Rainbow Electronics MAX861 User Manual

19-0239; Rev 1; 11/96

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 cir­cuitry. Each device has a unique set of three available
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 -25°C to +85°C
MAX860C/D 0°C to +70°C Dice*
MAX860ESA -40°C to +85°C 8 SO
MAX860MJA -55°C to +125°C
MAX861ISA
MAX861IUA -25°C to +85°C 8 µMAX
MAX861C/D 0°C to +70°C Dice*
MAX861ESA -40°C to +85°C 8 SO
MAX861MJA -55°C to +125°C

* Dice are tested at TA= +25°C, DC parameters only.

†

Contact factory for availability.

TEMP. RANGE PIN-PACKAGE

-25°C to +85°C

-25°C to +85°C 8 SO

8 SO
8 µMAX

8 CERDIP

8 CERDIP

†

†

MAX860/MAX861

INPUT
VOLTAGE
+1.5V TO +5.5V

INVERTED
NEGATIVE
OUTPUT

10µF

C2

DOUBLED
POSITIVE
OUTPUT

10µF

C2

__________________Pin Configuration

TOP VIEW

V

8

DD

SHDN

7

LV

6

OUT

5

C1+

GND

C1-

FC

1
2

MAX860

3

MAX861

4

SO/µMAX

Maxim Integrated Products

1

INPUT

VOLTAGE

+2.5V TO +5.5V

1

MAX860

FC

MAX861

2

C1+

3

GND

4

10µF

C1

C1

POSITIVE VOLTAGE DOUBLER

C1- OUT

VOLTAGE INVERTER

1

MAX860

FC

MAX861

2

C1+

3

GND

4

10µF

C1- OUT

________________________________________________________________

V

SHDN

V

SHDN

8

DD

7
6

LV

5

8

DD

7
6

LV

5

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone]

50mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (VDDto GND or GND to OUT)...................+6.0V

Input Voltage Range (LV, FC, –S—H—D—N–) ...................(OUT - 0.3V)

Continuous Output Current (OUT, V

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

Continuous Power Dissipation (T

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

Note 1: OUT may be shorted to GND for 1sec without damage, but shorting OUT to VDDmay damage the device and should be

avoided. Also, for temperatures above +85°C, OUT must not be shorted to GND or V
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.

MAX860/MAX861

ELECTRICAL CHARACTERISTICS

(Typical Operating Circuit (Inverter), VDD= +5V, –S—H—D—N–= VDD, FC = LV = GND, C1 = C2 = 10µF (Note 2), TA= T
otherwise noted. Typical values are at T

Supply Voltage

No-Load Supply Current

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

DD

= +70°C)

A

= +25°C.)

A

DD

RL= 1kΩ

MAX860I/E

MAX860M

MAX861I/E

MAX861M

V

I

DD

to (V

DD

+ 0.3V)

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, 10sec).............................+300°C

, even instantaneously, or device

DD

to T

MIN

CONDITIONS

Inverter, LV = GND
Doubler, LV = OUT
FC = VDD= 5V
FC = VDD= 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

1.5 5.5

2.5 5.5

0.2 0.3

0.07

0.6 1.0

1.4 2.5

0.4

1.3

3.3

0.3 0.4

1.1 2.0

2.5 5.0

0.5

2.6

6.5

MAX

, unless

UNITSMIN TYP MAXSYMBOLPARAMETER

V

mA

VDD= 5V, V

Output Current

Output Resistance
(Note 3)

2 _______________________________________________________________________________________

R

OUT

OUT

VDD= 3V, V
IL= 50mA

= 10mA, VDD= 2V

I

L

more negative than -3.75V

OUT

more negative than -2.5V

OUT

50 100

10 30

12 25
20 35

mAI

Ω

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

ELECTRICAL CHARACTERISTICS (continued)

(Typical Operating Circuit (Inverter), VDD= +5V, –S—H—D—N–= VDD, FC = LV = GND, C1 = C2 = 10µF (Note 2), TA= T
otherwise noted. Typical values are at T

Switching Frequency
(Note 4)

FC Current (from VDD)

Power Efficiency (Note 5)

= +25°C.)

A

CONDITIONS

MAX860

f

S

MAX861

FC < 4V

FC

MAX860,
FC = V

DD

MAX861,
FC = V

DD

MAX860/MAX861, FC = VDD,
IL= 50mA to GND, C1 = C2 = 68µF

FC = V

DD

FC = GND
FC = OUT
FC = V

DD

FC = GND
FC = OUT

RL= 2kΩ from V
to OUT

RL= 1kΩ from OUT
to GND

RL= 2kΩ from V
to OUT

RL= 1kΩ from OUT
to GND

DD

DD

36
30 50
80 130

813
60 100

160 250

93 96

90 93

93 96

88 92

87

MIN

to T

MAX

MAX860/MAX861

, unless

UNITSMIN TYP MAXSYMBOLPARAMETER

kHz

µA-2 -4I

%

No load
LV = GND

–
S—H—D—N–Threshold

Shutdown Supply Current

Note 2: C1 and C2 are low-ESR (<0.2Ω) aluminum electrolytics. Capacitor ESR adds to the circuit’s output resistance. Using
Note 3: Specified output resistance includes the effect of the 0.2Ω ESR of the test circuit’s capacitors.

Note 4: The switches are driven directly at the oscillator frequency, without any division.
Note 5: At lowest frequencies, using 10µF capacitors gives worse efficiency figures than using the recommended capacitor

capacitors with higher ESR may reduce output voltage and efficiency.

values in Table 3, due to larger 1 ⁄ (f

IH
IL

–

S—H—D—N–< 0.3V

No load, V

x C1) term in R

s

OUT

= -4V µs500Time to Exit Shutdown

OUT

MAX86_I/E
MAX86_M

.

1.2V

0.3V
1

10

%99 99.9Voltage-Conversion Efficiency

V

µA

_______________________________________________________________________________________ 3

50mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

__________________________________________Typical Operating Characteristics

(All curves generated using the inverter circuit shown in the
wise noted. Test results also valid for doubler mode with LV = OUT and TA= +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 ROin
the equation for R

shown in the

OUT

Capacitor Selection

OUTPUT VOLTAGE DROP FROM

SUPPLY VOLTAGE vs. LOAD CURRENT

0.8
ALL FREQUENCIES

0.7

0.6

0.5

0.4

DROP (V)

OUT

0.3

V

MAX860/MAX861

0.2

0.1

0

0

VDD = +1.5V

VDD = +5.5V

10 20 50

LOAD CURRENT (mA)

VDD = +2.5V

VDD = +3.5V

VDD = +4.5V, +5.0V

30

40

MAX860-01

2

= +5V)

0

DD

-2

-4

-6

-8

-10

-12

PERCENTAGE FREQUENCY CHANGE (%)

-14

(FROM FREQUENCY MEASURED WITH V

OUTPUT SOURCE RESISTANCE (RO) vs.

TEMPERATURE

32

ALL FREQUENCIES

28
24

20
16
12

8

OUTPUT SOURCE RESISTANCE (Ω)

4
0

-60 -20 40 140

-40 0 60 80 120

VDD = +3V

20 100

TEMPERATURE (°C)

VDD = +1.5V

VDD = +5V

MAX860-04

100

90
80
70
60
50
40

EFFICIENCY (%)

30
20
10

0

Typical Operating Circuits

section.)

OSCILLATOR FREQUENCY vs.

SUPPLY VOLTAGE

ALL FREQUENCIES,
LV CONNECTED TO GND 
(INVERTER) OR OUT (DOUBLER)

1.5 2.0 3.0 4.0

1.0

2.5 3.5

SUPPLY VOLTAGE (V)

4.5 5.0 5.5

MAX860

EFFICIENCY vs. LOAD CURRENT

VDD = +1.5V

VDD = +3V

VDD = +5V

INVERTER

FC = V

DD

0.01 1 100

0.1 10
LOAD CURRENT (mA)

with LV = GND and TA= +25°C, unless other-

OUTPUT SOURCE RESISTANCE (RO) vs.

SUPPLY VOLTAGE

20
18

MAX860-02

16
14
12
10

8
6
4

OUTPUT SOURCE RESISTANCE (Ω)

2
0

01 3 5

SUPPLY VOLTAGE (V)

ALL FREQUENCIES

24

MAX860 SUPPLY CURRENT

vs. SUPPLY VOLTAGE

500

FC = V

MAX860-05

400

300

200

SUPPLY CURRENT (µA)

100

DD

DOUBLER, LV = OUT

INVERTER, LV = GND

> 3V)

(V

DD

0

0

123456

SUPPLY VOLTAGE (V)

MAX860-03

MAX860-06

500

400

300

200

SUPPLY CURRENT (µA)

100

0

0

MAX861 SUPPLY CURRENT

vs. SUPPLY VOLTAGE

FC = V

DD

DOUBLER, LV = OUT

INVERTER, LV = GND

123456

SUPPLY VOLTAGE (V)

MAX860 OUTPUT CURRENT vs. CAPACITANCE

70

MAX860-07

60

50

40
30

20

OUTPUT CURRENT (mA)

10

0

0.33

HIGH-FREQUENCY MODE

f

= 130kHz

OSC

FC = OUT
LV = GND
INVERTER MODE

VIN = +4.5V, V

VIN = +4.5V, V

= -4V

OUT

VIN = +3V, V

VIN = +3V, V

1 2.2 22

CAPACITANCE (µF)

OUT

4.7

OUT

= -2.4V

OUT

= -2.7V

10

MAX860-08

= -3.5V

MAX860 OUTPUT CURRENT vs. CAPACITANCE

MEDIUM-FREQUENCY MODE

80

f

= 50kHz

OSC

FC = GND

70

LV = GND
INVERTER MODE

60
50

40
30

OUTPUT CURRENT (mA)

20
10

0

0.33

1 2.2 22

CAPACITANCE (µF)

4 _______________________________________________________________________________________

VIN = +4.5V, V

VIN = +3V, V

VIN = +4.5V, V

VIN = +3V, V

4.7

OUT

OUT

OUT

= -3.5V

= -2.4V

OUT

= -2.7V

10

MAX860-09

= -4V

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

____________________________Typical Operating Characteristics (continued)

(All curves generated using the inverter circuit shown in the
wise noted. Test results also valid for doubler mode with LV = OUT and TA= +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 ROin
the equation for R

shown in the

OUT

Capacitor Selection

MAX861

OUTPUT CURRENT vs. CAPACITANCE 

HIGH-FREQUENCY MODE

90

f

= 250kHz

OSC

80

FC = OUT
LV = GND

70

INVERTER MODE

60
50

VIN = +4.5V, V

40
30

OUTPUT CURRENT (mA)

20

VIN = +3V, V

10

0

0.33

1 2.2 22

CAPACITANCE (µF)

= -4V

OUT

VIN = +3V, V

= -2.7V

OUT

VIN = +4.5V, 

= -3.5V

V

OUT

= -2.4V

OUT

4.7

10

Typical Operating Circuits

section.)

MAX860-10

with LV = GND and TA= +25°C, unless other-

MAX861

OUTPUT CURRENT vs. CAPACITANCE 

MEDIUM-FREQUENCY MODE

80

f

= 100kHz

OSC

FC = GND

70

LV = GND
INVERTER MODE

60
50

40
30

OUTPUT CURRENT (mA)

20
10

0

0.33

VIN = +3V, 

= -2.4V

V

OUT

VIN = +3V, V

1 2.2 22

CAPACITANCE (µF)

VIN = +4.5V, 
V

OUT

VIN = +4.5V, 
V

OUT

= -2.7V

OUT

4.7

= -3.5V

MAX860-11

= -4V

10

______________________________________________________________Pin Description

NAMEPIN

INVERTER

FUNCTION

DOUBLER

MAX860/MAX861

Frequency Control, see Table 1FC1
Flying-Capacitor Positive Terminal C1+2
GroundGND3
Flying-Capacitor Negative TerminalC1-4
Negative OutputOUT5
Low-Voltage-Operation Input. Connect to GND.LV6

–

–

7

8

S—H—D—N

DD

Active-Low Shutdown Input. Connect to VDDif not
used. Connect to GND to disable the charge pump.

Positive Input SupplyV

_______________________________________________________________________________________

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 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
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

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

Circuits

MAX860/MAX861

ponents—capacitors C1 and C2—plus a bypass capacitor
if necessary (see

Capacitor Selection

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 12Ω (calculated using
the formula given in the
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

Operating Characteristics

Calculate the output ripple voltage using the formula
given in the

The MAX860/MAX861 can also operate as positive volt­age doublers (see
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

Characteristics

graph in
output source resistance and output ripple voltage are
calculated using the formulas in the
section.

). This application requires only two external com-

Bypass Capacitor

section for suggested capacitor types

Capacitor Selection

graphs.

Capacitor Selection

Typical Operating Circuits

table) and No-Load Supply Current (see

Typical Operating Characteristics

Active-Low Shutdown Input

When driven low, the –S—H—D—N–input shuts down the
device. In inverter mode, connect –S—H—D—N–to VDDif it is
not used. In doubler mode, connect –S—H—D—N–to GND if it

Capacitor Selection

Voltage Inverter

Typical Operating

section). Refer to the

section.

Positive Voltage Doubler

Electrical

). The circuit

Capacitor Selection

section)

Typical

). This

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
supply.

In the doubling configuration, loads connected from the
VDDpin to the GND pin are not powered in shutdown
mode. Loads connected from the VDDpin to the OUT
pin draw current from the input supply through a path
similar to that of the inverting configuration (described
above).

to OUT draw current from the input

DD

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 = VDDor open 6 13
FC = GND 50 100
FC = OUT 130 250

*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.

FREQUENCY (kHz)

MAX860 MAX861

6 _______________________________________________________________________________________

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

Table 2. Switching-Frequency Trade-Offs

ATTRIBUTE

Output Ripple Larger Smaller
C1, C2 Values Larger Smaller
Supply Current Smaller Larger

LOWER

FREQUENCY

HIGHER

FREQUENCY

__________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

= RO+ 4 x ESRC1+ ESRC2+ 1 / (fSx C1)

OUT

where RO(the effective resistance of the MAX860/
MAX861’s internal switches) is approximately 8Ω and f
is the switching frequency. R
using capacitors with 0.2Ω ESR and fS, 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

= RO+ 4 x ESRC1+ ESR

OUT

is typically 12Ω when

OUT

C2

A typical design procedure is as follows:

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

2) Select fS:
a) If you want to avoid a specific noise frequency,

choose fSappropriately.

b) If you want to minimize capacitor cost and size,

choose a high fS.

c) If you want to minimize current consumption,

choose a low fS.

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*

C1, C2 (µF)NOMINAL FREQUENCY (kHz)

6 68
13 47
50 10

100 4.7

S

*In addition to Table 3, four graphs in the

Operating Characteristics

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 -VINvalue.

130 4.7
250 2.2

section show typical output

MAX860/MAX861

Typical

Table 4. Low-ESR Capacitor Manufacturers

MANUFACTURER–Series PHONE FAX COMMENTS

AVX TPS Series [phone] [phone] Low-ESR tantalum, SMT
AVX TAG Series [phone] [phone] Low-cost tantalum, SMT
Matsuo 267 Series [phone] [phone] Low-cost tantalum, SMT
Sprague 595 Series [phone] [phone] Low-ESR tantalum, SMT
Sanyo MV-GX Series [phone] [phone] Aluminum electrolytic, through hole
Sanyo CV-GX Series [phone] [phone] Aluminum electrolytic, SMT
Nichicon PL Series [phone] [phone] Aluminum electrolytic, through hole
United Chemicon (Marcon) [phone] [phone] Ceramic SMT
TDK [phone] [phone] 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

V

RIPPLE

= ———————— + 2 x I

MAX860/MAX861

OUT

2 x fSx C2

OUT

x ESR

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 VDDto GND, current from the
supply switches between 2 x I

and zero. Therefore,

OUT

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 VDDto
OUT, the circuit draws 2 x I

constantly, except for

OUT

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

C2

unloaded output voltage is nominally -2 x V

, but this is

IN

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 sin-

gle 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

Description

).

Pin

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
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

).

OF SINGLE DEVICE

R

OUT

R

=

OUT

+V

IN

…

NUMBER OF DEVICES

…

…

+V

IN

8

22
33

C1

MAX860
MAX861

445

“1”

7

C1

MAX860
MAX861

“n”

…

C2

V

OUT

Figure 1. Cascading MAX860s or MAX861s to Increase
Output Voltage

8 _______________________________________________________________________________________

= -nV

8

7

V

OUT

5

C2

IN

Figure 2. Paralleling MAX860s or MAX861s to Reduce Output
Resistance

22
33

MAX860
MAX861

445

“1”

8
7

C1C1

8

7

MAX860
MAX861

“n”

= -V

V

OUT

IN

V

OUT

5

C2

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

+V

IN

8

2
3

C1

MAX860
MAX861

4

7

5

C3

D1, D2 = 1N4148

D1

D2

V

= -V

OUT

IN

C2

V

= (2VIN) -

OUT

(V

) - (V

)

FD1

C4

FD2



Figure 3. Combined Doubler and Inverter

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.

The MAX660, MAX665, and ICL7660 have an OSC pin
instead of –S—H—D—N–. MAX660, MAX665, and ICL7660 nor­mal operation is with OSC floating (although OSC can
be overdriven). If OSC is floating, pin 7 (–S—H—D—N–) should
be jumpered to VDDto enable the MAX860/MAX861
permanently. Do not leave –S—H—D—N–on the MAX860/
MAX861 floating.

The MAX860/MAX861 operate with FC either floating or
connected to VDD, 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.

Table 5. Product Selection Guide

PART

NUMBER

MAX660 100 6.5 5/40

MAX665 100 6.5 5/40

MAX860 50 12 6/50/130

MAX861 50 12 13/100/250

ICL7660 10 55 5

OUTPUT

CURRENT

(mA)

OUTPUT

RESISTANCE

(Ω)

SWITCHING

FREQUENCY

(kHz)

___________________Chip Topography

C1+

GND

C1-

FC

0.058"

(1.47mm)

V

DD

0.084"

(2.13mm)

SHDN
LV

OUT

MAX860/MAX861

TRANSISTOR COUNT: 101
SUBSTRATE CONNECTED TO V

_______________________________________________________________________________________ 9

DD

50mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

________________________________________________________Package Information

CDIPS.EPS

MAX860/MAX861

SOICN.EPS

10 ______________________________________________________________________________________

50mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

___________________________________________Package Information (continued)

8LUMAXD.EPS

MAX860/MAX861

______________________________________________________________________________________ 11

50mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

NOTES

MAX860/MAX861

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.

12

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