General Description
The MAX1044 and ICL7660 are monolithic, CMOS
switched-capacitor voltage converters that invert, double,
divide, or multiply a positive input voltage. They are
pin compatible with the industry-standard ICL7660 and
LTC1044. Operation is guaranteed from 1.5V to 10V with
no external diode over the full temperature range. They
deliver 10mA with a 0.5V output drop. The MAX1044 has
a BOOST pin that raises the oscillator frequency above
the audio band and reduces external capacitor size
requirements.
The MAX1044/ICL7660 combine low quiescent current and
high efficiency. Oscillator control circuitry and four power
MOSFET switches are included on-chip. Applications
include generating a -5V supply from a +5V logic supply
to power analog circuitry. For applications requiring more
power, the MAX660 delivers up to 100mA with a voltage
drop of less than 0.65V.
Applications
●-5V Supply from +5V Logic Supply
●Personal Communications Equipment
●Portable Telephones
●Op-Amp Power Supplies
●EIA/TIA-232E and EIA/TIA-562 Power Supplies
●Data-Acquisition Systems
●Hand-Held Instruments
●Panel Meters
Features
● Miniature μMAX Package
●1.5V to 10.0V Operating Supply Voltage Range
●98% Typical Power-Conversion Efficiency
●Invert, Double, Divide, or Multiply Input Voltages
●BOOST Pin Increases Switching Frequencies
(MAX1044)
● No-Load Supply Current: 200μA Max at 5V
●No External Diode Required for Higher-Voltage
Operation
19-4667; Rev 2; 2/17
Ordering Information appears at end of data sheet.
NEGATIVE VOLTAGE CONVERTER
CAP+
CAP-
V+
VOUT
GND
INPUT
SUPPLY
VOLTAGE
NEGATIVE
OUTPUT
VOLTAGE
MAX1044
ICL7660
MAX1044
ICL7660
+
4
3
2
1
CAP-
GND
CAP+
(N.C.) BOOST
5
6
7
8
VOUT
LV
OSC
V+
TOP VIEW
( ) ARE FOR ICL7660
DIP/SO/µMAX
TO-99
ICL7660
N.C.
CAP+
GND
CAP-
VOUT
LV
OSC
V+ AND CASE
1
2
3
4
5
6
7
8
Typical Operating Circuit
Pin Congurations
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
Supply Voltage (V+ to GND, or GND to VOUT)..................10.5V
Input Voltage on Pins 1, 6, and 7 ....... -0.3V ≤ VIN ≤ (V+ + 0.3V)
LV Input Current ..................................................................20μA
Output Short-Circuit Duration (V+ ≤ 5.5V) ................Continuous
Continuous Power Dissipation (TA = +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW
SO (derate 5.88mW/°C above +70°C) ........................471mW
μMAX (derate 4.1mW/°C above +70°C) .....................330mW
CERDIP (derate 8.00mW/°C above +70°C) ................640mW
TO-99 (derate 6.67mW/°C above +70°C) ...................533mW
Operating Temperature Ranges
MAX1044C_ _ /ICL7660C_ _ .............................0°C to +70°C
MAX1044E_ _ /ICL7660E_ _ ......................... -40°C to +85°C
MAX1044M_ _ /ICL7660M_ _ ...................... -55°C to +125°C
Storage Temperature Range ........................... -65°C to + 150°C
Lead Temperature (soldering, 10sec) .............................+300°C
(Circuit of Figure 1, V+ = 5.0V, LV pin = 0V, BOOST pin = open, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.)
Note 1: The Maxim ICL7660 and MAX1044 can operate without an external output diode over the full temperature and voltage
ranges. The Maxim ICL7660 can also be used with an external output diode in series with pin 5 (cathode at VOUT) when
replacing the Intersil ICL7660. Tests are performed without diode in circuit.
Note 2: fOSC is tested with COSC = 100pF to minimize the effects of test fixture capacitance loading. The 1pF frequency is
correlated to this 100pF test point, and is intended to simulate pin 7’s capacitance when the device is plugged into a
test socket with no external capacitor. For this test, the LV pin is connected to GND for comparison to the original
manufacturer’s device, which automatically connects this pin to GND for (V+ > 3V).
Absolute Maximum Ratings
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
PARAMETER CONDITIONS MAX1044 ICL7660 UNITS
MIN TYP MAX MIN TYP MAX
Supply Current
R
L
= ∞,
pins 1 and 7
no connection,
LV open
T
A
= +25°C 30 200 80 175
µA
T
A
= 0°C to +70°C 200 225
T
A
= -40°C to +85°C 200 250
T
A
= -55°C to +125°C 200 250
R
L
= ∞, pins 1 and 7 = V+ = 3V 10
Supply Voltage
Range (Note 1)
R
L
= 10kΩ, LV open 3.0 10.0 V
R
L
= 10kΩ, LV to GND 1.5 10 1.5 3.5
Output Resistance
I
L
= 20mA,
f
OSC
= 5kHz,
LV open
T
A
= +25°C 65 100 55 100
Ω
T
A
= 0°C to +70°C 130 120
T
A
= -40°C to +85°C 130 140
T
A
= -55°C to +125°C 150 150
f
OSC
= 2.7kHz (ICL7660),
f
OSC
= 1kHz (MAX1044),
V+ = 2V, I
L
= 3mA,
LV to GND
T
A
= +25°C 325 250
T
A
= 0°C to +70°C 325 300
T
A
= -40°C to +85°C 325 300
T
A
= -55°C to +125°C 400 400
Oscillator Frequency C
OSC
= 1pF,
LV to GND (Note 2)
V+ = 5V 5 10 kHz
V+ = 2V 1
Power Efciency R
L
= 5kΩ, T
A
= +25°C, f
OSC
5kHz, LV open 95 98 95 98 %
Voltage Conversion Efciency R
L
= ∞, T
A
= +25°C, LV open
97.0
99.9
99.0
99.9 %
Oscillator Sink or
Source Current
V
OSC
= 0V or V+,
LV open
Pin 1 = 0V 3 µA
Pin 1 = V+ 20
Oscillator Impedance T
A
= +25°C V+ = 2V 1.0 1.0 MΩ
V+ = 5V 100 100 kΩ
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
2
(V+ = 5V; CBYPASS = 0.1μF; C1 = C2 = 10μF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)
Typical Operating Characteristics
OUTPUT VOLTAGE AND OUTPUT RIPPLE
vs. LOAD CURRENT
MAX1044-Fig 1
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
OUTPUT RIPPLE (mVp-p)
987654321
-0.5
-1.0
-1.5
-2.0
0
100
50
200
150
300
250
400
350
0
0 10
OUTPUT
VOLTAGE
V+ = 2V
LV = GND
OUTPUT RIPPLE
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
A
B
C
EFFICIENCY AND SUPPLY CURRENT
vs. LOAD CURRENT
MAX1044-Fig 4
LOAD CURRENT (mA)
EFFICIENCY (%)
7 8 964 52 31
100 10
9
8
7
6
5
4
3
2
1
0 0
0 10
SUPPLY CURRENT (mA)
10
40
50
60
70
80
90
30
20
SUPPLY CURRENT
EFFICIENCY
V+ = 2V
LV = GND
OUTPUT VOLTAGE AND OUTPUT RIPPLE
vs. LOAD CURRENT
MAX1044-Fig 2
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
353020 2510 155
-5.0 800
720
640
560
480
400
320
240
160
80
0 0
0 40
-0.5
-2.0
-2.5
-3.0
-3.5
-4.0
-4.5
-1.5
-1.0
OUTPUT RIPPLE (mVp-p)
OUTPUT VOLTAGE
OUTPUT RIPPLE
V+ = 5V
LV = OPEN
A
A
B
C
B
C
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
EFFICIENCY AND SUPPLY CURRENT
vs. LOAD CURRENT
MAX1044-Fig 5
LOAD CURRENT (mA)
EFFICIENCY (%)
353020 2510 155
100 50
45
40
35
30
25
20
15
10
5
0 0
0 40
SUPPLY CURRENT (mA)
10
40
50
60
70
80
90
30
20
V+ = 5V
LV = OPEN
EFFICIENCY
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
SUPPLY CURRENT
B
C
A
OUTPUT VOLTAGE AND OUTPUT RIPPLE
vs. LOAD CURRENT
MAX1044-Fig 3
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
353020 2510 155
-10 700
630
560
490
420
350
280
210
140
70
0 0
0 40
OUTPUT RIPPLE (mVp-p)
-1
-4
-5
-6
-7
-8
-9
-3
-2
V+ = 10V
LV = OPEN
OUTPUT
RIPPLE
A
B
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
C
B
C
A
OUTPUT
VOLTAGE
EFFICIENCY AND SUPPLY CURRENT
vs. LOAD CURRENT
MAX1044-Fig 6
LOAD CURRENT (mA)
EFFICIENCY (%)
353020 2510 155
100 50
45
40
35
30
25
20
15
10
5
0 0
0 40
SUPPLY CURRENT (mA)
10
40
50
60
70
80
90
30
20
V+ = 10V
LV = OPEN
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
SUPPLY CURRENT
B, C
EFFICIENCY
A
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
Maxim Integrated
│
3
www.maximintegrated.com
OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX1044-Fig 10
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
1007550250-25
20
40
60
80
100
0
-50 125
A: MAX1044 WITH
BOOST = V+
B: ICL7600
C: MAX1044 WITH
BOOST = OPEN
B
A
C
QUIESCENT CURRENT
vs. OSCILLATOR FREQUENCY
MAX1044-Fig 11
OSCILLATOR FREQUENCY (Hz)
QUIESCENT CURRENT (μA)
105
104
103
102
10
100
1000
10,000
1
1001015x105
USING
EXTERNAL
HCMOS
OSCILLATOR
USING
EXTERNAL
CAPACITOR
EFFICIENCY
vs. OSCILLATOR FREQUENCY
MAX1044-Fig 7
OSCILLATOR FREQUENCY (Hz)
EFFICIENCY (%)
105
104
103
102
40
50
60
70
80
90
100
30
1016x105
C1, C2 = 100µF
C1, C2 = 10µF
C1, C2 = 1µF
EXTERNAL
HCMOS
OSCILLATOR
OSCILLATOR FREQUENCY
vs. EXTERNAL CAPACITANCE
MAX1044-Fig 8
COSC (pF)
OSCILLATOR FREQUENCY (Hz)
10,000100010010
1
10
100
1000
10,000
100,000
0.1
1100,000
ICL7660 AND
MAX1044 WITH
BOOST = OPEN
MAX1044 WITH
BOOST -V+
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX1044-Fig 9
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (Hz)
98765432
1000
10,000
100,000
0
1 10
FROM TOP TO BOTTOM AT 5V
MAX1044, BOOST = V+, LV = GND
MAX1044, BOOST = V+, LV = OPEN
ICL7660, LV = GND
ICL7660, LV = OPEN
MAX1044, BOOST = OPEN, LV = GND
MAX1044, BOOST = OPEN, LV = OPEN
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
Maxim Integrated
│
4
www.maximintegrated.com
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
(V+ = 5V; CBYPASS = 0.1μF; C1 = C2 = 10μF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)
Typical Operating Characteristics (continued)
QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
1044-Fig 12
SUPPLY VOLTAGE (V)
QUIESCENT CURRENT (μA)
98765432
1
10
100
1000
2000
0.1
1 10
A
B
D
C
A: MAX1044, BOOST = V+, LV = GND
B: MAX1044, BOOST = V+, LV = OPEN
C: ICL7660 AND MAX1044 WITH
BOOST = OPEN, LV = GND;
ABOVE 5V, MAX1044 ONLY
D: ICL7660 AND MAX1044 WITH
BOOST = OPEN, LV = OPEN
QUIESCENT CURRENT
vs. TEMPERATURE
MAX1044-Fig 13
TEMPERATURE (°C)
QUIESCENT CURRENT (μA)
1007550250-25
100
200
300
400
500
0
-50 125
ICL7660, MAX1044 WITH BOOST = OPEN
MAX1044 WITH
BOOST = V+
OUTPUT RESISTANCE
vs. OSCILLATOR FREQUENCY
MAX1044-Fig 14
FREQUENCY (Hz)
RESISTANCE (Ω)
105
104
103
102
200
100
400
300
700
600
500
1000
900
800
0
101
C1, C2 = 100µF
C1, C2 = 1µF
C1, C2 = 10µF
EXTERNAL
HCMOS
OSCILLATOR
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
MAX1044-Fig 15
SUPPLY VOLTAGE (V)
OUTPUT RESISTANCE (Ω)
98765432
20
80
60
40
120
100
180
160
140
200
0
1 10
OUTPUT RESISTANCE
vs. TEMPERATURE
MAX1044-Fig 16
TEMPERATURE (°C)
OUTPUT RESISTANCE (Ω)
120100806040200-20-40
30
40
50
60
70
80
20
-60 140
ICL7660,
MAX1044 WITH
BOOST = OPEN
MAX1044 WITH
BOOST = V+
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
Maxim Integrated
│
5
www.maximintegrated.com
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
Detailed Description
The MAX1044/ICL7660 are charge-pump voltage
converters. They work by first accumulating charge in
a bucket capacitor and then transfer it into a reservoir
capacitor. The ideal voltage inverter circuit in Figure 2
illustrates this operation.
During the first half of each cycle, switches S1 & S3
close and switches S2 & S4 open, which connects the
bucket capacitor C1 across V+ and charges C1. During the
second half of each cycle, switches S2 & S4 close and
switches S1 & S3 open, which connects the positive
terminal of C1 to ground and shifts the negative terminal
to VOUT. This connects C1 in parallel with the reservoir
capacitor C2. If the voltage across C2 is smaller than the
voltage across C1, then charge flows from C1 to C2 until the
voltages across them are equal. During successive cycles,
C1 will continue pouring charge into C2 until the voltage
across C2 reaches - (V+). In an actual voltage inverter, the
output is less than - (V+) since the switches S1–S4 have
resistance and the load drains charge from C2.
Additional qualities of the MAX1044/ICL7660 can be
understood by using a switched-capacitor circuit model.
Switching the bucket capacitor, C1, between the input and
output of the circuit synthesizes a resistance (Figures 3a
and 3b.)
When the switch in Figure 3a is in the left position,
capacitor C1 charges to V+. When the switch moves
to the right position, C1 is discharged to VOUT. The
charge transferred per cycle is: ΔQ = C1(V+ - VOUT).
If the switch is cycled at frequency f, then the resulting
current is: I = f x ΔQ = f x C1(V+ - VOUT). Rewriting
this equation in Ohm’s law form defines an equivalent
resistance synthesized by the switched-capacitor circuit
where:
( )
OUT
EQUIV
VV
I1/ ( f x C1)
and
1
Rf x C1
+−
=
=
Figure 1. Maxim MAX1044/ICL7660 Test Circuit
Pin Description
PIN NAME FUNCTION
1
BOOST
(MAX1044)
Frequency Boost. Connecting BOOST to V+ increases the oscillator frequency by a factor of six.
When the oscillator is driven externally, BOOST has no effect and should be left open.
N.C.
(ICL7660) No Connection
2 CAP+ Connection to positive terminal of Charge-Pump Capacitor
3 GND Ground. For most applications, the positive terminal of the reservoir capacitor is connected to this pin.
4 CAP- Connection to negative terminal of Charge-Pump Capacitor
5 VOUT
Negative Voltage Output. For most applications, the negative terminal of the reservoir capacitor is
connected to this pin.
6LV Low-Voltage Operation. Connect to ground for supply voltages below 3.5V.
ICL7660: Leave open for supply voltages above 5V.
7 OSC Oscillator Control Input. Connecting an external capacitor reduces the oscillator frequency. Minimize stray
capacitance at this pin.
8 V+ Power-Supply Positive Voltage Input. (1.5V to 10V). V+ is also the substrate connection.
MAX1044
ICL7660
BOOST
CAP+
GND
C
BYPASS
= 0.1µF
V+
RL
CAP-
V+
OSC
C1
10µF
LV
VOUT
C2
10µF
COSC
EXTERNAL
OSCILLATOR
VOUT
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
6
Design Information
The MAX1044/ICL7660 are designed to provide a simple,
compact, low-cost solution where negative or doubled
supply voltages are needed for a few low-power com-
ponents. Figure 5 shows the basic negative voltage
converter circuit. For many applications, only two external
capacitors are needed. The type of capacitor used is not
critical.
Proper Use of the Low-Voltage (LV) Pin
Figure 4 shows an internal voltage regulator inside
the MAX1044/ICL7660. Use the LV pin to bypass this
regulator, in order to improve low-voltage performance
and allow operation down to 1.5V. For low-voltage opera-
tion and compatibility with the industry-standard LTC1044
and ICL7660, the LV pin should be connected to ground
for supply voltages below 3.5V and left open for supply
voltages above 3.5V.
The MAX1044’s LV pin can be grounded for all operat-
ing conditions. The advantage is improved low-voltage
performance and increased oscillator frequency. The
disadvantage is increased quiescent current and reduced
efficiency at higher supply voltages. For Maxim’s ICL7660,
the LV pin must be left open for supply voltages above 5V.
When operating at low supply voltages with LV open,
connections to the LV, BOOST, and OSC pins should
be short or shielded to prevent EMI from causing
oscillator jitter.
where f is one-half the oscillator frequency. This resis-
tance is a major component of the output impedance of
switched-capacitor circuits like the MAX1044/ICL7660.
As shown in Figure 4, the MAX1044/ICL7660 contain
MOSFET switches, the necessary transistor drive cir-
cuitry, and a timing oscillator.
Figure 2. Ideal Voltage Inverter
Figure 3a. Switched Capacitor Model
Figure 4. MAX1044 and ICL7660 Functional Diagram
Figure 3b. Equivalent Circuit
S1
V+
S2
S3 S4
C1
C2
VOUT = -(V+)
V+
C1
f
C2 RLOAD
VOUT
1M
BOOST
pin 1
OSC
pin 7
LV
pin 6
GND
pin 3
CAP-
pin 4
S2
S1
S4S3
CAP+
pin 2
V+
pin 8
VOUT
pin 5
2
Q
OSCILLATOR
INTERNAL
REGULATOR
Q
REQUIV =
REQUIV
VOUT
RLOAD
1
V+
f x C1 C2
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
7
Oscillator Frequency Considerations
For normal operation, leave the BOOST and OSC pins
of the MAX1044/ICL7660 open and use the nominal
oscillator frequency. Increasing the frequency reduces
audio interference, output resistance, voltage ripple, and
required capacitor sizes. Decreasing frequency reduces
quiescent current and improves efficiency.
Oscillator Frequency Specications
The MAX1044/ICL7660 do not have a precise oscillator
frequency. Only minimum values of 1kHz and 5kHz for the
MAX1044 and a typical value of 10kHz for the ICL7660
are specified. If a specific oscillator frequency is required,
use an external oscillator to drive the OSC pin.
Increasing Oscillator Frequency
Using the BOOST Pin
For the MAX1044, connecting the BOOST pin to the V+
pin raises the oscillator frequency by a factor of about 6.
Figure 6 shows this connection. Higher frequency opera-
tion lowers output impedance, reduces output ripple,
allows the use of smaller capacitors, and shifts switch-
ing noise out of the audio band. When the oscillator is
driven externally, BOOST has no effect and should be left
open. The BOOST pin should also be left open for normal
operation.
Reducing the Oscillator Frequency Using COSC
An external capacitor can be connected to the OSC
pin to lower the oscillator frequency (Figure 6). Lower
frequency operation improves efficiency at low load
currents by reducing the IC’s quiescent supply current.
It also increases output ripple and output impedance. This
can be offset by using larger values for C1 and C2.
Connections to the OSC pin should be short to prevent
stray capacitance from reducing the oscillator frequency.
Overdriving the OSC Pin with an
External Oscillator
Driving OSC with an external oscillator is useful when
the frequency must be synchronized, or when higher
frequencies are required to reduce audio interference.
The MAX1044/ICL7660 can be driven up to 400kHz.
The pump and output ripple frequencies are one-half the
external clock frequency. Driving the MAX1044/ICL7660
at a higher frequency increases the ripple frequency and
allows the use of smaller capacitors. It also increases the
quiescent current.
The OSC input threshold is V+ - 2.5V when V+ ≥ 5V, and
is V+ / 2 for V+ < 5V. If the external clock does not swing
all the way to V+, use a 10kΩ pull-up resistor (Figure 7).
Output Voltage Considerations
The MAX1044/ICL7660 output voltage is not regulated.
The output voltages will vary under load according to the
output resistance. The output resistance is primarily a
function of oscillator frequency and the capacitor value.
Oscillator frequency, in turn, is influenced by temperature
and supply voltage. For example, with a 5V input voltage
and 10μF charge-pump capacitors, the output resistance
is typically 50Ω. Thus, the output voltage is about -5V
under light loads, and decreases to about -4.5V with a
10mA load current.
Minor supply voltage variations that are inconsequential to
digital circuits can affect some analog circuits. Therefore,
when using the MAX1044/ICL7660 for powering sensi-
tive analog circuits, the power-supply rejection ratio of
those circuits must be considered. The output ripple and
output drop increase under heavy loads. If necessary, the
MAX1044/ICL7660 output impedance can be reduced by
paralleling devices, increasing the capacitance of C1 and
C2, or connecting the MAX1044’s BOOST pin to V+ to
increase the oscillator frequency.
Figure 5. Basic Negative Voltage Converter Figure 6. Negative Voltage Converter with COSC and BOOST
MAX1044
ICL7660
4
3
C1
10µF
*REQUIRED FOR V+ < 3.5V
VOUT = -(V+)
C2
10µF
V+
2
1
5
6
7
8
*
CBYPASS
+
MAX1044
+
4
3
10F COSC
VOUT = -(V+)
10F
V+
2
1
5
6
7
8
CONNECTION
FROM V+
TO BOOST
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
8
Inrush Current and EMI Considerations
During start-up, pump capacitors C1 and C2 must be
charged. Consequently, the MAX1044/ICL7660 develop
inrush currents during start-up. While operating, short
bursts of current are drawn from the supply to C1, and
then from C1 to C2 to replenish the charge drawn by the
load during each charge-pump cycle. If the voltage con-
verters are being powered by a high-impedance source,
the supply voltage may drop too low during the current
bursts for them to function properly. Furthermore, if the
supply or ground impedance is too high, or if the traces
between the converter IC and charge-pump capacitors
are long or have large loops, switching noise and EMI
may be generated. To reduce these effects:
1) Power the MAX1044/ICL7600 from a low-impedance
source.
2) Add a power-supply bypass capacitor with low
effective series resistance (ESR) close to the IC
between the V+ and ground pins.
3) Shorten traces between the IC and the charge-pump
capacitors.
4) Arrange the components to keep the ground pins of
the capacitors and the IC as close as possible.
5) Leave extra copper on the board around the voltage
converter as power and ground planes. This is easily
done on a double-sided PC board.
Efciency, Output Ripple,
and Output Impedance
The power efficiency of a switched-capacitor voltage
converter is affected by the internal losses in the con-
verter IC, resistive losses of the pump capacitors, and
conversion losses during charge transfer between the
capacitors. The total power loss is:
Σ P
LOSS
= P +
INTERNAL
LOSSES
P
SWITCH
LOSSES
+ +P
PUMP
CAPACITOR
LOSSES
P
CONVERSION
LOSSES
The internal losses are associated with the IC’s internal
functions such as driving the switches, oscillator, etc.
These losses are affected by operating conditions such as
input voltage, temperature, frequency, and connections to
the LV, BOOST, and OSC pins.
The next two losses are associated with the output resis-
tance of the voltage converter circuit. Switch losses occur
because of the on-resistances of the MOSFET switches
in the IC. Charge-pump capacitor losses occur because
of their ESR. The relationship between these losses and
the output resistance is as follows:
P +
PUMP
CAPACITOR
LOSSES
P
SWITCH
LOSSES
= I
OUT
2
x ROUT
where:
( )
OUT
OSC
SWITCHES SRC1 SRC2
1
Rf / 2 x C1
4(2R E ) E
≅+
++
and fOSC is the oscillator frequency.
The first term is the effective resistance from the switched-
capacitor circuit.
Conversion losses occur during the transfer of charge
between capacitors C1 and C2 when there is a voltage
difference between them. The power loss is:
()
()
22
OUT
CONV.LOSS OSC
2
RIPPLE RIPPLE
OUT
1C1 ( V ) V
2
P f /2
1C2 V 2V V
2

+− +

≅×


−


Figure 7. External Clocking
MAX1044
ICL7660
+
4
3
10µF
VOUT = -(V+)
10µF
V+
V+
CMOS or
TTL GATE
10kΩ
REQUIRED
FOR TTL
2
1
5
6
7
8
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
9
Increasing Efciency
Efficiency can be improved by lowering output voltage
ripple and output impedance. Both output voltage ripple
and output impedance can be reduced by using large
capacitors with low ESR.
The output voltage ripple can be calculated by noting that
the output current is supplied solely from capacitor C2
during one-half of the charge-pump cycle.
RIPPLET C2 OUT
OSC
1
V 2 x ESR I
2 f x C2

≅+

×

Slowing the oscillator frequency reduces quiescent
current. The oscillator frequency can be reduced by
connecting a capacitor to the OSC pin.
Reducing the oscillator frequency increases the rip-
ple voltage in the MAX1044/ICL7660. Compensate by
increasing the values of the bucket and reservoir capaci-
tors. For example, in a negative voltage converter, the
pump frequency is around 4kHz or 5kHz. With the rec-
ommended 10μF bucket and reservoir capacitors, the
circuit consumes about 70μA of quiescent current while
providing 20mA of output current. Setting the oscillator to
400Hz by connecting a 100pF capacitor to OSC reduces
the quiescent current to about 15μA. Maintaining 20mA
output current capability requires increasing the bucket
and reservoir capacitors to 100μF.
Note that lower capacitor values can be used for lower
output currents. For example, setting the oscillator to
40Hz by connecting a 1000pF capacitor to OSC provides
the highest efficiency possible. Leaving the bucket and
reservoir capacitors at 100μF gives a maximum IOUT of
2mA, a no-load quiescent current of 10μA, and a power
conversion efficiency of 98%.
General Precautions
1) Connecting any input terminal to voltages greater
than V+ or less than ground may cause latchup. Do
not apply any input sources operating from external
supplies before device power-up.
2) Never exceed maximum supply voltage ratings.
3) Do not connect C1 and C2 with the wrong polarity.
4) Do not short V+ to ground for extended periods with
supply voltages above 5.5V present on other pins.
5) Ensure that VOUT (pin 5) does not go more positive
than GND (pin 3). Adding a diode in parallel with C2,
with the anode connected to VOUT and cathode to LV,
will prevent this condition.
Application Circuits
Negative Voltage Converter
Figure 8 shows a negative voltage converter, the most
popular application of the MAX1044/ICL7660. Only two
external capacitors are needed. A third power-supply
bypass capacitor is recommended (0.1μF to 10μF)
Figure 9. Voltage Doubler
Figure 8. Negative Voltage Converter with BOOST and LV
Connections
MAX1044
ICL7660
+
4
3
C1
10µF
VOUT = -(V+)
CBYPASS
0.1µF
2
1
5
6
7
8
C2
10µF
V+
BOOST
LV
MAX1044
ICL7660
+
4
3
VOUT = 2(V+) - 2VD
2
1
5
6
7
8
C1 C2
V+
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
10
Positive Voltage Doubler
Figure 9 illustrates the recommended voltage doubler
circuit for the MAX1044/ICL7660. To reduce the volt-
age drops contributed by the diodes (VD), use Schottky
diodes. For true voltage doubling or higher output cur-
rents, use the MAX660.
Voltage Divider
The voltage divider shown in Figure 10 splits the power
supply in half. A third capacitor can be added between V+
and VOUT.
Combined Positive Multiplication and
Negative Voltage Conversion
Figure 11 illustrates this dual-function circuit. Capacitors
C1 and C3 perform the bucket and reservoir functions for
generating the negative voltage. Capacitors C2 and C4
are the bucket and reservoir capacitors for the doubled
positive voltage. This circuit has higher output imped-
ances resulting from the use of a common charge-pump
driver.
Cascading Devices
Larger negative multiples of the supply voltage can
be obtained by cascading MAX1044/ICL7660 devices
(Figure 12). The output voltage is nominally VOUT =
-n(V+) where n is the number of devices cascaded. The
output voltage is reduced slightly by the output resistance
of the first device, multiplied by the quiescent current
of the second, etc. Three or more devices can be cas-
caded in this way, but output impedance rises dramati-
cally. For example, the output resistance of two cascaded
MAX1044s is approximately five times the output resis-
tance of a single voltage converter. A better solution may
be an inductive switching regulator, such as the MAX755,
MAX759, MAX764, or MAX774.
Figure 10. Voltage Divider
Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage
Figure 11. Combined Positive and Negative Converter
MAX1044
ICL7660
+
4
3
2
1
5
6
7
8
C2
10µF
C1
10µF
V+
VOUT = V+
1
2
LV
MAX1044
ICL7660
+
4
3
2
1
5
6
7
8
MAX1044
ICL7660
4
3
2
1
5
6
7
8
10µF
10µF
10µF 10µF
V+
10µF 10µF
VOUT = -n(V+)
MAX1044
ICL7660
4
3
2
1
5
6
7
8
1 2 3
+ +
MAX1044
ICL7660
+
4
3
VOUT = 2(V+) - 2VD
2
1
5
6
7
8
C4
C1
C2
V+
VOUT = -(V+)
C3
LV
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
11
Paralleling Devices
Paralleling multiple MAX1044/ICL7660s reduces output
resistance and increases current capability. As illustrated
in Figure 13, each device requires its own pump capacitor
C1, but the reservoir capacitor C2 serves all devices. The
equation for calculating output resistance is:
OUT
OUT
R (of MAX1044 or ICL7660)
Rn (number of devices)
=
Shutdown Schemes
Figures 14a–14c illustrate three ways of adding shutdown
capability to the MAX1044/ICL7660. When using these
circuits, be aware that the additional capacitive loading
on the OSC pin will reduce the oscillator frequency. The
first circuit has the least loading on the OSC pin and has
the added advantage of controlling shutdown with a high
or low logic level, depending on the orientation of the
switching diode.
Figure 14a-14c. Shutdown Schemes for MAX1044/ICL7660
Figure 13. Paralleling MAX1044/ICL7660 to Reduce Output
Resistance
*Contact factory for dice specifications. Dice are not tested
**Contact factory for availability.
†The Maxim ICL7660 meets or exceeds all “A” and “S”
specifications.
MAX1044
ICL7660
+
4
3
VOUT = -(V+)
2
1
5
6
7
8
C2
C1
V+
MAX1044
ICL7660
4
3
2
1
5
6
7
8
C1
1
n
+
MAX1044
ICL7660
+
4
3
10µF
VOUT = -(V+)
10µF
CMOS or
TTL GATE
1N4148
V+
2
1
5
6
7
8
V+
10kΩ REQUIRED FOR TTL
74HC03
OPEN-DRAIN OR
74LS03
OPEN-COLLECTOR
NAND GATES
a)
b)
c)
V+
MAX1044
ICL7660 7
OUTPUT
ENABLE
74HC126 OR
74LS126
TRI-STATE BUFFER
V+
7
MAX1044
ICL7660
PART TEMP. RANGE PIN-PACKAGE
MAX1044CPA 0°C to +70°C 8 Plastic DIP
MAX1044CSA 0°C to +70°C 8 SO
MAX1044C/D* 0°C to +70°C Dice*
MAX1044EPA -40°C to +85°C 8 Plastic DIP
MAX1044ESA -40°C to +85°C 8 SO
MAX1044MJA -55°C to +125°C 8 CERDIP**
ICL7660CPA 0°C to +70°C 8 Plastic DIP
ICL7660CSA 0°C to +70°C 8 SO
ICL7660CUA 0°C to +70°C 8 μMAX
ICL7660C/D 0°C to +70°C Dice*
ICL7660EPA -40°C to +85°C 8 Plastic DIP
ICL7660ESA -40°C to +85°C 8 SO
ICL7660AMJA†-55°C to +125°C 8 CERDIP**
ICL7660AMTV†-55°C to +125°C 8 TO-99**
Ordering Information
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
12
Chip Topographies
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
GND CAP+ BOOST
0.076"
(1.930mm)
0.076"
(1.930mm)
CAP-
VOUT
V+
OSCLV
TRANSISTOR COUNT: 72
SUBSTRATE CONNECTED TO V+
MAX1044
GND
CAP-
LV
VOUT
TRANSISTOR COUNT: 71
SUBSTRATE CONNECTED TO V+
CAP+ 0.084"
(2.1mm)
0.060"
(1.5mm)
V+
OSC
ICL7660
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
6 TDFN-EP T633-2 21-0036 90-0058
8 Plastic DIP P8+1 21-0043 —
8 SOIC S8+2 21-0041 90-0096
8 CERDIP J8+2 21-0045 —
8 µMAX U8+1 21-0036 90-0092
8 TO-99 T99-8 21-0022 —
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
www.maximintegrated.com Maxim Integrated
│
13
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
2 2/17 Updated part numbers in Ordering Information table 13
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX1044/ICL7660 Switched-Capacitor Voltage Converters
© 2017 Maxim Integrated Products, Inc.
│
14
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Maxim Integrated:
ICL7660CSA+T ICL7660CUA+ ICL7660CUA+T ICL7660EPA+ ICL7660ESA+T ICL7660ISA+ ICL7660ISA+T
MAX1044CSA+T ICL7660AMJA/883B ICL7660ESA ICL7660ESA-T ICL7660CPA+ ICL7660CSA+ ICL7660ESA+
MAX1044CPA+ MAX1044CSA+ MAX1044ESA+ MAX1044EPA+ MAX1044ESA+T ICL7660CSA MAX1044CSA
MAX1044ESA ICL7660CPA ICL7660CSA-T ICL7660CUA ICL7660CUA-T MAX1044CSA-T MAX1044ESA-T
MAX1044MJA/883B MAX1044CPA MAX1044EPA ICL7660ISA-T ICL7660EPA ICL7660ISA