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MAX1044/ICL7660
Switched-Capacitor Voltage Converters
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.
●● 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
Ordering Information appears at end of data sheet.
Pin Configurations
TOP VIEW
Applications
●●
●●
●●
●●
●●
●●
●●
●●
Features
●● Miniature μMAX Package
-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
Handheld Instruments
Panel Meters
+
(N.C.) BOOST
1
CAP+
2
GND
3
CAP-
4
MAX1044
ICL7660
8
CAP+
GND
NEGATIVE VOLTAGE CONVERTER
19-4667; Rev 3; 6/19
OSC
6
LV
5
VOUT
NEGATIVE
OUTPUT
VOLTAGE
6
5
3
4
( ) ARE FOR ICL7660
OSC
7
ICL7660
2
GND
VOUT
1
INPUT
SUPPLY
VOLTAGE
MAX1044
ICL7660
CAP-
7
V+ AND CASE
N.C.
V+
V+
DIP/SO/µMAX
Typical Operating Circuit
CAP+
8
CAP-
TO-99
LV
VOUT
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Absolute Maximum Ratings
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
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
(Circuit of Figure 1, V+ = 5.0V, LV pin = 0V, BOOST pin = open, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
Supply Current
CONDITIONS
RL = ∞,
pins 1 and 7
no connection,
LV open
MAX1044
MIN
TA = +25°C
TYP
MAX
30
200
fOSC = 2.7kHz (ICL7660),
fOSC = 1kHz (MAX1044),
V+ = 2V, IL = 3mA,
LV to GND
MAX
80
175
225
TA = -40°C to +85°C
200
250
TA = -55°C to +125°C
200
250
1.5
TA = +25°C
10
65
3.0
10.0
1.5
3.5
100
55
130
120
TA = -40°C to +85°C
130
140
TA = -55°C to +125°C
150
150
TA = +25°C
325
250
TA = 0°C to +70°C
325
300
TA = -40°C to +85°C
325
300
TA = -55°C to +125°C
400
400
V+ = 5V
5
V+ = 2V
1
COSC = 1pF,
LV to GND (Note 2)
Power Efficiency
RL = 5kΩ, TA = +25°C, fOSC 5kHz, LV open
Voltage Conversion Efficiency
RL = ∞, TA = +25°C, LV open
Oscillator Sink or
Source Current
VOSC = 0V or V+,
LV open
Oscillator Impedance
TA = +25°C
µA
10
V
100
TA = 0°C to +70°C
Oscillator Frequency
UNITS
10
RL = 10kΩ, LV open
Output Resistance
TYP
200
RL = 10kΩ, LV to GND
IL = 20mA,
fOSC = 5kHz,
LV open
MIN
TA = 0°C to +70°C
RL = ∞, pins 1 and 7 = V+ = 3V
Supply Voltage
Range (Note 1)
ICL7660
Ω
kHz
95
98
95
98
%
97.0
99.9
99.0
99.9
%
Pin 1 = 0V
3
Pin 1 = V+
20
µA
V+ = 2V
1.0
1.0
MΩ
V+ = 5V
100
100
kΩ
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).
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Maxim Integrated │ 2
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Typical Operating Characteristics
(V+ = 5V; CBYPASS = 0.1μF; C1 = C2 = 10μF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)
B
2
3
5
6
7
8
9
-0.5
0
V+ = 5V
LV = OPEN
B
-1.0
0
320
C
-1.5
A
0
5
10
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
OUTPUT
RIPPLE
-3
490
420
350
280
C
V+ = 10V
LV = OPEN
B
-1
210
140
A
0
5
10
15
20
25
30
35
15
20
25
30
35
60
50
A
B
C
8
6
50
5
40
4
SUPPLY CURRENT
30
3
20
10
0
10
15
20
25
30
LOAD CURRENT (mA)
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90
40
80
15
V+ = 5V
LV = OPEN
20
10
100
45
20
SUPPLY CURRENT
30
5
50
25
35
10
40
9
7
0
30
10
60
70
35
0
70
2
V+ = 2V
LV = GND
0
1
2
3
4
5
6
7
8
9
1
10
EFFICIENCY AND SUPPLY CURRENT
vs. LOAD CURRENT
40
0
EFFICIENCY
EFFICIENCY AND SUPPLY CURRENT
vs. LOAD CURRENT
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
70
40
LOAD CURRENT (mA)
EFFICIENCY
80
40
80
OUTPUT RIPPLE
LOAD CURRENT (mA)
100
90
80
160
B, C
MAX1044-Fig 6
-4
560
EFFICIENCY (%)
-5
90
SUPPLY CURRENT (mA)
-6
100
630
240
MAX1044-Fig 4
C
700
EFFICIENCY (%)
B
OUTPUT RIPPLE (mVp-p)
A
OUTPUT
VOLTAGE
400
C
A
EFFICIENCY
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
70
60
50
40
10
0
0
50
45
40
30
25
20
SUPPLY CURRENT
30
5
0
35
15
20
10
V+ = 10V
LV = OPEN
0
5
10
15
20
25
30
35
OUTPUT RIPPLE (mVp-p)
-2.0
640
480
EFFICIENCY AND SUPPLY CURRENT
vs. LOAD CURRENT
-2
EFFICIENCY (%)
-2.5
720
560
OUTPUT VOLTAGE AND OUTPUT RIPPLE
vs. LOAD CURRENT
-7
0
10
-3.0
B
LOAD CURRENT (mA)
-8
0
4
OUTPUT RIPPLE
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
-3.5
LOAD CURRENT (mA)
-9
OUTPUT VOLTAGE (V)
1
100
50
A
0
150
V+ = 2V
LV = GND
MAX1044-Fig 3
-10
200
A
-4.0
800
SUPPLY CURRENT (mA)
0
250
C
-0.5
350
OUTPUT VOLTAGE
SUPPLY CURRENT (mA)
-1.0
-5.0
-4.5
300
A: MAX1044 WITH
BOOST = V+
B: ICL7660
C: MAX1044 WITH
BOOST = OPEN
MAX1044-Fig 5
OUTPUT VOLTAGE (V)
-1.5
400
OUTPUT VOLTAGE AND OUTPUT RIPPLE
vs. LOAD CURRENT
MAX1044-Fig 2
OUTPUT
VOLTAGE
OUTPUT VOLTAGE (V)
MAX1044-Fig 1
-2.0
OUTPUT RIPPLE (mVp-p)
OUTPUT VOLTAGE AND OUTPUT RIPPLE
vs. LOAD CURRENT
5
40
0
LOAD CURRENT (mA)
Maxim Integrated │ 3
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
OSCILLATOR FREQUENCY
vs. EXTERNAL CAPACITANCE
EFFICIENCY
vs. OSCILLATOR FREQUENCY
60
EXTERNAL
HCMOS
OSCILLATOR
50
40
30
101
102
103
104
ICL7660 AND
MAX1044 WITH
BOOST = OPEN
100
10
1
0.1
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
OSCILLATOR FREQUENCY (kHz)
MAX1044-Fig 9
OSCILLATOR FREQUENCY (Hz)
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
0
1
2
3
4
5
6
7
8
9
1000
COSC (pF)
A: MAX1044 WITH
BOOST = V+
B: ICL7600
C: MAX1044 WITH
BOOST = OPEN
80
A
60
40
20
0
10
10,000 100,000
100
OSCILLATOR FREQUENCY
vs. TEMPERATURE
100
10,000
1000
10
1
OSCILLATOR FREQUENCY (Hz)
100,000
MAX1044-Fig 8
1000
6x105
105
MAX1044 WITH
BOOST -V+
10,000
MAX1044-Fig 10
OSCILLATOR FREQUENCY (Hz)
70
C1, C2 = 1µF
80
C1, C2 = 10µF
C1, C2 = 100µF
90
EFFICIENCY (%)
100,000
MAX1044-Fig 7
100
C
-50
B
-25
0
25
50
75
100
125
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
QUIESCENT CURRENT
vs. OSCILLATOR FREQUENCY
QUIESCENT CURRENT (μA)
MAX1044-Fig 11
10,000
1000
USING
EXTERNAL
CAPACITOR
100
USING
EXTERNAL
HCMOS
OSCILLATOR
10
1
100
101
102
103
104
105 5x105
OSCILLATOR FREQUENCY (Hz)
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Maxim Integrated │ 4
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Typical Operating Characteristics (continued)
(T
unless=otherwise
(V+
5V; CBYPASS
0.1μF; C1noted.)
= C2 = 10μF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)
A = +25°C,
QUIESCENT CURRENT
vs. TEMPERATURE
QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
100
C
D
10
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
1
2
3
4
5
6
7
8
9
10
-25
200
0
25
50
75
C1, C2 = 1µF
C1, C2 = 10µF
C1, C2 = 100µF
100
125
9
10
180
700
200
160
140
120
100
80
60
40
20
100
0
-50
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
800
300
ICL7660, MAX1044 WITH BOOST = OPEN
OUTPUT RESISTANCE
vs. OSCILLATOR FREQUENCY
EXTERNAL
HCMOS
OSCILLATOR
400
100
TEMPERATURE (°C)
900
500
200
SUPPLY VOLTAGE (V)
1000
600
MAX1044 WITH
BOOST = V+
300
MAX1044-Fig 15
1
400
0
OUTPUT RESISTANCE (Ω)
0.1
MAX1044-Fig 13
QUIESCENT CURRENT (μA)
A
B
MAX1044-Fig 14
QUIESCENT CURRENT (μA)
1000
RESISTANCE (Ω)
500
1044-Fig 12
2000
101
102
103
104
0
105
1
2
50
5
6
7
8
OUTPUT RESISTANCE
vs. TEMPERATURE
70
60
4
MAX1044-Fig 16
OUTPUT RESISTANCE (Ω)
80
3
SUPPLY VOLTAGE (V)
FREQUENCY (Hz)
ICL7660,
MAX1044 WITH
BOOST = OPEN
40
MAX1044 WITH
BOOST = V+
30
20
-60 -40 -20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
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Maxim Integrated │ 5
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Pin Description
PIN
NAME
FUNCTION
BOOST
(MAX1044)
1
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.
6
LV
7
OSC
8
V+
Low-Voltage Operation. Connect to ground for supply voltages below 3.5V.
ICL7660: Leave open for supply voltages above 5V.
Oscillator Control Input. Connecting an external capacitor reduces the oscillator frequency. Minimize stray
capacitance at this pin.
Power-Supply Positive Voltage Input. (1.5V to 10V). V+ is also the substrate connection.
V+
V+
BOOST
MAX1044
ICL7660
EXTERNAL
OSCILLATOR
OSC
CAP+
C1
10µF
CBYPASS
= 0.1µF
COSC
GND
LV
CAP-
VOUT
RL
VOUT
C2
10µF
Figure 1. Maxim MAX1044/ICL7660 Test Circuit
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
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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:
I=
(V +
− VOUT )
1/ ( f x C1)
and
1
R EQUIV =
f x C1
Maxim Integrated │ 6
MAX1044/ICL7660
S2
C1
BOOST
pin 1
C2
CAP+
pin 2
S2
S4
VOUT = -(V+)
OSC
pin 7
S3
S4
Q
2
LV
pin 6
Figure 2. Ideal Voltage Inverter
Q
INTERNAL
REGULATOR
S3
V+
pin 8
S1
1M
OSCILLATOR
S1
V+
Switched-Capacitor Voltage Converters
GND
pin 3
CAPpin 4
VOUT
pin 5
Figure 4. MAX1044 and ICL7660 Functional Diagram
Design Information
f
V+
VOUT
C1
C2
RLOAD
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 components. 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 3a. Switched Capacitor Model
REQUIV
V+
1
REQUIV =
f x C1
VOUT
C2
RLOAD
Figure 3b. Equivalent Circuit
where f is one-half the oscillator frequency. This resistance 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 circuitry, and a timing oscillator.
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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 operation 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 operating 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.
Maxim Integrated │ 7
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
+
C1
10µF
2
V+
8
1
MAX1044
ICL7660
3
4
6
+
VOUT = -(V+)
1
CBYPASS
7
*
C2
10µF
5
CONNECTION
FROM V+
TO BOOST
2
10F
V+
8
MAX1044
7
3
6
4
5
COSC
VOUT = -(V+)
10F
*REQUIRED FOR V+ < 3.5V
Figure 5. Basic Negative Voltage Converter
Figure 6. Negative Voltage Converter with COSC and BOOST
Oscillator Frequency Considerations
Overdriving the OSC Pin with an
External Oscillator
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 Specifications
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 operation lowers output impedance, reduces output ripple,
allows the use of smaller capacitors, and shifts switching 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.
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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 sensitive 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.
Maxim Integrated │ 8
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
V+
10kΩ
REQUIRED
FOR TTL
+
1
2
10µF
CMOS or
V+ TTL GATE
8
MAX1044
ICL7660
7
3
6
4
5
The power efficiency of a switched-capacitor voltage
converter is affected by the internal losses in the converter IC, resistive losses of the pump capacitors, and
conversion losses during charge transfer between the
capacitors. The total power loss is:
Σ PLOSS = PINTERNAL + PSWITCH + PPUMP
LOSSES
LOSSES
VOUT = -(V+)
10µF
Figure 7. External Clocking
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 converters 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.
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Efficiency, Output Ripple,
and Output Impedance
CAPACITOR
LOSSES
+ PCONVERSION
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 resistance 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:
PPUMP
CAPACITOR
LOSSES
+ PSWITCH = IOUT2 x ROUT
LOSSES
where:
R OUT ≅
1
+
(f OSC / 2) x C1
4( 2R SWITCHES + E SRC1 ) + E SRC2
and fOSC is the oscillator frequency.
The first term is the effective resistance from the switchedcapacitor 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:
(
(
)
1
2
2
2 C1 (V + ) − VOUT +
PCONV.LOSS ≅
1 C2 V
2
RIPPLE − 2VOUT VRIPPLE
2
)
× f OSC /2
Maxim Integrated │ 9
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Increasing Efficiency
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.
1
VRIPPLET ≅
+ 2 x ESR C2 I OUT
2 × f OSC x C 2
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 ripple voltage in the MAX1044/ICL7660. Compensate by
increasing the values of the bucket and reservoir capacitors. For example, in a negative voltage converter, the
pump frequency is around 4kHz or 5kHz. With the recommended 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)
1
C1
10µF
2
V+
+
+
8
BOOST
MAX1044
ICL7660
7
3
4
V+
CBYPASS
0.1µF
6
LV
5
VOUT = -(V+)
C2
10µF
Figure 8. Negative Voltage Converter with BOOST and LV
Connections
www.maximintegrated.com
1
2
8
MAX1044
ICL7660
7
3
6
4
5
VOUT = 2(V+) - 2VD
C1
C2
Figure 9. Voltage Doubler
Maxim Integrated │ 10
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Positive Voltage Doubler
positive voltage. This circuit has higher output impedances resulting from the use of a common charge-pump
driver.
Figure 9 illustrates the recommended voltage doubler
circuit for the MAX1044/ICL7660. To reduce the voltage drops contributed by the diodes (VD), use Schottky
diodes. For true voltage doubling or higher output currents, use the MAX660.
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 cascaded in this way, but output impedance rises dramatically. For example, the output resistance of two cascaded
MAX1044s is approximately five times the output resistance of a single voltage converter. A better solution may
be an inductive switching regulator, such as the MAX755,
MAX759, MAX764, or MAX774.
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
+
1
2
C1
10µF
8
MAX1044
ICL7660
+
V+
2
7
3
LV
8
MAX1044
ICL7660
3
C1
6
4
V+
1
C3
6
LV
4
5
VOUT = -(V+)
7
5
VOUT = 2(V+) - 2VD
VOUT = 1 V+
2
C2
10µF
C2
Figure 10. Voltage Divider
Figure 11. Combined Positive and Negative Converter
+
+
1
2
10µF
V+
8
MAX1044
ICL7660
3
4
C4
7
6
1
2
10µF
5
+
1
8
MAX1044
ICL7660
3
4
7
6
2
10µF
1
2
10µF
8
MAX1044
ICL7660
3
5
4
10µF
7
6
3
5
VOUT = -n(V+)
10µF
Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage
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Maxim Integrated │ 11
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
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:
+
1
MAX1044
ICL7660
2
C1
V+
8
7
3
6
4
5
1
R OUT =
1
C1
8
MAX1044
ICL7660
7
3
VOUT = -(V+)
6
4
C2
5
n
Figure 13. Paralleling MAX1044/ICL7660 to Reduce Output
Resistance
V+
+
1
8
MAX1044
ICL7660
2
10µF
6
4
5
10kΩ REQUIRED FOR TTL
V+ CMOS or
TTL GATE
1N4148
VOUT = -(V+)
10µF
a)
V+
7
74HC03
OPEN-DRAIN OR
74LS03
OPEN-COLLECTOR
NAND GATES
b)
V+
MAX1044
7
ICL7660
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.
Ordering Information
PART
7
3
MAX1044
ICL7660
n (number of devices)
Shutdown Schemes
+
2
R OUT (of MAX1044 or ICL7660)
OUTPUT
ENABLE
74HC126 OR
74LS126
TRI-STATE BUFFER
c)
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**
*Contact factory for dice specifications. Dice are not tested.
**Contact factory for availability.
†The
Maxim ICL7660 meets or exceeds all “A” and “S”
specifications.
Figure 14a-14c. Shutdown Schemes for MAX1044/ICL7660
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Maxim Integrated │ 12
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Chip Topographies
MAX1044
GND
CAP+
ICL7660
BOOST
V+
0.076"
(1.930mm)
CAPV+
0.084"
(2.1mm)
CAP+
GND
OSC
CAPLV
VOUT
VOUT
LV
OSC
0.060"
(1.5mm)
0.076"
(1.930mm)
TRANSISTOR COUNT: 72
SUBSTRATE CONNECTED TO V+
TRANSISTOR COUNT: 71
SUBSTRATE CONNECTED TO V+
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.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
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
—
www.maximintegrated.com
Maxim Integrated │ 13
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Revision History
REVISION
NUMBER
REVISION
DATE
2
2/17
Updated part numbers in Ordering Information table
13
3
6/19
Removed TDFN-EP package information
13
DESCRIPTION
PAGES
CHANGED
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
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 specifications 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.
© 2019 Maxim Integrated Products, Inc. │ 14
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