MAX860, MAX861

19-0239; Rev 2; 4/03

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

_______________General Description

The MAX860/MAX861 charge-pump voltage converters invert input voltages ranging from +1.5V to +5.5V, or double input voltages ranging from +2.5V to +5.5V.

Because of their high switching frequencies, these devices use only two small, low-cost capacitors. Their

50mA output makes switching regulators unnecessary, eliminating inductors and their associated cost, size, and EMI. Greater than 90% efficiency over most of the load-current range, combined with a typical operating current of only 200µA (MAX860), provides ideal performance for both battery-powered and board-level voltage-conversion applications.

A frequency-control (FC) pin provides three switchingfrequencies to optimize capacitor size and quiescent current and to prevent interference with sensitive cir-

— frequencies. A shutdown (S

—

H

—

D

–

N ) pin reduces current consumption to less than 1µA. The MAX860/MAX861 are suitable for use in applications where the ICL7660 and MAX660's switching frequencies are too low. The

MAX860/MAX861 are available in 8-pin µMAX and

SO packages.

________________________Applications

Portable Computers

Medical Instruments

Interface Power Supplies

Hand-Held Instruments

Operational-Amplifier Power Supplies

__________Typical Operating Circuit

____________________________Features

♦ 8-Pin, 1.11mm High µMAX Package

♦ Invert or Double the Input Supply Voltage

♦ Three Selectable Switching Frequencies

♦ High Frequency Reduces Capacitor Size

♦ 87% Efficiency at 50mA

♦ 200µA Quiescent Current (MAX860)

♦ 1µA Shutdown Supply Current

♦ 600mV Voltage Drop at 50mA Load

♦ 12Ω Output Resistance

______________Ordering Information

PART

MAX860ISA

MAX860IUA

MAX860C/D

MAX860ESA

MAX860MJA

MAX861ISA

MAX861IUA

MAX861C/D

MAX861ESA

MAX861MJA

TEMP RANGE

-25°C to +85°C

-25°C to +85°C

0°C to +70°C

-40°C to +85°C

-55°C to +125°C

-25°C to +85°C

-25°C to +85°C

0°C to +70°C

-40°C to +85°C

-55°C to +125°C

*Dice are tested at T

A

= +25°C, DC parameters only.

†Contact factory for availability.

PIN-PACKAGE

8 SO

8 µMAX

Dice*

8 SO

8 CERDIP†

8 SO

8 µMAX

Dice*

8 SO

8 CERDIP†

C1

1

2

FC

C1+

MAX860

MAX861

V

DD

SHDN

3

GND

10

µF

4

C1-

LV

OUT

8

7

6

5

INPUT

VOLTAGE

+1.5V TO +5.5V

INVERTED

NEGATIVE

OUTPUT

10

µF

C2

__________________Pin Configuration

TOP VIEW

VOLTAGE INVERTER

INPUT

VOLTAGE

+2.5V TO +5.5V

C1

1

2

FC

C1+

MAX860

MAX861

V

DD

SHDN

3

GND

10

µF

4

C1-

LV

OUT

8

7

6

5

POSITIVE VOLTAGE DOUBLER

DOUBLED

POSITIVE

OUTPUT

C2

10

µF

FC

1

C1+ 2

GND

3

C1-

4

MAX860

MAX861

SO/

µMAX

7

6

8

V

DD

SHDN

LV

5

OUT

________________________________________________________________ Maxim Integrated Products 1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (V

DD

Input Voltage Range (LV, FC,

—

S

—

H

—

D

–

N ) ...................(OUT - 0.3V) to (V

DD

+ 0.3V)

Continuous Output Current (OUT, V

DD

) .............................60mA

Output Short-Circuit to GND (Note 1).......................................1s

Continuous Power Dissipation (T

A

= +70°C)

SO (derate 5.88mW/°C above +70°C) .........................471mW

µMAX (derate 4.10mW/°C above +70°C) ....................330mW

CERDIP (derate 8.00mW/°C above +70°C) .................640mW

Operating Temperature Ranges

MAX86_I_A ......................................................-25°C to +85°C

MAX86_ESA.....................................................-40°C to +85°C

MAX86_MJA ..................................................-55°C to +125°C

Storage Temperature Range .............................-65°C to +160°C

Lead Temperature (soldering, 10s) .................................+300°C

Note 1:

OUT may be shorted to GND for 1sec without damage, but shorting OUT to V

DD may damage the device and should be avoided. Also, for temperatures above +85°C, OUT must not be shorted to GND or V

DD

, even instantaneously, or device damage may result.

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(Typical Operating Circuit (Inverter), V

DD

= +5V,

– —

S

—

H otherwise noted. Typical values are at T

A

= +25°C.)

—

D

–

N = V

DD

, FC = LV = GND, C1 = C2 = 10µF (Note 2), T

A

= T

MIN to T

MAX

, unless

PARAMETER SYMBOL TYP UNITS

Supply Voltage

No-Load Supply Current

(Note 3)

V

DD

I

DD

R

L

= 1k

Ω

MAX860I/E

MAX860M

MAX861I/E

MAX861M

CONDITIONS

Inverter, LV = GND

Doubler, LV = OUT

FC = V

DD

= 5V

FC = V

DD

= 3V

FC = GND

FC = OUT

FC = V

DD

FC = GND

FC = OUT

FC = V

DD

FC = GND

FC = OUT

FC = V

DD

FC = GND

FC = OUT

MIN

1.5

2.5

0.2

0.07

0.6

1.4

0.3

1.1

2.5

MAX

5.5

5.5

0.3

3.3

0.4

2.0

5.0

0.5

2.6

6.5

1.0

2.5

0.4

1.3

V mA

V

DD

= 5V, V

OUT more negative than -3.75V

50 100

Output Current I

OUT mA

Output Resistance

(Note 4)

R

OUT

V

DD

= 3V, V

OUT more negative than -2.5V

I

L

= 50mA

I

L

= 10mA, V

DD

= 2V

10 30

12

20

25

35

Ω

2 _______________________________________________________________________________________

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

ELECTRICAL CHARACTERISTICS (continued)

(Typical Operating Circuit (Inverter), V

DD

= +5V,

– — —

= V

DD

, FC = LV = GND, C1 = C2 = 10µF (Note 2), T

A

= T

MIN to T

MAX

, unless otherwise noted. Typical values are at T

A

= +25°C.)

PARAMETER SYMBOL MAX UNITS

Switching Frequency

(Note 5)

FC Current (from V

DD

) f

S

I

FC

MAX860

MAX861

FC < 4V

CONDITIONS

FC = V

DD

FC = GND

FC = OUT

FC = V

DD

FC = GND

FC = OUT

MIN

3

30

80

8

60

160

TYP

6

50

130

13

100

250

-2 -4 kHz

µA

Power Efficiency (Note 6)

MAX860,

FC = V

DD

MAX861,

FC = V

DD

R

L

= 2k

Ω from V

DD to OUT

R

L

= 1k

Ω from OUT to GND

R

L

= 2k

Ω from V

DD to OUT

R

L

= 1k

Ω from OUT to GND

93

90

93

88

96

93

96

92

%

MAX860/MAX861, FC = V

DD

,

I

L

= 50mA to GND, C1 = C2 = 68µF

87

Voltage-Conversion Efficiency No load 99 99.9

%

–

S H

—

D

— –

N Threshold

V

IH

V

IL

LV = GND

–

S

—

H

—

D

— –

N < 0.3V

1.2

V

Shutdown Supply Current

MAX86_I/E

MAX86_M

0.3

1

10

µA

Time to Exit Shutdown No load, V

OUT

= -4V 500 µs

Note 2:

C1 and C2 are low-ESR (<0.2

Ω) aluminum electrolytics. Capacitor ESR adds to the circuit’s output resistance. Using capacitors with higher ESR may reduce output voltage and efficiency.

Note 3:

MAX860/MAX861 may draw high supply current during startup, up to the minimum operating supply voltage. To guarantee proper startup, the input supply must be capable of delivering 90mA more than the maximum load current.

Note 4:

Specified output resistance includes the effect of the 0.2

Ω ESR of the test circuit’s capacitors.

Note 5:

The switches are driven directly at the oscillator frequency, without any division.

Note 6:

At lowest frequencies, using 10µF capacitors gives worse efficiency figures than using the recommended capacitor values in Table 3, due to larger 1 ⁄ (f s x C1) term in R

OUT

.

_______________________________________________________________________________________ 3

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

__________________________________________Typical Operating Characteristics

(All curves generated using the inverter circuit shown in the Typical Operating Circuits with LV = GND and T

A

= +25°C, unless otherwise noted. Test results also valid for doubler mode with LV = OUT and T

A

= +25°C. All capacitor values used are those recommended in Table 3, unless otherwise noted. The output resistance curves represent the resistance of the device itself, which is R

O in the equation for R

OUT shown in the Capacitor Selection section.)

OUTPUT VOLTAGE DROP FROM

SUPPLY VOLTAGE vs. LOAD CURRENT

OSCILLATOR FREQUENCY vs.

SUPPLY VOLTAGE

OUTPUT SOURCE RESISTANCE (R

O

) vs.

SUPPLY VOLTAGE

2

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0

ALL FREQUENCIES

V

DD

= +1.5V

V

DD

= +2.5V

V

DD

= +3.5V

V

DD

= +4.5V, +5.0V

V

DD

= +5.5V

10 20 30

LOAD CURRENT (mA)

40 50

0

-2

-4

-6

-8

-10

-12

ALL FREQUENCIES,

LV CONNECTED TO GND

(INVERTER) OR OUT (DOUBLER)

-14

1.0

1.5 2.0

2.5

3.0

3.5

4.0

4.5 5.0 5.5

SUPPLY VOLTAGE (V)

20

18

16

14

12

10

8

6

4

2

0

0 1 2

ALL FREQUENCIES

3 4

SUPPLY VOLTAGE (V)

5

OUTPUT SOURCE RESISTANCE (R

O

) vs.

TEMPERATURE

MAX860

EFFICIENCY vs. LOAD CURRENT

MAX860 SUPPLY CURRENT vs. SUPPLY VOLTAGE

32

28

24

20

16

12

8

4

0

ALL FREQUENCIES

V

DD

= +1.5V

V

DD

= +3V

V

DD

= +5V

-60 -40 -20 0 20 40 60 80

TEMPERATURE (°C)

100 120 140

100

90

80

70

60

50

40

30

20

10

0

0.01

V

DD

= +1.5V

V

DD

= +3V

V

DD

= +5V

INVERTER

FC = V

DD

0.1

1 10

LOAD CURRENT (mA)

100

500

400

300

200

100

0

0

FC = V

DD

1

DOUBLER, LV = OUT

INVERTER, LV = GND

(V

DD

> 3V)

2 3 4

SUPPLY VOLTAGE (V)

5 6

MAX861 SUPPLY CURRENT vs. SUPPLY VOLTAGE

500

FC = V

DD

400

DOUBLER, LV = OUT

300

200

100

0

0

INVERTER, LV = GND

1 2 3 4

SUPPLY VOLTAGE (V)

5 6

70

MAX860 OUTPUT CURRENT vs. CAPACITANCE

HIGH-FREQUENCY MODE

60

50

40 f

OSC

= 130kHz

FC = OUT

LV = GND

INVERTER MODE

V

IN

= +4.5V, V

OUT

= -3.5V

V

IN

= +4.5V, V

OUT

= -4V

30

V

IN

= +3V, V

OUT

= -2.4V

20

V

IN

= +3V, V

OUT

= -2.7V

10

0

0.33

1 2.2

4.7

CAPACITANCE (

µF)

10 22

80

MAX860 OUTPUT CURRENT vs. CAPACITANCE

MEDIUM-FREQUENCY MODE

70

60 f

OSC

= 50kHz

FC = GND

LV = GND

INVERTER MODE

V

IN

= +4.5V, V

OUT

= -3.5V

50

40

V

IN

= +3V, V

OUT

= -2.4V

30

20

10

0

0.33

V

IN

= +4.5V, V

OUT

= -4V

V

IN

= +3V, V

OUT

= -2.7V

1 2.2

4.7

CAPACITANCE (

µF)

10 22

4 _______________________________________________________________________________________

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

____________________________Typical Operating Characteristics (continued)

(All curves generated using the inverter circuit shown in the Typical Operating Circuits with LV = GND and T

A

= +25°C, unless otherwise noted. Test results also valid for doubler mode with LV = OUT and T

A

= +25°C. All capacitor values used are those recommended in Table 3, unless otherwise noted. The output resistance curves represent the resistance of the device itself, which is R

O in the equation for R

OUT shown in the Capacitor Selection section.)

MAX861

OUTPUT CURRENT vs. CAPACITANCE

HIGH-FREQUENCY MODE

90

80

70 f

OSC

= 250kHz

FC = OUT

LV = GND

INVERTER MODE

60

50

40

30

V

IN

= +4.5V, V

OUT

V

IN

= +4.5V,

V

OUT

= -3.5V

= -4V

V

IN

= +3V, V

OUT

= -2.4V

20

10

0

0.33

V

IN

= +3V, V

OUT

= -2.7V

1 2.2

4.7

CAPACITANCE (

µF)

10 22

80

70

60

50

40

30

20

10

0

0.33

MAX861

OUTPUT CURRENT vs. CAPACITANCE

MEDIUM-FREQUENCY MODE

f

OSC

= 100kHz

FC = GND

LV = GND

INVERTER MODE

V

IN

= +4.5V,

V

OUT

= -3.5V

V

IN

= +3V,

V

OUT

= -2.4V

V

IN

= +4.5V,

V

OUT

= -4V

V

IN

= +3V, V

OUT

= -2.7V

1 2.2

4.7

CAPACITANCE (

µF)

10 22

______________________________________________________________Pin Description

PIN

5

6

3

4

1

2

7

8

NAME

FC

C1+

GND

C1-

OUT

LV

–

S H

—

D

— –

N

V

DD

INVERTER

Frequency Control, see Table 1

Flying-Capacitor Positive Terminal

Ground

Flying-Capacitor Negative Terminal

Negative Output

Low-Voltage-Operation Input. Connect to GND.

FUNCTION

DOUBLER

Frequency Control, see Table 1

Flying-Capacitor Positive Terminal

Positive Input Supply

Flying-Capacitor Negative Terminal

Ground

Low-Voltage-Operation Input. Connect to OUT.

Active-Low Shutdown Input. Connect to V

DD if not used. Connect to GND to disable the charge pump.

Positive Input Supply

Active-Low Shutdown Input. Connect to GND pin if not used. Connect to OUT to disable the charge pump.

Doubled Positive Output

_______________________________________________________________________________________

5

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

_______________Detailed Description

The MAX860/MAX861 capacitive charge pumps either invert or double the voltage applied to their inputs. For highest performance, use low equivalent series resistance (ESR) capacitors. See the Capacitor Selection section for more details. The frequency-control (FC) pin allows you to choose one of three switching frequencies; these three selectable frequencies are different for each device. When shut down, MAX860/MAX861 current consumption reduces to less than 1µA.

Common Applications

Voltage Inverter

The most common application for these devices is a charge-pump voltage inverter (see Typical Operating

Circuits). This application requires only two external components—capacitors C1 and C2—plus a bypass capacitor if necessary (see Bypass Capacitor section). Refer to the

Capacitor Selection section for suggested capacitor types and values.

Even though the MAX860/MAX861’s output is not actively regulated, it is fairly insensitive to load-current changes. A circuit output source resistance of 12

Ω (calculated using the formula given in the Capacitor Selection section) means that, with a +5V input, the output voltage is -5V under no load and decreases to -4.4V with a 50mA load.

The MAX860/MAX861 output source resistance (used to calculate the circuit output source resistance) vs. temperature and supply voltage are shown in the Typical

Operating Characteristics graphs.

Calculate the output ripple voltage using the formula given in the Capacitor Selection section.

Positive Voltage Doubler

The MAX860/MAX861 can also operate as positive voltage doublers (see Typical Operating Circuits). This application requires only two external components, capacitors C1 and C2. The no-load output is twice the input voltage. The electrical specifications in the doubler mode are very similar to those of the inverter mode except for the Supply Voltage Range (see Electrical

Characteristics table) and No-Load Supply Current (see graph in Typical Operating Characteristics). The circuit output source resistance and output ripple voltage are calculated using the formulas in the Capacitor Selection section.

Active-Low Shutdown Input

When driven low, the S H D N device. In inverter mode, connect

–

S not used. In doubler mode, connect

—

H

—

—

S

–

—

H

—

D

–

N to V

DD if it is to GND if it is not used. When the device is shut down, all active circuitry is turned off.

In the inverting configuration, loads connected from

OUT to GND are not powered in shutdown mode.

However, a reverse-current path exists through two diodes between OUT and GND; therefore, loads connected from V

DD to OUT draw current from the input supply.

In the doubling configuration, loads connected from the

V

DD pin to the GND pin are not powered in shutdown mode. Loads connected from the V

DD pin to the OUT pin draw current from the input supply through a path similar to that of the inverting configuration (described above).

Frequency Control

Charge-pump frequency for both devices can be set to one of three values. Each device has a unique set of three available frequencies, as indicated in Table 1.

The oscillator and charge-pump frequencies are the same (i.e., the charge-pump frequency is not half the oscillator frequency, as it is on the MAX660, MAX665, and ICL7660).

Table 1. Nominal Switching Frequencies*

FC CONNECTION

FC = V

DD or open

FC = GND

FC = OUT

FREQUENCY (kHz)

MAX860 MAX861

6

50

130

13

100

250

*See the Electrical Characteristics for detailed switchingfrequency specifications.

A higher switching frequency minimizes capacitor size for the same performance and increases the supply current (Table 2). The lowest fundamental frequency of the switching noise is equal to the minimum specified switching frequency (e.g., 3kHz for the MAX860 with FC open). The spectrum of noise frequencies extends above this value because of harmonics in the switching waveform. To get best noise performance, choose the device and FC connection to select a minimum switching frequency that lies above your sensitive bandwidth.

Low-Voltage-Operation Input

LV should be connected to GND for inverting operation.

To enhance compatibility with the MAX660, MAX665, and

ICL7660, you may float LV if the input voltage exceeds 3V.

In doubling mode, LV must be connected to OUT for all input voltages.

6 _______________________________________________________________________________________

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

Table 2. Switching-Frequency Trade-Offs

ATTRIBUTE

Output Ripple

C1, C2 Values

Supply Current

LOWER

FREQUENCY

Larger

Larger

Smaller

HIGHER

FREQUENCY

Smaller

Smaller

Larger

__________Applications Information

Capacitor Selection

The MAX860/MAX861 are tested using 10µF capacitors for both C1 and C2, although smaller or larger values can be used (Table 3). Smaller C1 values increase the output resistance; larger values reduce the output resistance. Above a certain point, increasing the capacitance of C1 has a negligible effect (because the output resistance becomes dominated by the internal switch resistance and the capacitor ESR). Low-ESR capacitors provide the lowest output resistance and ripple voltage. The output resistance of the entire circuit

(inverter or doubler) is approximately:

R

OUT

= R

O

+ 4 x ESR

C1

+ ESR

C2

+ 1 / (f

S x C1) where R

O

(the effective resistance of the MAX860/

MAX861’s internal switches) is approximately 8

Ω and f

S is the switching frequency. R

OUT is typically 12

Ω when using capacitors with 0.2

Ω ESR and f

S

, C1, and C2 values suggested in Table 3. When C1 and C2 are so large (or the switching frequency is so high) that the internal switch resistance dominates the output resistance, estimate the output resistance as follows:

R

OUT

= R

O

+ 4 x ESR

C1

+ ESR

C2

A typical design procedure is as follows:

1) Choose C1 and C2 to be the same, for convenience.

2) Select f

S

: a) If you want to avoid a specific noise frequency, choose f

S appropriately.

b) If you want to minimize capacitor cost and size, choose a high f

S

.

c) If you want to minimize current consumption, choose a low f

S

.

3) Choose a capacitor based on Table 3, although higher or lower values can be used to optimize performance. Table 4 lists manufacturers who provide low-ESR capacitors.

Table 3. Suggested Capacitor Values*

NOMINAL FREQUENCY (kHz)

6

13

50

100

130

250

C1, C2 (µF)

4.7

4.7

2.2

68

47

10

*In addition to Table 3, four graphs in the Typical

Operating Characteristics section show typical output current for C1 and C2 capacitances ranging from

0.33µF to 22µF. Output current is plotted for inputs of

4.5V (5V - 10%) and 3.0V (3.3V - 10%), and also for

10% and 20% output droop from the ideal -V

IN value.

Table 4. Low-ESR Capacitor Manufacturers

MANUFACTURER–Series

AVX TPS Series

AVX TAG Series

Matsuo 267 Series

PHONE

(803) 946-0629

(803) 946-0629

(714) 969-2491

Sprague 595 Series

Sanyo MV-GX Series

Sanyo CV-GX Series

Nichicon PL Series

(603) 224-1961

(619) 661-6835

(619) 661-6835

(847) 843-7500

United Chemicon (Marcon) (847) 696-2000

TDK (847) 390-4461

FAX

(803) 626-3123

(803) 626-3123

(714) 960-6492

(613) 224-1430

(619) 661-1055

(619) 661-1055

(847) 843-2798

(847) 696-9278

(847) 390-4405

COMMENTS

Low-ESR tantalum, SMT

Low-cost tantalum, SMT

Low-cost tantalum, SMT

Low-ESR tantalum, SMT

Aluminum electrolytic, through hole

Aluminum electrolytic, SMT

Aluminum electrolytic, through hole

Ceramic SMT

Ceramic SMT

_______________________________________________________________________________________ 7

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

Flying Capacitor, C1

Increasing the size of the flying capacitor reduces the output resistance.

Output Capacitor, C2

Increasing the size of the output capacitor reduces the output ripple voltage. Decreasing its ESR reduces both output resistance and ripple. Smaller capacitance values can be used if one of the higher switching frequencies is selected, if less than the maximum rated output current (50mA) is required, or if higher ripple can be tolerated. The following equation for peak-to-peak ripple applies to both the inverter and doubler circuits.

I

OUT

V

RIPPLE

= ———————— + 2 x I

OUT x ESR

C2

2 x f

S x C2

Bypass Capacitor

Bypass the incoming supply to reduce its AC impedance and the impact of the MAX860/MAX861’s switching noise. The recommended bypassing depends on the circuit configuration and where the load is connected.

When the inverter is loaded from OUT to GND or the doubler is loaded from V

DD to GND, current from the supply switches between 2 x I

OUT and zero. Therefore, use a large bypass capacitor (e.g., equal to the value of C1) if the supply has a high AC impedance.

When the inverter and doubler are loaded from V

DD to

OUT, the circuit draws 2 x I

OUT constantly, except for short switching spikes. A 0.1µF bypass capacitor is sufficient.

Cascading Devices

Two devices can be cascaded to produce an even larger negative voltage, as shown in Figure 1. The unloaded output voltage is nominally -2 x V

IN

, but this is reduced slightly by the output resistance of the first device multiplied by the quiescent current of the second. The output resistance of the complete circuit is approximately five times the output resistance of a single MAX860/MAX861.

Three or more devices can be cascaded in this way, but output resistance rises dramatically, and a better solution is offered by inductive switching regulators

(such as the MAX755, MAX759, MAX764, or MAX774).

Connect LV as with a standard inverter circuit (see Pin

Description).

The maximum load current and startup current of nth cascaded circuit must not exceed the maximum output current capability of (n-1)th circuit to ensure proper startup.

Paralleling Devices

Paralleling multiple MAX860s or MAX861s reduces the output resistance. As illustrated in Figure 2, each device requires its own pump capacitor (C1), but the reservoir capacitor (C2) serves all devices. C2’s value should be increased by a factor of n, where n is the number of devices. Figure 2 shows the equation for calculating output resistance. An alternative solution is to use the MAX660 or MAX665, which are capable of supplying up to 100mA of load current. Connect LV as with a standard inverter circuit (see Pin Description).

Combined Doubler/Inverter

In the circuit of Figure 3, capacitors C1 and C2 form the inverter, while C3 and C4 form the doubler. C1 and C3 are the pump capacitors; C2 and C4 are the reservoir capacitors. Because both the inverter and doubler use part of the charge-pump circuit, loading either output causes both outputs to decline towards GND. Make

C1

2

3

4

MAX860

MAX861

“1”

5

8

7

+V

IN

…

2

C1

3

…

C2

4

8

7

MAX860

MAX861

“n”

5

V

OUT

C2

V

OUT

= -nV

IN

C1

2

3

4

MAX860

MAX861

“1”

5

8

7

R

OUT

=

R

OUT

OF SINGLE DEVICE

NUMBER OF DEVICES

…

+V

IN

8

2 7

3

C1

4

MAX860

MAX861

“n”

5

…

V

OUT

= -V

IN

V

OUT

C2

Figure 1. Cascading MAX860s or MAX861s to Increase

Output Voltage

Figure 2. Paralleling MAX860s or MAX861s to Reduce Output

Resistance

8 _______________________________________________________________________________________

C1

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

2

3

4

MAX860

MAX861

C3

8

7

+V

IN

5

D1

D1, D2 = 1N4148

V

OUT

= -V

IN

C2

D2

C4

V

OUT

= (2V

IN

) -

(V

FD1

) - (V

FD2

)

Table 5. Product Selection Guide

PART

NUMBER

MAX660

MAX665

MAX860

MAX861

ICL7660

OUTPUT

CURRENT

(mA)

OUTPUT

RESISTANCE

(

Ω)

SWITCHING

FREQUENCY

(kHz)

100

100

6.5

6.5

5/40

5/40

50

50

10

12

12

55

6/50/130

13/100/250

5

Figure 3. Combined Doubler and Inverter

sure the sum of the currents drawn from the two outputs does not exceed 60mA. Connect LV as with a standard inverter circuit (see Pin Description).

Compatibility with

MAX660/MAX665/ICL7660

The MAX860/MAX861 can be used in sockets designed for the MAX660, MAX665, and ICL7660 with a minimum of one wiring change. This section gives advice on installing a MAX860/MAX861 into a socket designed for one of the earlier devices.

instead of

–

S

—

H

—

D

–

N . MAX660, MAX665, and ICL7660 norbe overdriven). If OSC is floating, pin 7 (

–

S

—

H

—

D

–

N ) should be jumpered to V

DD permanently. Do not leave

—

S

—

H

—

D

–

N on the MAX860/

MAX861 floating.

The MAX860/MAX861 operate with FC either floating or connected to V

DD

, OUT, or GND; each connection defines the oscillator frequency. Thus, any of the normal MAX660, MAX665, or ICL7660 connections to pin 1 will work with the MAX860/MAX861, without modifications. Changes to the FC connection are only required if you want to adjust the operating frequency.

___________________Chip Topography

FC

C1+

GND

C1-

0.058"

(1.47mm)

TRANSISTOR COUNT: 101

SUBSTRATE CONNECTED TO V

DD

V

DD

0.084"

(2.13mm)

SHDN

LV

OUT

_______________________________________________________________________________________ 9

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to

www.maxim-ic.com/packages

.)

N

E H

1

TOP VIEW

D e

FRONT VIEW

B

A1

A

C

L

SIDE VIEW

0∞-8∞

DIM

E

H

L

A

A1

B

C e

INCHES

MIN MAX

0.053

0.004

0.014

0.007

0.069

0.010

0.019

0.010

0.050 BSC

0.150

0.228

0.016

0.157

0.244

0.050

MILLIMETERS

MIN MAX

1.35

0.10

0.35

0.19

1.75

0.25

0.49

0.25

1.27 BSC

3.80

5.80

0.40

4.00

6.20

1.27

VARIATIONS:

DIM

D

D

D

INCHES

MIN

0.189

0.337

0.386

MAX

0.197

0.344

0.394

MILLIMETERS

MIN

4.80

8.55

9.80

MAX

5.00

8.75

10.00

N MS012

8 AA

14

16

AB

AC

PROPRIETARY INFORMATION

TITLE:

PACKAGE OUTLINE, .150" SOIC

APPROVAL DOCUMENT CONTROL NO.

21-0041

REV.

B

1

1

10 ______________________________________________________________________________________

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to

www.maxim-ic.com/packages

.)

4X S

8

8

ÿ 0.50±0.1

E H

0.6±0.1

0.6±0.1

1

D

TOP VIEW

BOTTOM VIEW

1

L

α

S c

D e

E

H

DIM

A

A1

A2 b

INCHES

MIN

-

0.002

0.030

MAX

0.043

0.006

0.037

0.010

0.005

0.116

0.188

0.014

0.007

0.116

0.120

0.0256 BSC

0.120

0.198

0.016

0∞

0.026

6∞

0.0207 BSC

MILLIMETERS

MIN

MAX

1.10

0.05

0.75

0.15

0.95

0.25

0.13

0.36

0.18

2.95

3.05

0.65 BSC

2.95

4.78

3.05

5.03

0.41

0∞

0.66

6∞

0.5250 BSC

A2 e

FRONT VIEW b

A1

A c

L

SIDE VIEW

α

PROPRIETARY INFORMATION

TITLE:

PACKAGE OUTLINE, 8L uMAX/uSOP

APPROVAL DOCUMENT CONTROL NO.

21-0036

REV.

J

1

1

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

11 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600

© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.