Maxim MAX1044MJA Switched-capacitor voltage converter Datasheet

19-4667; Rev 1; 7/94
Switched-Capacitor Voltage Converters
________________________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
TEMP. RANGE
MAX1044CPA
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
MAX1044CSA
MAX1044C/D
MAX1044EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
Ordering Information continued at end of data sheet.
* Contact factory for dice specifications.
_________________Pin Configurations
TOP VIEW
(N.C.) BOOST
1
CAP+
2
GND
3
CAP-
4
MAX1044
ICL7660
8
V+
7
OSC
6
LV
5
VOUT
DIP/SO/µMAX
V+
CAP+
INPUT
SUPPLY
VOLTAGE
V+ AND CASE
8
N.C.
1
OSC
7
MAX1044
ICL7660
CAP+
CAPVOUT
NEGATIVE
OUTPUT
VOLTAGE
2
GND
GND
6
ICL7660
5
3
LV
VOUT
4
NEGATIVE VOLTAGE CONVERTER
CAP( ) ARE FOR ICL7660
TO-99
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
MAX1044/ICL7660
_______________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.
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 TYP MAX
ICL7660
MIN TYP MAX
30
80
TA = +25°C
175
TA = 0°C to +70°C
200
225
TA = -40°C to +85°C
200
250
TA = -55°C to +125°C
200
250
RL = ∞, pins 1 and 7 = V+ = 3V
Supply Voltage
Range (Note 1)
200
1.5
TA = +25°C
10
65
IL = 20mA,
fOSC = 5kHz,
LV open
TA = 0°C to +70°C
TA = -40°C to +85°C
TA = -55°C to +125°C
Output Resistance
fOSC = 2.7kHz (ICL7660), TA = +25°C
fOSC = 1kHz (MAX1044), TA = 0°C to +70°C
V+ = 2V, IL = 3mA,
TA = -40°C to +85°C
LV to GND
TA = -55°C to +125°C
V+ = 5V
COSC = 1pF,
Oscillator Frequency
LV to GND (Note 2)
V+ = 2V
Power Efficiency
RL = 5kΩ, TA = +25°C, fOSC 5kHz, LV open
Voltage Conversion Efficiency RL = ∞, TA = +25°C, LV open
Pin 1 = 0V
Oscillator Sink or
VOSC = 0V or V+, LV open
Source Current
Pin 1 = V+
V+ = 2V
Oscillator Impedance
TA = +25°C
V+ = 5V
µA
10
RL = 10kΩ, LV open
RL = 10kΩ, LV to GND
UNITS
3.0
10.0
1.5
3.5
100
55
130
130
150
325
325
325
400
5
1
95 98
97.0 99.9
100
120
140
150
250
300
300
400
10
95 98
99.0 99.9
3
20
1.0
100
V
Ω
kHz
%
%
µA
1.0
100
MΩ
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).
2
_______________________________________________________________________________________
Switched-Capacitor Voltage Converters
150
C
V+ = 2V
LV = GND
-0.5
100
50
OUTPUT RIPPLE
0
0
1
2
3
4
5
6
7
8
9
480
400
C
320
-2.0
C
-1.5
V+ = 5V
LV = OPEN
B
240
-0.5
A
0
OUTPUT RIPPLE
0
10
0
5
10
15
20
25
30
35
C
-6
-5
490
420
350
280
-4
OUTPUT
RIPPLE
-3
160
-2
80
-1
0
0
C
V+ = 10V
LV = OPEN
70
0
0
40
5
10
15
20
25
30
35
50
5
40
SUPPLY CURRENT
4
60
50
3
20
2
20
1
0
V+ = 2V
LV = GND
0
1
2
3
4
5
6
7
8
V+ = 5V
LV = OPEN
0
0
0
5
10
15
20
25
30
35
MAX1044-Fig 7
EXTERNAL
HCMOS
OSCILLATOR
50
40
MAX1044 with
BOOST -V+
102
103
104
105
OSCILLATOR FREQUENCY (Hz)
6x105
ICL7660 and
MAX1044 with
BOOST = OPEN
10
1
10
100
1000
COSC (pF)
MAX1044-Fig 6
15
10
V+ = 10V
LV = OPEN
5
0
5
10
15
20
25
30
35
40
100,000
10,000
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
1000
100
1
20
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
0.1
101
25
SUPPLY CURRENT
0
1000
100
30
LOAD CURRENT (mA)
100,000
10,000
40
45
35
30
10
OSCILLATOR FREQUENCY
vs. EXTERNAL CAPACITANCE
60
40
5
50
40
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
50
10
0
A
EFFICIENCY
60
20
EFFICIENCY
vs. OSCILLATOR FREQUENCY
C1, C2 = 1µF
70
20
15
LOAD CURRENT (mA)
C1, C2 = 10µF
80
SUPPLY CURRENT
LOAD CURRENT (mA)
C1, C2 = 100µF
90
25
B, C
70
10
9 10
100
80
35
30
OSCILLATOR FREQUENCY (Hz)
0
40
30
40
30
10
C
90
40
MAX1044-Fig 9
6
70
100
45
EFFICIENCY (%)
60
B
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
50
SUPPLY CURRENT (mA)
7
A
EFFICIENCY
OSCILLATOR FREQUENCY (Hz)
70
MAX1044-Fig 5
80
EFFICIENCY (%)
8
SUPPLY CURRENT (mA)
MAX1044-Fig 4
EFFICIENCY
90
140
A
EFFICIENCY and SUPPLY CURRENT
vs. LOAD CURRENT
100
210
B
EFFICIENCY and SUPPLY CURRENT
vs. LOAD CURRENT
9
630
560
EFFICIENCY and SUPPLY CURRENT
vs. LOAD CURRENT
10
700
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
-7
LOAD CURRENT (mA)
80
EFFICIENCY (%)
560
-8
B
LOAD CURRENT (mA)
90
30
B
A
OUTPUT
VOLTAGE
LOAD CURRENT (mA)
100
EFFICIENCY (%)
-2.5
-1.0
B
A
-3.0
-9
640
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
-3.5
-10
720
OUTPUT RIPPLE (mVp-p)
200
-4.0
800
MAX1044-Fig 8
-1.0
250
A
SUPPLY CURRENT (mA)
300
A: MAX1044 with
BOOST = V+
B: ICL7660
C: MAX1044 with
BOOST = OPEN
OUTPUT VOLTAGE
OUTPUT VOLTAGE (V)
-4.5
OUTPUT RIPPLE (mVp-p)
-5.0
350
MAX1044-Fig 2
MAX1044-Fig 1
-1.5
400
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
OUTPUT
VOLTAGE
OUTPUT RIPPLE (mVp-p)
-2.0
OUTPUT VOLTAGE and OUTPUT RIPPLE
vs. LOAD CURRENT
OUTPUT VOLTAGE and OUTPUT RIPPLE
vs. LOAD CURRENT
MAX1044-Fig 3
OUTPUT VOLTAGE and OUTPUT RIPPLE
vs. LOAD CURRENT
10,000 100,000
1
2
3
4
5
6
7
8
9
10
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
MAX1044/ICL7660
__________________________________________Typical Operating Characteristics
(V+ = 5V; CBYPASS = 0.1µF; C1 = C2 = 10µF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)
____________________________Typical Operating Characteristics (continued)
(V+ = 5V; CBYPASS = 0.1µF; C1 = C2 = 10µF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)
OSCILLATOR FREQUENCY
vs. TEMPERATURE
QUIESCENT CURRENT
vs. OSCILLATOR FREQUENCY
A
60
40
20
-25
0
25
50
75
MAX1044-Fig 11
USING
EXTERNAL
HCMOS
OSCILLATOR
10
1
100
D
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
4
5
6
7
8
9
MAX1044 with
BOOST = V+
300
200
100
ICL7660, MAX1044 with BOOST = OPEN
0
-50
10
OUTPUT RESISTANCE (Ω)
140
120
100
80
60
100
20
103
104
105
100 125
70
60
ICL7660,
MAX1044 with
BOOST = OPEN
50
40
MAX1044 with
BOOST = V+
30
0
102
75
80
MAX1044-Fig 15
MAX1044-Fig 14
160
40
FREQUENCY (Hz)
4
180
200
0
101
50
OUTPUT RESISTANCE
vs. TEMPERATURE
200
OUTPUT RESISTANCE (Ω)
300
C1, C2 = 1µF
400
C1, C2 = 10µF
500
C1, C2 = 100µF
700
600
25
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
OUTPUT RESISTANCE
vs. OSCILLATOR FREQUENCY
EXTERNAL
HCMOS
OSCILLATOR
0
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
1000
-25
MAX1044-Fig 16
3
MAX1044-Fig 13
MAX1044-Fig 12
400
10
800
105 5x105
500
C
900
104
QUIESCENT CURRENT
vs. TEMPERATURE
100
2
103
QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
A
B
0.1
102
OSCILLATOR FREQUENCY (Hz)
1000
1
101
TEMPERATURE (°C)
2000
1
USING
EXTERNAL
CAPACITOR
100
100 125
QUIESCENT CURRENT (µA)
C
1000
B
0
-50
QUIESCENT CURRENT (µA)
QUIESCENT CURRENT (µA)
A: MAX1044 with
BOOST = V+
B: ICL7600
C: MAX1044 with
BOOST = OPEN
80
10,000
MAX1044-Fig 10
OSCILLATOR FREQUENCY (kHz)
100
RESISTANCE (Ω)
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
1
2
3
4
5
6
7
SUPPLY VOLTAGE (V)
8
9
10
20
-60 -40 -20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
_______________________________________________________________________________________
Switched-Capacitor Voltage Converters
PIN
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.
N.C.
(ICL7660)
No Connection
1
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
CAP+ ICL7660
CBYPASS
= 0.1µF
EXTERNAL
OSCILLATOR
OSC
COSC
C1
10µF
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 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: ∆Q = C1(V+ - VOUT). If
the switch is cycled at frequency f, then the resulting
_______________________________________________________________________________________
5
MAX1044/ICL7660
_____________________________________________________________ Pin Description
S1
current is: I = f x ∆Q = f x C1(V+ - VOUT). Rewriting this
equation in Ohm’s law form defines an equivalent resistance synthesized by the switched-capacitor circuit
where:
S2
V+
(V+ - VOUT )
1 / (f x C1)
and
1
REQUIV =
f x C1
I=
C1
S3
C2
S4
VOUT = -(V+)
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.
Figure 2. Ideal Voltage Inverter
________________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 lowpower 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
VOUT
1
f × C1
BOOST
pin 1
OSC
pin 7
C2
6
S3
S4
Q
RLOAD
LV
pin 6
Figure 3b. Equivalent Circuit
CAP+
pin 2
S2
Q
÷2
INTERNAL
REGULATOR
V+
REQUIV =
V+
pin 8
S1
1M
REQUIV
OSCILLATOR
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
GND
pin 3
CAPpin 4
Figure 4. MAX1044 and ICL7660 Functional Diagram
_______________________________________________________________________________________
VOUT
pin 5
Switched-Capacitor Voltage Converters
C1
10µF
2
3
4
V+
8
1
MAX1044
ICL7660
7
6
VOUT = -(V+)
1
V+
8
CBYPASS
*
C2
10µF
2
MAX1044
7
10µF
3
COSC
6
VOUT = -(V+)
5
4
5
10µF
*REQUIRED FOR V+ < 3.5V
Figure 5. Basic Negative Voltage Converter
Figure 6. Negative Voltage Converter with COSC and BOOST
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.
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.
Oscillator Frequency Considerations
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.
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.
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).
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.
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
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.
Output Voltage Considerations
_______________________________________________________________________________________
7
MAX1044/ICL7660
CONNECTION
FROM V+
TO BOOST
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
V+
1
2
10µF
10kΩ
REQUIRED
FOR TTL
CMOS or
V+ TTL GATE
8
MAX1044
ICL7660
7
3
6
4
5
VOUT = -(V+)
10µF
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.
Figure 7. External Clocking
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.
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,
8
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:
∑ PLOSS = PINTERNAL +PSWITCH +PPUMP
LOSSES
LOSSES
+PCONVERSION
CAPACITOR
LOSSES
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:
2
+ PSWITCH = IOUT x ROUT
PPUMP
CAPACITOR
LOSSES
LOSSES
where:
ROUT ≅
1
+
(fOSC / 2) x C1
(
)
4 2RSWITCHES + ESRC1 + ESRC2
and fOSC is the oscillator frequency.
_______________________________________________________________________________________
Switched-Capacitor Voltage Converters
1
2
PCONV.LOSS =  C1  (V+ ) 2 − VOUT  +


2

1
2
C2  VRIPPLE − 2VOUT VRIPPLE   x fOSC / 2


2
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
VRIPPLE ≅ 
+ 2 x ESRC2  IOUT
 2 x fOSC x C2

Slowing the oscillator frequency reduces quiescent current. The oscillator frequency can be reduced by connecting a capacitor to the OSC pin.
Reducing the oscillator frequency increases the 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)
V+
1
1
2
C1
10µF
8
BOOST
7
MAX1044
ICL7660
3
4
8
V+
CBYPASS
0.1µF
2
MAX1044
ICL7660
7
3
6
4
5
VOUT = 2(V+) - 2VD
6
LV
VOUT = -(V+)
5
C1
C2
C2
10µF
Figure 8. Negative Voltage Converter with BOOST and LV
Connections
Figure 9. Voltage Doubler
_______________________________________________________________________________________
9
MAX1044/ICL7660
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:
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
V+
V+
C1
10µF
1
8
1
2
7
2
3
MAX1044
ICL7660
LV
4
C3
LV
4
5
VOUT = -(V+)
7
MAX1044
ICL7660
3
C1
6
8
6
5
VOUT = 2(V+) - 2VD
VOUT = 1 V+
2
C2
10µF
C2
Figure 10. Voltage Divider
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.
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 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
1
2
10µF
4
V+
8
MAX1044
ICL7660
3
7
6
1
C4
1
2
10µF
5
8
MAX1044
ICL7660
3
4
7
6
2
10µF
1
2
10µF
8
MAX1044
ICL7660
3
5
4
6
3
10µF
Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage
10
7
______________________________________________________________________________________
5
VOUT = -n(V+)
10µF
Switched-Capacitor Voltage Converters
1
2
C1
V+
8
7
MAX1044
ICL7660
3
6
4
ROUT =
5
ROUT (of MAX1044 or ICL7660)
n (number of devices)
1
Shutdown Schemes
1
8
2
C1
7
MAX1044
ICL7660
3
VOUT = -(V+)
6
4
C2
5
n
Figures 14a–14c illustrate three ways of adding shutdown capability to the MAX1044/ICL7660. When using
these circuits, be aware that the additional capacitive
loading on the OSC pin will reduce the oscillator frequency. The first circuit has the least loading on the
OSC pin and has the added advantage of controlling
shutdown with a high or low logic level, depending on
the orientation of the switching diode.
Figure 13. Paralleling MAX1044/ICL7660 to Reduce Output
Resistance
V+
1
_Ordering Information (continued)
10kΩ REQUIRED FOR TTL
V+ CMOS or
8
TTL GATE
1N4148
2
10µF
MAX1044
ICL7660
7
3
6
4
5
VOUT = -(V+)
10µF
a)
V+
MAX1044
ICL7660
7
74HC03
OPEN-DRAIN OR
74LS03
OPEN-COLLECTOR
NAND GATES
PART
TEMP. RANGE
MAX1044ESA
MAX1044MJA
ICL7660CPA
ICL7660CSA
ICL7660CUA
ICL7660C/D
ICL7660EPA
ICL7660ESA
ICL7660AMJA†
ICL7660AMTV†
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
-55°C to +125°C
PIN-PACKAGE
8 SO
8 CERDIP**
8 Plastic DIP
8 SO
8 µMAX
Dice*
8 Plastic DIP
8 SO
8 CERDIP**
8 TO-99**
* Contact factory for dice specifications.
** Contact factory for availability.
† The Maxim ICL7660 meets or exceeds all “A” and “S”
specifications.
b)
V+
MAX1044
ICL7660
7
OUTPUT
ENABLE
74HC126 OR
74LS126
TRI-STATE BUFFER
c)
Figure 14a-14c. Shutdown Schemes for MAX1044/ICL7660
______________________________________________________________________________________
11
MAX1044/ICL7660
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:
MAX1044/ICL7660
Switched-Capacitor Voltage Converters
__________________________________________________________Chip Topographies
MAX1044
GND
CAP+
ICL7660
BOOST
V+
0.084"
(2.1mm)
CAP+
0.076"
(1.930mm)
GND
OSC
CAPCAPV+
LV
V OUT
V OUT
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
DIM
E
A
A1
B
C
D
E
e
H
L
α
H
INCHES
MAX
MIN
0.044
0.036
0.008
0.004
0.014
0.010
0.007
0.005
0.120
0.116
0.120
0.116
0.0256
0.198
0.188
0.026
0.016
6°
0°
MILLIMETERS
MIN
MAX
0.91
1.11
0.10
0.20
0.25
0.36
0.13
0.18
2.95
3.05
2.95
3.05
0.65
4.78
5.03
0.41
0.66
0°
6°
21-0036
D
C
α
A
0.127mm
0.004 in
e
B
A1
8-PIN µMAX
PACKAGE
L
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.