查询ICL7660供应商
19-4667; Rev 1; 7/94
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.
________________________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
__________Typical Operating Circuit
____________________________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
______________Ordering Information
PART
MAX1044CPA
MAX1044CSA
Ordering Information continued at end of data sheet.
* Contact factory for dice specifications.
0°C to +70°C
0°C to +70°C
0°C to +70°CMAX1044C/D
PIN-PACKAGETEMP. RANGE
8 Plastic DIP
8 SO
Dice*
8 Plastic DIP-40°C to +85°CMAX1044EPA
_________________Pin Configurations
TOP VIEW
(N.C.) BOOST
CAP+
GND
CAP-
1
2
MAX1044
3
4
ICL7660
8
V+
7
OSC
6
LV
5
V
OUT
MAX1044/ICL7660
N.C.
2
GND
DIP/SO/µMAX
V+ AND CASE
1
3
Maxim Integrated Products
CAP+
MAX1044
ICL7660
CAP-
GND
NEGATIVE VOLTAGE CONVERTER
________________________________________________________________
V+
V
OUT
INPUT
SUPPLY
VOLTAGE
NEGATIVE
OUTPUT
VOLTAGE
CAP+
( ) ARE FOR ICL7660
Call toll free 1-800-998-8800 for free samples or literature.
8
ICL7660
4
CAP-
TO-99
OSC
7
LV
6
V
OUT
5
1
Switched-Capacitor Voltage Converters
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V+ to GND, or GND to V
Input Voltage on Pins 1, 6, and 7.........-0.3V ≤ V
LV Input Current ..................................................................20µA
Output Short-Circuit Duration (V+ ≤ 5.5V)..................Continuous
Continuous Power Dissipation (T
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
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.
= +70°C)
A
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V+ = 5.0V, LV pin = 0V, BOOST pin = open, I
PARAMETER
MAX1044/ICL7660
RL= ∞,
pins 1 and 7
Supply Current
Supply Voltage
Range (Note 1)
Output Resistance
Oscillator Frequency
Oscillator Sink or
Source Current
Oscillator Impedance
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
replacing the Intersil ICL7660. Tests are performed without diode in circuit.
Note 2: f
is tested with C
OSC
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).
no connection,
LV open
RL= ∞, pins 1 and 7 = V+ = 3V
RL= 10kΩ, LV open
RL= 10kΩ, LV to GND
IL= 20mA,
f
OSC
LV open
f
OSC
f
OSC
V+ = 2V, IL = 3mA,
LV to GND
C
OSC
LV to GND (Note 2)
RL= 5kΩ, TA= +25°C, f
RL= ∞, TA = +25°C, LV open 99.0 99.9 %97.0 99.9Voltage Conversion Efficiency
V
OSC
TA= +25°C
= 100pF to minimize the effects of test fixture capacitance loading. The 1pF frequency is correlat-
OSC
)....................10.5V
OUT
≤ (V+ + 0.3V)
IN
CONDITIONS
= 5kHz,
= 2.7kHz (ICL7660),
= 1kHz (MAX1044),
= 1pF,
= 0V or V+, LV open
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
= 0mA, TA= T
LOAD
TA= +25°C
TA= 0°C to +70°C
TA= -40°C to +85°C
TA= -55°C to +125°C
TA= +25°C
TA= 0°C to +70°C
TA= -40°C to +85°C
TA= -55°C to +125°C
TA= +25°C
TA= 0°C to +70°C
TA= -40°C to +85°C
TA= -55°C to +125°C
V+ = 5V
V+ = 2V
5kHz, LV open
OSC
Pin 1 = 0V
Pin 1 = V+
V+ = 2V
V+ = 5V
to T
MIN
MIN TYP MAX
, unless otherwise noted.)
MAX
MAX1044
30 200
10
1.5 10
65 100
5
1
100
200
200
200
130
130
150
325
325
325
400
3
20
ICL7660
MIN TYP MAX
80 175
225
250
250
3.0 10.0
1.5 3.5
55 100
120
140
150
250
300
300
400
10
95 98
1.0
100
OUT
) when
UNITS
µA
V
Ω
kHz
%95 98Power Efficiency
µA
MΩ1.0
kΩ
2 _______________________________________________________________________________________
Switched-Capacitor Voltage Converters
__________________________________________Typical Operating Characteristics
(V+ = 5V; C
OUTPUT VOLTAGE and OUTPUT RIPPLE
-2.0
-1.5
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
-1.0
BOOST = OPEN
OUTPUT VOLTAGE (V)
-0.5
0
012345678910
EFFICIENCY and SUPPLY CURRENT
100
90
EFFICIENCY
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
012345678910
= 0.1µF; C1 = C2 = 10µF; LV = open; OSC = open; TA= +25°C; unless otherwise noted.)
BYPASS
vs. LOAD CURRENT
OUTPUT
VOLTAGE
C
B
A
OUTPUT RIPPLE
LOAD CURRENT (mA)
vs. LOAD CURRENT
SUPPLY CURRENT
LOAD CURRENT (mA)
V+ = 2V
LV = GND
V+ = 2V
LV = GND
400
350
MAX1044-Fig 1
300
250
200
150
100
50
0
10
9
MAX1044-Fig 4
8
7
6
5
4
3
2
1
0
OUTPUT VOLTAGE and OUTPUT RIPPLE
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
OUTPUT VOLTAGE (V)
OUTPUT RIPPLE (mVp-p)
-1.0
-0.5
100
90
80
70
60
50
40
EFFICIENCY (%)
30
SUPPLY CURRENT (mA)
20
10
vs. LOAD CURRENT
OUTPUT VOLTAGE
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
0
0 5 10 15 20 25 30 35 40
EFFICIENCY and SUPPLY CURRENT
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
0
0 5 10 15 20 25 30 35 40
B
A
LOAD CURRENT (mA)
vs. LOAD CURRENT
EFFICIENCY
LOAD CURRENT (mA)
C
A
B
V+ = 5V
LV = OPEN
OUTPUT RIPPLE
A
C
SUPPLY CURRENT
V+ = 5V
LV = OPEN
800
720
MAX1044-Fig 2
640
560
480
400
C
320
240
OUTPUT RIPPLE (mVp-p)
160
80
0
50
45
MAX1044-Fig 5
B
40
35
30
25
20
15
SUPPLY CURRENT (mA)
10
5
0
OUTPUT VOLTAGE and OUTPUT RIPPLE
-10
-9
-8
-7
-6
-5
-4
-3
OUTPUT VOLTAGE (V)
-2
-1
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
vs. LOAD CURRENT
C
A
V+ = 10V
LV = OPEN
SUPPLY CURRENT
OUTPUT
VOLTAGE
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
OUTPUT
RIPPLE
B
0
0
A
0 5 10 15 20 25 30 35 40
LOAD CURRENT (mA)
EFFICIENCY and SUPPLY CURRENT
vs. LOAD CURRENT
B, C
A
EFFICIENCY
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
0 5 10 15 20 25 30 35 40
LOAD CURRENT (mA)
B
C
V+ = 10V
LV = OPEN
700
630
MAX1044-Fig 3
560
490
420
350
280
210
140
70
0
50
45
MAX1044-Fig 6
40
35
30
25
20
15
10
5
0
MAX1044/ICL7660
OUTPUT RIPPLE (mVp-p)
SUPPLY CURRENT (mA)
vs. OSCILLATOR FREQUENCY
100
90
80
70
C1, C2 = 100µF
60
EFFICIENCY (%)
50
40
30
1
10
10
OSCILLATOR FREQUENCY (Hz)
EFFICIENCY
C1, C2 = 10µF
2103
C1, C2 = 1µF
EXTERNAL
HCMOS
OSCILLATOR
4
10
100,000
MAX1044-Fig 7
10,000
1000
OSCILLATOR FREQUENCY (Hz)
5
5
6x10
10
OSCILLATOR FREQUENCY
vs. EXTERNAL CAPACITANCE
ICL7660 and
100
MAX1044 with
BOOST = OPEN
10
1
0.1
1
10 100 100,000
C
MAX1044 with
BOOST -V+
1000
(pF)
OSC
10,000
100,000
MAX1044-Fig 8
10,000
1000
OSCILLATOR FREQUENCY (Hz)
100
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
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
23 678910
1
5
4
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
MAX1044-Fig 9
3
Switched-Capacitor Voltage Converters
____________________________Typical Operating Characteristics (continued)
(V+ = 5V; C
= 0.1µF; C1 = C2 = 10µF; LV = open; OSC = open; TA= +25°C; unless otherwise noted.)
BYPASS
OSCILLATOR FREQUENCY
100
80
60
40
20
OSCILLATOR FREQUENCY (kHz)
MAX1044/ICL7660
0
2000
1000
100
10
1
QUIESCENT CURRENT (µA)
0.1
vs. TEMPERATURE
A: MAX1044 with
BOOST = V+
B: ICL7600
A
B
C
-50
-25 0 75 100 125
QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
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
12345678910
C: MAX1044 with
BOOST = OPEN
25
50
TEMPERATURE (°C)
A
B
C
D
SUPPLY VOLTAGE (V)
MAX1044-Fig 10
MAX1044-Fig 12
QUIESCENT CURRENT
vs. OSCILLATOR FREQUENCY
10,000
1000
USING
100
EXTERNAL
CAPACITOR
10
QUIESCENT CURRENT (µA)
1
0101102103104105
10
500
400
300
200
100
QUIESCENT CURRENT (µA)
0
-50 -25 0 25 50 75 100 125
OSCILLATOR FREQUENCY (Hz)
QUIESCENT CURRENT
vs. TEMPERATURE
ICL7660, MAX1044 with BOOST = OPEN
TEMPERATURE (°C)
USING
EXTERNAL
HCMOS
OSCILLATOR
MAX1044 with
BOOST = V+
5x10
MAX1044-Fig 11
5
MAX1044-Fig 13
OUTPUT RESISTANCE
vs. OSCILLATOR FREQUENCY
1000
900
800
700
600
500
400
RESISTANCE (Ω)
300
C1, C2 = 100µF
200
100
0
1
10
10210310410
FREQUENCY (Hz)
C1, C2 = 10µF
EXTERNAL
HCMOS
OSCILLATOR
C1, C2 = 1µF
5
MAX1044-Fig 14
200
180
160
140
120
100
80
60
OUTPUT RESISTANCE (Ω)
40
20
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
0
12345678910
SUPPLY VOLTAGE (V)
MAX1044-Fig 15
OUTPUT RESISTANCE
80
70
60
50
40
OUTPUT RESISTANCE (Ω)
30
20
vs. TEMPERATURE
ICL7660,
MAX1044 with
BOOST = OPEN
-60 -40 -20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
4 _______________________________________________________________________________________
MAX1044 with
BOOST = V+
MAX1044-Fig 16
Switched-Capacitor Voltage Converters
_____________________________________________________________ Pin Description
NAME FUNCTION
PIN
BOOST
(MAX1044)
1
N.C.
(ICL7660)
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 V
6 LV
7 OSC
8 V+ Power-Supply Positive Voltage Input. (1.5V to 10V). V+ is also the substrate connection.
Figure 1. Maxim MAX1044/ICL7660 Test Circuit
10µF
OUT
BOOST
CAP+
C1
GND
CAP-
_______________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.
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.
No Connection
Negative Voltage Output. For most applications, the negative terminal of the reservoir capacitor is
connected to this pin.
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.
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 V
the reservoir capacitor C2. If the voltage across C2 is
. This connects C1 in parallel with
OUT
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
MAX1044
ICL7660
OSC
V+
C
V+
LV
BYPASS
= 0.1µF
EXTERNAL
OSCILLATOR
C
OSC
R
L
charge into C2 until the voltage across C2 reaches
V
OUT
10µF
C2
V
OUT
- (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 V
charge transferred per cycle is: ∆Q = C1(V+ - V
the switch is cycled at frequency f, then the resulting
OUT
. The
OUT
MAX1044/ICL7660
). If
_______________________________________________________________________________________ 5
Switched-Capacitor Voltage Converters
S1
V+
S3 S4
MAX1044/ICL7660
Figure 2. Ideal Voltage Inverter
f
V+
C1
S2
C1
C2
C2 R
V
LOAD
current is: I = f x ∆Q = f x C1(V+ - V
equation in Ohm’s law form defines an equivalent resis-
). Rewriting this
OUT
tance synthesized by the switched-capacitor circuit
where:
(V+ - V )
I
=
OUT
1 / (f x C1)
and
=
1
f x C1
R
V
= -(V+)
OUT
EQUIV
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.
________________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-
OUT
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
Figure 3a. Switched Capacitor Model
R
EQUIV
V+
1
R
=
EQUIV
f × C1
C2
Figure 3b. Equivalent Circuit
1M
V
OUT
R
LOAD
BOOST
pin 1
OSC
pin 7
÷ 2
OSCILLATOR
LV
pin 6
Q
Q
Figure 4. MAX1044 and ICL7660 Functional Diagram
INTERNAL
REGULATOR
V+
pin 8
GND
pin 3
S1
6 _______________________________________________________________________________________
CAP+
pin 2
CAP-
pin 4
S2
S4S3
V
OUT
pin 5
10µF
Switched-Capacitor Voltage Converters
MAX1044/ICL7660
CONNECTION
FROM V+
V+
1
MAX1044
C1
2
ICL7660
3
4
8
C
BYPASS
7
6
*
5
*REQUIRED FOR V+ < 3.5V
V
= -(V+)
OUT
C2
10µF
10µF
1
2
MAX1044
3
4
8
7
6
5
TO BOOST
V+
C
OSC
V
= -(V+)
OUT
10µF
Figure 5. Basic Negative Voltage Converter
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.
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. Negative Voltage Converter with C
and BOOST
OSC
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 C
An external capacitor can be connected to the OSC pin
OSC
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
_______________________________________________________________________________________ 7
Switched-Capacitor Voltage Converters
switching noise and EMI may be generated. To reduce
10kΩ
REQUIRED
V+
FOR TTL
10µF
CMOS or
V+
TTL GATE
= -(V+)
V
OUT
1
MAX1044
2
10µF
Figure 7. External Clocking
MAX1044/ICL7660
a function of oscillator frequency and the capacitor
ICL7660
3
4
8
7
6
5
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.
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 highimpedance 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,
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 converter IC, resistive losses of the pump capacitors, and
conversion losses during charge transfer between the
capacitors. The total power loss is:
∑ P = P +P +P +P
LOSS INTERNAL
LOSSES
SWITCH
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:
P P I x R
PUMP
CAPACITOR
LOSSES
+=
SWITCH
LOSSES
where:
1
(f / 2) x C1
OSC
4 2R ESR ESR
()
SWITCHES C1 C2
and f
R
≅+
OUT
is the oscillator frequency.
OSC
PUMP
CAPACITOR
LOSSES
OUT2OUT
+
+
CONVERSION
LOSSES
8 _______________________________________________________________________________________
Switched-Capacitor Voltage Converters
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:
1
P
CONV.LOSS OUT
)
C1 (V V
=+−
2
1
C2 V 2V V x f / 2
2
2
RIPPLE
2
2
−
OUT RIPPLE OSC
+
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.
V
≅+
RIPPLE
1
2 x f x C2
OSC
2 x ESR I
C2 OUT
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
I
of 2mA, a no-load quiescent current of 10µA, and
OUT
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
than GND (pin 3). Adding a diode in parallel with
C2, with the anode connected to V
to LV, will prevent this condition.
(pin 5) does not go more positive
OUT
and cathode
OUT
________________Application Circuits
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)
Negative Voltage Converter
MAX1044/ICL7660
1
BOOST
2
C1
10µF
Figure 8. Negative Voltage Converter with BOOST and LV
Connections
MAX1044
ICL7660
3
4
_______________________________________________________________________________________ 9
8
7
6
LV
5
C
BYPASS
0.1µF
C2
10µF
V+
= -(V+)
V
OUT
1
MAX1044
2
ICL7660
3
4
Figure 9. Voltage Doubler
V+
8
7
6
5
V
= 2(V+) - 2V
OUT
C1 C2
D
Switched-Capacitor Voltage Converters
1
2
MAX1044
C1
10µF
1
V
= V+
OUT
2
C2
10µF
ICL7660
3
4
8
7
6
LV
5
Figure 10. Voltage Divider
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 (VD), use Schottky
diodes. For true voltage doubling or higher output currents, 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 reservoir functions for generating the negative voltage.
Capacitors C2 and C4 are the bucket and reservoir
V+
1
2
MAX1044
ICL7660
3
C1
4
LV
C2
V+
8
7
6
5
V
OUT
V
OUT
C3
= 2(V+) - 2V
C4
= -(V+)
D
Figure 11. Combined Positive and Negative Converter
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
where n is the number of devices cascaded. The out-
OUT
= -n(V+)
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 resistance of a single voltage converter. A better solution
may be an inductive switching regulator, such as the
MAX755, MAX759, MAX764, or MAX774.
V+
8
7
10µF
6
5
10µF
1
MAX1044
2
ICL7660
3
4
8
7
10µF
6
5
10µF
1
MAX1044
2
ICL7660
3
4
10µF
1
MAX1044
2
ICL7660
3
4
123
Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage
10 ______________________________________________________________________________________
8
7
6
= -n(V+)
V
OUT
5
10µF
Switched-Capacitor Voltage Converters
1
2
MAX1044
C1
C1
ICL7660
3
4
1
2
3
4
1
MAX1044
ICL7660
n
8
7
6
5
8
7
6
5
V+
V
= -(V+)
OUT
C2
Figure 13. Paralleling MAX1044/ICL7660 to Reduce Output
Resistance
V+
10µF
10kΩ REQUIRED FOR TTL
1
MAX1044
2
ICL7660
3
4
8
1N4148
7
6
5
10µF
V+
V
OUT
CMOS or
TTL GATE
= -(V+)
a)
V+
74HC03
OPEN-DRAIN OR
MAX1044
ICL7660
7
74LS03
OPEN-COLLECTOR
NAND GATES
b)
V+
OUTPUT
ENABLE
MAX1044
ICL7660
7
74HC126 OR
74LS126
TRI-STATE BUFFER
Paralleling multiple MAX1044/ICL7660s reduces output
Paralleling Devices
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:
R (of MAX1044 or ICL7660)
R
OUT
OUT
=
n (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.
_Ordering Information (continued)
PART
MAX1044ESA
-40°C to +85°C
-55°C to +125°CMAX1044MJA
ICL7660CPA
†
†
* Contact factory for dice specifications.
** Contact factory for availability.
†
The Maxim ICL7660 meets or exceeds all “A” and “S”
specifications.
PIN-PACKAGETEMP. RANGE
8 SO
8 CERDIP**
8 Plastic DIP0°C to +70°C
8 SO0°C to +70°CICL7660CSA
8 µMAX0°C to +70°CICL7660CUA
Dice*0°C to +70°CICL7660C/D
8 Plastic DIP-40°C to +85°CICL7660EPA
8 SO-40°C to +85°CICL7660ESA
8 CERDIP**-55°C to +125°CICL7660AMJA
8 TO-99**-55°C to +125°CICL7660AMTV
MAX1044/ICL7660
c)
Figure 14a-14c. Shutdown Schemes for MAX1044/ICL7660
______________________________________________________________________________________ 11
Switched-Capacitor Voltage Converters
__________________________________________________________Chip Topographies
MAX1044
GND CAP+ BOOST
CAP-
V
OUT
MAX1044/ICL7660
0.076"
(1.930mm)
OSCLV
TRANSISTOR COUNT: 72
SUBSTRATE CONNECTED TO V+
0.076"
(1.930mm)
V+
CAP+
GND
CAP-
TRANSISTOR COUNT: 71
SUBSTRATE CONNECTED TO V+
ICL7660
0.060"
(1.5mm)
V+
(2.1mm)
OSC
LV
V
OUT
0.084"
________________________________________________________Package Information
INCHES MILLIMETERS
DIM
A
A1
B
C
E H
D
D
E
e
H
L
α
MIN
0.036
0.004
0.010
0.005
0.116
0.116
0.188
0.016
0°
MAX
MIN
0.044
0.91
0.008
0.10
0.014
0.25
0.007
0.13
0.120
2.95
0.120
2.95
4.78
0.41
0°
0.650.0256
0.198
0.026
6°
MAX
1.11
0.20
0.36
0.18
3.05
3.05
5.03
0.66
6°
21-0036
0.127mm
0.004 in
C
L
A
e
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
A1B
α
8-PIN µMAX
PACKAGE
© 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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