max Units

V+ Supply Voltage R

I

Q

I

L

R

OUT

F

OSC

I

OSC

P

EFF

V

OEFF

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 P
ambient temperature, and θ

Note 4: In the test circuit, capacitors C
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 be­low 3.5V, connect the LV pin to GND.

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

Supply Current No Load FC=Open 0.12 0.5

Output Current TA≤ +85˚C, OUT ≤ −4V 100

Output Resistance (Note 6) I

Oscillator Frequency OSC=Open FC=Open 5 10

OSC Input Current FC=Open

Power Efficiency RL(1k) between V+and OUT 96 98

Voltage Conversion Efficiency No Load 99 99.96

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

JA

=

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

J

=

=

C

150 µF. (Note 4)

1

2

=

1k Inverter, LV=Open

L

(Note 5)

3.5 5.5

Inverter, LV=GND 1.5 5.5 V
Doubler, LV=OUT 2.5 5.5

1 3

>

+85˚C, OUT ≤ −3.8V 100

T

A

=

100 mA T

L

≤ +85˚C 6.5 10

A

>

+85˚C 12

T

A

FC=V+ 40 80

±

2

±

FC=V+

R

(500Ω) between GND and OUT 92 96

L

=

I

100 mA to GND 88

L

=

DMax

and C2are 0.2Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output volt-

1

(T

JMax−TA

)/θJA, where T

is the maximum junction temperature, TAis the

JMax

16

mALV=Open FC=V+

mA

Ω

kHz

µA

%

%

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Test Circuit

FIGURE 1. MAX660 Test Circuit

Typical Performance Characteristics

(Circuit of

Figure 1

MAX660

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)

Supply Current vs
Supply Voltage

Output Source Resistance
vs Temperature

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Supply Current vs
Oscillator Frequency

Efficiency vs Load
Load Current

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Output Source Resistance
vs Supply Voltage

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Output Voltage Drop
vs Load Current

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Typical Performance Characteristics (Circuit of

MAX660

Efficiency vs
Oscillator Frequency

Output Voltage vs
Oscillator Frequency

Figure 1

) (Continued)

Oscillator Frequency
vs External Capacitance

Oscillator Frequency
Supply Voltage
(FC=V+)

Oscillator Frequency
vs Temperature
(FC=Open)

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Oscillator Frequency vs
Supply Voltage
(FC=Open)

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Oscillator Frequency vs
Temperature
(FC=V+)

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Pin Description

Pin Name Function

Voltage Inverter Voltage Doubler

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

FC=open, f
FC=V+, f
FC has no effect when OSC pin is driven externally.

2 CAP+ Connect this pin to the positive terminal of

charge-pump capacitor.
3 GND Power supply ground input. Power supply positive voltage input.
4 CAP− Connect this pin to the negative terminal of

charge-pump capacitor.
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.
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.
8 V+ Power supply positive voltage input. Positive voltage output.

OSC

OSC

=

10 kHz (typ);

=

80 kHz (typ);

Same as inverter.

Same as inverter.

LV must be tied to OUT.

Same as inverter except that OSC cannot be driven
by an external clock.

MAX660

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 capaci­tors.

Figure 2

When S
age V+. During this time interval switches S
open. In the second time interval, S
and S4are closed, C1is charging C2. After a number of
cycles, the voltage across C
the anode of C
cathode of C
in the switches, and no ESR in the capacitors. In reality, the
charge transfer efficiency depends on the switching fre­quency, the on-resistance of the switches, and the ESR of
the capacitors.

illustrates the voltage conversion scheme.

and S3are closed, C1charges to the supply volt-

1

and S3are open and S

1

will be pumped to V+. Since

is connected to ground, the output at the

2

equals −(V+) assuming no load on C2, no loss

2

2

and S4are

2

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FIGURE 2. Voltage Inverting Principle

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 ex­ternal capacitors as shown in the TypicalApplication 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

2

to ground to bypass the internal regulator circuitry. This gives
the best performance in low voltage applications. If the sup­ply voltage is greater than 3.5V, LV may be connected to
ground or left open. The choice of leaving LVopen 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 volt­age source equals −(V+). The output resistance R
function of the ON resistance of the internal MOS switches,
the oscillator frequency, and the capacitance and ESR of C
and C2. A good approximation is:

where RSWis the sum of the ON resistance of the internal
MOS switches shown in

High value, low ESR capacitors will reduce the output resis­tance. Instead of increasing the capacitance, the oscillator
frequency can be increased to reduce the 2/(f
Once this term is trivial compared with R
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

Figure 2

.

:

2

oscxC1

and ESRs, fur-

SW

out

) term.

is a

1

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Application Information (Continued)

MAX660

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

POSITIVE VOLTAGE DOUBLER

The MAX660 can operate as a positive voltage doubler (as
shown in the TypicalApplicationCircuits).The doubling func­tion is achieved by reversing some of the connections 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
ward drop.

The Schottky diode D
nal 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, D
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

1

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 MAX660 as a precision voltage di­vider. Since the off-voltage across each switch equals V
the input voltage can be raised to +11V.

CHANGING OSCILLATOR FREQUENCY

The internal oscillator frequency can be selected using the
Frequency Control (FC) pin. When FC is open, the oscillator
frequency is 10 kHz; when FC is connected to V+, the fre­quency increases to 80 kHz. A higher oscillator frequency al-

is only needed for start-up. The inter-

1

FIGURE 3. Splitting VINin Half

’s for-

1

IN

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lows smaller capacitors to be used for equivalent output re­sistance and ripple, but increases the typical supply current
from 0.12 mA to 1 mA.

The oscillator frequency can be lowered by adding an exter­nal capacitor between OSC and GND. (See Typical Perfor­mance Characteristics.) Also, in the inverter mode, an exter­nal 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. MAX660 Oscillator Frequency Selection

FC OSC Oscillator

Open Open 10 kHz
V+ Open 80 kHz
Open

is

1

or V+

N/A External Clock

External
Capacitor

(inverter mode only)

See Typical
Performance
Characteristics

External Clock
Frequency

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

/2,

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

2

and I

R

is the conversion loss associated with the

L

OUT

switch on-resistance, the two external capacitors and their
ESRs.

Since the switching current charging and discharging C
approximately twice as the output current, the effect of the
ESR of the pumping capacitor C
output resistance. The output capacitor C
discharging at a current approximately equal to the output

is multiplied by four in the

1

is charging and

2

is

1

current, therefore, its ESR only counts once in the output re­sistance. However, the ESR of C
voltage ripple. Therefore, low ESR capacitors (

directly affects the output

2

Table 2

) are
recommended for both capacitors to maximize efficiency,re­duce the output voltage drop and voltage ripple. For conve­nience, C

and C2are usually chosen to be the same.

1

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

Figure 4

, the output resistance vs. os­cillator frequency curves are drawn for three different tanta­lum capacitors. 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 20 kHz for the 150 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. For lower ESR, use
ceramic capacitors.

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Application Information (Continued)

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FIGURE 4. Output Source Resistance vs Oscillator Frequency

TABLE 2. Low ESR Capacitor Manufacturers

Manufacturer Phone FAX Capacitor Type

Nichicon Corp. (708)-843-7500 (708)-843-2798 PL, PF series, through-hole aluminum electrolytic
AVX Corp. (803)-448-9411 (803)-448-1943 TPS series, surface-mount tantalum
Sprague (207)-324-4140 (207)-324-7223 593D, 594D, 595D series, surface-mount tantalum
Sanyo (619)-661-6835 (619)-661-1055 OS-CON series, through-hole aluminum electrolytic

MAX660

Other Applications

PARALLELING DEVICES

Any number of MAX660s can be paralleled to reduce the output resistance. Each device must have its own pumping capacitor
C

, while only one output capacitor C

1

FIGURE 5. Lowering Output Resistance by Paralleling Devices

CASCADING DEVICES

Cascading the is an easy way to produce a greater negative voltage (as shown in
number of devices cascaded, the unloaded output voltage V
sum of each individual device:

is needed as shown in

out

Figure 5

. The composite output resistance is:

DS100898-7

Figure 6

is (−nVin). The effective output resistance is equal to the weighted

out

). If n is the integer representing the

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Other Applications (Continued)

A three-stage cascade circuit shown in

MAX660

Cascading is also possible when devices are operating in doubling mode. In
An example of using the circuit in
Note that the number of n is practically limited since the increasing of n significantly reduces the efficiency and increases the out-

put resistance and output voltage ripple.

Figure 7

generates −3Vin, from Vin.

Figure 8

, two devices are cascaded to generate 3Vin.

Figure 7orFigure 8

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

FIGURE 6. Increasing Output Voltage by Cascading Devices

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REGULATING V

FIGURE 7. Generating −3Vinfrom +V

FIGURE 8. Generating +3Vinfrom +V

out

in

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in

It is possible to regulate the output of the MAX660 by use of a low dropout regulator (such as LP2951). The whole converter is
depicted in

where

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V

ref

Figure 9

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

=

1.235V.

Other Applications (Continued)

The error flag on pin 5 of the LP2951 goes low when the regulated output at pin 4 drops by about 5%. The LP2951 can be shut­down by taking pin 3 high.

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FIGURE 9. Combining MAX660 with LP2951 to Make a Negative Adjustable Regulator

Also, as shown in

Figure 10

the output, we can get +5V output from an input as low as +3V.

by operating MAX660 in voltage doubling mode and adding a linear regulator (such as LP2981) at

MAX660

FIGURE 10. Generating +5V from +3V Input Voltage

DS100898-12

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Other Applications (Continued)

OTHER SWITCHED-CAPACITOR CONVERTERS

MAX660

Please refer to

Package SOT23-6 SOT23-6 Mini SO-8 Mini SO-8 SO-8
Supply Current (typ., mA) 0.22 0.22 3.75 1.1 0.12 at 10kHz,

Output Ω (typ.) 12 12 4.2 4.2 6.5
Oscillator (kHz) 80 80 800 200 10, 80
Input (V) 1.8 to 5.5 1.8 to 5.5 2.5 to 6.25 2.5 to 6.25 1.8 to 5.5
Output Mode(s) Invert Double 3/2, 2/3 3/2, 2/3 Invert, Double

Package Mini SO-8, SO-8 Mini SO-8, SO-8 SO-8 SO-8
Supply Current (typ., mA) 0.12 at 10kHz,

Output Ω (typ.) 6.5 6.5 3.5 3.5
Oscillator (kHz) 10, 80 80 10, 70 70
Input (V) 1.8 to 5.5 1.8 to 5.5 1.8 to 5.5 1.8 to 5.5
Output Mode(s) Invert, Double Invert, Double Invert, Double Invert, Double

Table 3

, which shows National’s Switched-Capacitor Converter products.

TABLE 3. Switched-Capacitor Converters

LM2664 LM2665 LM3350 LM3351 MAX660

LM2660 LM2661 LM2662 LM2663

1.0 at 80kHz

1.0 0.3 at 10kHz,

1.0 at 80kHz

1.3

1.3 at 70kHz

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Physical Dimensions inches (millimeters) unless otherwise noted

8-Lead SO (M)

Order Number MAX660M

NS Package Number M08A

MAX660 Switched Capacitor Voltage Converter

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