_______________General Description
The MAX1044 and ICL7660 are monolithic, CMOS
switched-capacitor voltage converters that invert, dou-
ble, 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 applica-
tions 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
o
Miniature MAX Package
o
1.5V to 10.0V Operating Supply Voltage Range
o
98% Typical Power-Conversion Efficiency
o
Invert, Double, Divide, or Multiply Input Voltages
o
BOOST Pin Increases Switching Frequencies
(MAX1044)
o
No-Load Supply Current: 200A Max at 5V
o
No External Diode Required for Higher-Voltage
Operation
______________Ordering Information
Ordering Information continued at end of data sheet.
* Contact factory for dice specifications.
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
19-4667; Rev 1; 7/94
MAX1044
ICL7660
4
3
2
1
CAP-
GND
CAP+
(N.C.) BOOST
5
6
7
8
V
OUT
LV
OSC
V+
TOP VIEW
( ) ARE FOR ICL7660
DIP/SO/MAX
TO-99
ICL7660
N.C.
CAP+
GND
CAP-
V
OUT
LV
OSC
V+ AND CASE
1
2
3
4
5
6
7
8
_________________Pin Configurations
NEGATIVE VOLTAGE CONVERTER
CAP+
CAP-
V+
V
OUT
GND
INPUT
SUPPLY
VOLTAGE
NEGATIVE
OUTPUT
VOLTAGE
MAX1044
ICL7660
__________Typical Operating Circuit
Dice*
8 SO
8 Plastic DIP
PIN-PACKAGE
TEMP. RANGE
0C to +70C
0C to +70C
0C to +70C
MAX1044C/D
MAX1044CSA
MAX1044
CPA
PART
8 Plastic DIP
-40C to +85C
MAX1044EPA
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V+ = 5.0V, LV pin = 0V, BOOST pin = open, I
LOAD
= 0mA, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
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.
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 V
OUT
) when
replacing the Intersil ICL7660. Tests are performed without diode in circuit.
Note 2:
f
OSC
is tested with C
OSC
= 100pF to minimize the effects of test fixture capacitance loading. The 1pF frequency is correlat-
ed 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).
Supply Voltage (V+ to GND, or GND to V
OUT
)....................10.5V
Input Voltage on Pins 1, 6, and 7 .........-0.3V
V
IN
(V+ + 0.3V)
LV Input Current ..................................................................20A
Output Short-Circuit Duration (V+
5.5V)..................Continuous
Continuous Power Dissipation (T
A
= +70C)
Plastic DIP (derate 9.09mW/C above +70C) ............727mW
SO (derate 5.88mW/C above +70C) .........................471mW
MAX (derate 4.1mW/C above +70C) ......................330mW
CERDIP (derate 8.00mW/C above +70C) .................640mW
TO-99 (derate 6.67mW/C above +70C) ....................533mW
Operating Temperature Ranges
MAX1044C_ _ /ICL7660C_ _ ..............................0C to +70C
MAX1044E_ _ /ICL7660E_ _ ............................-40C to +85C
MAX1044M_ _ /ICL7660M_ _ ........................-55C to +125C
Storage Temperature Range ............................-65C to + 150C
Lead Temperature (soldering, 10sec) .............................+300C
kHz
T
A
= 0C to +70C
T
A
= +25C
T
A
= -55C to +125C
V
OSC
= 0V or V+, LV open
R
L
= 5k
, T
A
= +25C, f
OSC
5kHz, LV open
T
A
= -40C to +85C
R
L
= 10k
, LV open
R
L
= 10k
, LV to GND
f
OSC
= 2.7kHz (ICL7660)
,
f
OSC
= 1kHz (MAX1044)
,
V+ = 2V, I
L
= 3mA,
LV to GND
30
200
R
L
=
,
pins 1 and 7
no connection,
LV open
A
10
Supply Current
20
Pin 1 = 0V
Pin 1 = V+
3
Oscillator Sink or
Source Current
%
95
98
Power Efficiency
C
OSC
= 1pF,
LV to GND (Note 2)
400
1
325
Output Resistance
I
L
= 20mA,
f
OSC
= 5kHz,
LV open
200
T
A
= 0C to +70C
T
A
= -40C to +85C
200
UNITS
MAX1044
MIN TYP MAX
PARAMETER
325
T
A
= +25C
130
325
130
150
200
V
1.5
10
Supply Voltage
Range (Note 1)
65
100
5
Oscillator Frequency
100
V+ = 2V
V+ = 5V
M
1.0
Oscillator Impedance
80
175
95
98
400
300
250
225
ICL7660
MIN TYP MAX
300
140
250
120
150
250
3.0
10.0
1.5
3.5
55
100
10
100
1.0
T
A
= -55C to +125C
R
L
=
, pins 1 and 7 = V+ = 3V
T
A
= +25C
T
A
= +25C
T
A
= 0C to +70C
T
A
= -40C to +85C
T
A
= -55C to +125C
V+ = 5V
V+ = 2V
R
L
=
, T
A
= +25C, LV open
99.0 99.9
%
97.0 99.9
Voltage Conversion Efficiency
A
k
CONDITIONS
80
90
100
30
10
1
EFFICIENCY
vs. OSCILLATOR FREQUENCY
70
MAX1044-Fig 7
OSCILLATOR FREQUENCY (Hz)
EFFICIENCY (%)
10
4
50
40
10
2
10
3
6x10
5
60
10
5
C1, C2 = 100F
C1, C2 = 10F
C1, C2 = 1F
EXTERNAL
HCMOS
OSCILLATOR
10,000
100,000
0.1
1
OSCILLATOR FREQUENCY
vs. EXTERNAL CAPACITANCE
1000
MAX1044-Fig 8
C
OSC
(pF)
OSCILLATOR FREQUENCY (Hz)
1000
10
1
10
100
100,000
100
10,000
ICL7660 and
MAX1044 with
BOOST = OPEN
MAX1044 with
BOOST -V+
100
1
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX1044-Fig 9
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (Hz)
4
10,000
1000
2
3
6
7
8
9
10
100,000
5
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
0
1
2
3
4
5
6
7
8
9
10
OUTPUT VOLTAGE and OUTPUT RIPPLE
vs. LOAD CURRENT
-0.5
-2.0
MAX1044-Fig 1
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
OUTPUT RIPPLE (mVp-p)
-1.5
-1.0
0
250
200
150
100
50
400
350
300
OUTPUT
VOLTAGE
V+ = 2V
LV = GND
OUTPUT RIPPLE
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
A
B
C
0
0
5
10
15
20
25
30
35
40
OUTPUT VOLTAGE and OUTPUT RIPPLE
vs. LOAD CURRENT
-0.5
-2.0
-2.5
-3.0
-3.5
-4.0
-4.5
-5.0
MAX1044-Fig 2
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
OUTPUT RIPPLE (mVp-p)
-1.5
-1.0
0
720
640
560
480
400
320
240
160
80
800
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
0
0
5
10
15
20
25
30
35
40
OUTPUT VOLTAGE and OUTPUT RIPPLE
vs. LOAD CURRENT
-1
-4
-5
-6
-7
-8
-9
-10
MAX1044-Fig 3
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
OUTPUT RIPPLE (mVp-p)
-3
-2
0
700
630
560
490
420
350
280
210
140
70
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
0
0
1
2
3
4
5
6
7
8
9 10
EFFICIENCY and SUPPLY CURRENT
vs. LOAD CURRENT
10
40
50
60
70
80
90
100
MAX1044-Fig 4
LOAD CURRENT (mA)
EFFICIENCY (%)
SUPPLY CURRENT (mA)
30
20
0
7
8
9
10
6
5
4
3
2
1
SUPPLY CURRENT
EFFICIENCY
V+ = 2V
LV = GND
0
0
5
10
15
20
25
30
35
40
EFFICIENCY and SUPPLY CURRENT
vs. LOAD CURRENT
10
40
50
60
70
80
90
100
MAX1044-Fig 5
LOAD CURRENT (mA)
EFFICIENCY (%)
SUPPLY CURRENT (mA)
30
20
0
35
40
45
50
30
25
20
15
10
5
V+ = 5V
LV = OPEN
EFFICIENCY
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
SUPPLY CURRENT
B
C
A
0
0
5
10
15
20
25
30
35
40
EFFICIENCY and SUPPLY CURRENT
vs. LOAD CURRENT
10
40
50
60
70
80
90
100
MAX1044-Fig 6
LOAD CURRENT (mA)
EFFICIENCY (%)
SUPPLY CURRENT (mA)
30
20
0
35
40
45
50
30
25
20
15
10
5
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
_______________________________________________________________________________________
3
__________________________________________Typical Operating Characteristics
(V+ = 5V; C
BYPASS
= 0.1F; C1 = C2 = 10F; LV = open; OSC = open; T
A
= +25C; unless otherwise noted.)
0.1
1
2
3
4
5
6
7
8
9
10
QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
MAX1044-Fig 12
SUPPLY VOLTAGE (V)
QUIESCENT CURRENT (A)
10
1
100
1000
2000
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
0
10
1
10
2
10
3
10
4
10
5
OUTPUT RESISTANCE
vs. OSCILLATOR FREQUENCY
MAX1044-Fig 14
FREQUENCY (Hz)
RESISTANCE (
)
200
100
300
400
500
600
700
800
900
1000
C1, C2 = 100F
C1, C2 = 1F
C1, C2 = 10F
EXTERNAL
HCMOS
OSCILLATOR
0
-50
-25
0
25
50
75
100 125
QUIESCENT CURRENT
vs. TEMPERATURE
MAX1044-Fig 13
TEMPERATURE (C)
QUIESCENT CURRENT (A)
200
100
300
400
500
ICL7660, MAX1044 with BOOST = OPEN
MAX1044 with
BOOST = V+
0
1
2
3
4
5
6
7
8
9
10
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
MAX1044-Fig 15
SUPPLY VOLTAGE (V)
OUTPUT RESISTANCE (
)
40
20
60
80
100
120
140
160
180
200
20
-60 -40 -20 0
20 40 60 80 100 120 140
OUTPUT RESISTANCE
vs. TEMPERATURE
MAX1044-Fig 16
TEMPERATURE (C)
OUTPUT RESISTANCE (
)
40
30
50
60
70
80
ICL7660,
MAX1044 with
BOOST = OPEN
MAX1044 with
BOOST = V+
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
4
_______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(V+ = 5V; C
BYPASS
= 0.1F; C1 = C2 = 10F; LV = open; OSC = open; T
A
= +25C; unless otherwise noted.)
0
-50
OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX1044-Fig 10
TEMPERATURE (C)
OSCILLATOR FREQUENCY (kHz)
25
40
20
-25
0
75
100
125
60
80
100
50
A: MAX1044 with
BOOST = V+
B: ICL7600
C: MAX1044 with
BOOST = OPEN
B
A
C
1
10
0
10
1
10
2
10
3
10
4
10
5
5x10
5
QUIESCENT CURRENT
vs. OSCILLATOR FREQUENCY
MAX1044-Fig 11
OSCILLATOR FREQUENCY (Hz)
QUIESCENT CURRENT (A)
100
10
1000
10,000
USING
EXTERNAL
HCMOS
OSCILLATOR
USING
EXTERNAL
CAPACITOR
_______________Detailed Description
The MAX1044/ICL7660 are charge-pump voltage con-
verters. 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 nega-
tive terminal to V
OUT
. 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 S1S4 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 resis-
tance (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 V
OUT
. The
charge transferred per cycle is:
Q = C1(V+ - V
OUT
). If
the switch is cycled at frequency f, then the resulting
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
_______________________________________________________________________________________
5
MAX1044
ICL7660
BOOST
CAP+
GND
C
BYPASS
= 0.1F
V+
R
L
CAP-
V+
OSC
C1
10
F
LV
V
OUT
C2
10
F
C
OSC
EXTERNAL
OSCILLATOR
V
OUT
_____________________________________________________________ Pin Description
NAME
FUNCTION
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.
PIN
1
N.C.
(ICL7660)
No Connection
3
GND
Ground. For most applications, the positive terminal of the reservoir capacitor is connected to this pin.
2
CAP+
Connection to positive terminal of Charge-Pump Capacitor
6
LV
Low-Voltage Operation. Connect to ground for supply voltages below 3.5V.
ICL7660: Leave open for supply voltages above 5V.
5
V
OUT
Negative Voltage Output. For most applications, the negative terminal of the reservoir capacitor is
connected to this pin.
4
CAP-
Connection to negative terminal of Charge-Pump Capacitor
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.
Figure 1. Maxim MAX1044/ICL7660 Test Circuit
MAX1044/ICL7660
current is: I = f x
Q = f x C1(V+ - V
OUT
). Rewriting this
equation in Ohm's law form defines an equivalent resis-
tance synthesized by the switched-capacitor circuit
where:
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.
________________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 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 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
I
(V+ - V
)
1 / (f x C1)
R
1
f x C1
OUT
EQUIV
=
=
and
Switched-Capacitor Voltage Converters
6
_______________________________________________________________________________________
S1
V+
S2
S3
S4
C1
C2
V
OUT
= -(V+)
Figure 2. Ideal Voltage Inverter
V+
C1
f
C2
R
LOAD
V
OUT
Figure 3a. Switched Capacitor Model
R
EQUIV
=
R
EQUIV
V
OUT
R
LOAD
1
V+
f
C1
C2
Figure 3b. Equivalent Circuit
1M
BOOST
pin 1
OSC
pin 7
LV
pin 6
GND
pin 3
CAP-
pin 4
S2
S1
S4
S3
CAP+
pin 2
V+
pin 8
V
OUT
pin 5
2
Q
OSCILLATOR
INTERNAL
REGULATOR
Q
Figure 4. MAX1044 and ICL7660 Functional Diagram
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 connect-
ed 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.
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 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 oper-
ation 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 C
OSC
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 10k
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
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
_______________________________________________________________________________________
7
MAX1044
ICL7660
4
3
C1
10F
*REQUIRED FOR V+ < 3.5V
V
OUT
=
-(V+)
C2
10F
V+
2
1
5
6
7
8
*
C
BYPASS
Figure 5. Basic Negative Voltage Converter
MAX1044
4
3
10F
C
OSC
V
OUT
=
-(V+)
10F
V+
2
1
5
6
7
8
CONNECTION
FROM V+
TO BOOST
Figure 6. Negative Voltage Converter with C
OSC
and BOOST
MAX1044/ICL7660
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 10F charge-pump capacitors,
the output resistance is typically 50
. 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 out-
put impedance can be reduced by paralleling devices,
increasing the capacitance of C1 and C2, or connect-
ing the MAX1044's BOOST pin to V+ to increase the
oscillator frequency.
Inrush Current and EMI Considerations
During start-up, pump capacitors C1 and C2 must be
charged. Consequently, the MAX1044/ICL7660 devel-
op 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 prop-
erly. 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.
Efficiency, 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:
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 connec-
tions 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:
where:
and f
OSC
is the oscillator frequency.
R
1
(f
/ 2) x C1
4 2R
ESR
ESR
OUT
OSC
SWITCHES
C1
C2
+
+
(
)
+
P
P
I
x R
OUT
2
OUT
+
=
P = P +P +P +P
Switched-Capacitor Voltage Converters
8
_______________________________________________________________________________________
MAX1044
ICL7660
4
3
10F
V
OUT
=
-(V+)
10F
V+
V+
CMOS or
TTL GATE
10k
REQUIRED
FOR TTL
2
1
5
6
7
8
Figure 7. External Clocking
LOSS
INTERNAL
LOSSES
SWITCH
LOSSES
PUMP
CAPACITOR
LOSSES
CONVERSION
LOSSES
PUMP
CAPACITOR
LOSSES
SWITCH
LOSSES
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:
Increasing Efficiency
Efficiency can be improved by lowering output voltage
ripple and output impedance. Both output voltage rip-
ple 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.
Slowing the oscillator frequency reduces quiescent cur-
rent. The oscillator frequency can be reduced by con-
necting 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 10F bucket and reservoir capacitors,
the circuit consumes about 70A 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 15A.
Maintaining 20mA output current capability requires
increasing the bucket and reservoir capacitors to
100F.
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 pro-
vides the highest efficiency possible. Leaving the bucket
and reservoir capacitors at 100F gives a maximum
I
OUT
of 2mA, a no-load quiescent current of 10A, 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 V
OUT
(pin 5) does not go more positive
than GND (pin 3). Adding a diode in parallel with
C2, with the anode connected to V
OUT
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 (0.1F to 10F)
V
1
2 x f
x C2
2 x ESR
I
RIPPLE
OSC
C2
OUT
+
P
1
2
C1 (V
V
1
2
C2 V
2V
V
x f
/ 2
CONV.LOSS
OUT
2
RIPPLE
2
OUT RIPPLE
OSC
)
=
+
-
+
-
2
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
_______________________________________________________________________________________
9
MAX1044
ICL7660
4
3
C1
10F
V
OUT
=
-(V+)
C
BYPASS
0.1F
2
1
5
6
7
8
C2
10F
V+
BOOST
LV
Figure 8. Negative Voltage Converter with BOOST and LV
Connections
MAX1044
ICL7660
4
3
V
OUT
= 2(V+) - 2V
D
2
1
5
6
7
8
C1
C2
V+
Figure 9. Voltage Doubler
MAX1044/ICL7660
Positive Voltage Doubler
Figure 9 illustrates the recommended voltage doubler
circuit for the MAX1044/ICL7660. To reduce the voltage
drops contributed by the diodes (V
D
), 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 V
OUT
.
Combined Positive Multiplication and
Negative Voltage Conversion
Figure 11 illustrates this dual-function circuit.
Capacitors C1 and C3 perform the bucket and reser-
voir 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 impedances 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 V
OUT
= -n(V+)
where n is the number of devices cascaded. The out-
put 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 resis-
tance of a single voltage converter. A better solution
may be an inductive switching regulator, such as the
MAX755, MAX759, MAX764, or MAX774.
Switched-Capacitor Voltage Converters
10
______________________________________________________________________________________
MAX1044
ICL7660
4
3
2
1
5
6
7
8
C2
10F
C1
10F
V+
V
OUT
= V+
1
2
LV
Figure 10. Voltage Divider
MAX1044
ICL7660
4
3
V
OUT
= 2(V+) - 2V
D
2
1
5
6
7
8
C4
C1
C2
V+
V
OUT
= -(V+)
C3
LV
Figure 11. Combined Positive and Negative Converter
MAX1044
ICL7660
4
3
2
1
5
6
7
8
MAX1044
ICL7660
4
3
2
1
5
6
7
8
10F
10F
V+
10F
10F
10F
V
OUT
= -n(V+)
10F
MAX1044
ICL7660
4
3
2
1
5
6
7
8
1
2
3
Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage
Paralleling Devices
Paralleling multiple MAX1044/ICL7660s reduces output
resistance and increases current capability. As illus-
trated 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:
Shutdown Schemes
Figures 14a14c illustrate three ways of adding shut-
down capability to the MAX1044/ICL7660. When using
these circuits, be aware that the additional capacitive
loading on the OSC pin will reduce the oscillator fre-
quency. 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.
R
R
(of MAX1044 or ICL7660)
n (number of devices)
OUT
OUT
=
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
______________________________________________________________________________________
11
MAX1044
ICL7660
4
3
V
OUT
=
-(V+)
2
1
5
6
7
8
C2
C1
V+
MAX1044
ICL7660
4
3
2
1
5
6
7
8
C1
1
n
Figure 13. Paralleling MAX1044/ICL7660 to Reduce Output
Resistance
MAX1044
ICL7660
4
3
10F
V
OUT
=
-(V+)
10F
CMOS or
TTL GATE
1N4148
V+
2
1
5
6
7
8
V+
10k
REQUIRED FOR TTL
Figure 14a-14c. Shutdown Schemes for MAX1044/ICL7660
OUTPUT
ENABLE
74HC126 OR
74LS126
TRI-STATE BUFFER
V+
7
MAX1044
ICL7660
74HC03
OPEN-DRAIN OR
74LS03
OPEN-COLLECTOR
NAND GATES
V+
MAX1044
ICL7660
7
a)
b)
c)
8 CERDIP**
8 SO
PIN-PACKAGE
TEMP. RANGE
-40C to +85C
-55C to +125C
MAX1044MJA
MAX1044ESA
PART
8 Plastic DIP
0C to +70C
ICL7660
CPA
8 SO
0C to +70C
ICL7660CSA
8 MAX
0C to +70C
ICL7660CUA
Dice*
0C to +70C
ICL7660C/D
8 Plastic DIP
-40C to +85C
ICL7660EPA
8 SO
-40C to +85C
ICL7660ESA
8 CERDIP**
-55C to +125C
ICL7660AMJA
8 TO-99**
-55C to +125C
ICL7660AMTV
_Ordering Information (continued)
* Contact factory for dice specifications.
** Contact factory for availability.
The Maxim ICL7660 meets or exceeds all "A" and "S"
specifications.
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
__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
1994 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
__________________________________________________________Chip Topographies
GND
CAP-
LV
V
OUT
TRANSISTOR COUNT: 71
SUBSTRATE CONNECTED TO V+
CAP+
0.084"
(2.1mm)
0.060"
(1.5mm)
V+
OSC
ICL7660
GND
CAP+
BOOST
0.076"
(1.930mm)
0.076"
(1.930mm)
CAP-
V
OUT
V+
OSC
LV
TRANSISTOR COUNT: 72
SUBSTRATE CONNECTED TO V+
MAX1044
L
C
A1
B
DIM
A
A1
B
C
D
E
e
H
L
MIN
0.036
0.004
0.010
0.005
0.116
0.116
0.188
0.016
0
MAX
0.044
0.008
0.014
0.007
0.120
0.120
0.198
0.026
6
MIN
0.91
0.10
0.25
0.13
2.95
2.95
4.78
0.41
0
MAX
1.11
0.20
0.36
0.18
3.05
3.05
5.03
0.66
6
INCHES
MILLIMETERS
8-PIN
MAX
PACKAGE
0.65
0.0256
21-0036
A
e
E
H
D
0.127mm
0.004 in
________________________________________________________Package Information
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