1
TM
File Number 3072.4
ICL7660, ICL7660A
CMOS Voltage Converters
The Intersil ICL7660 and ICL7660A are monolithic CMOS
power supply circuits which offer unique performance
advantages over previously available devices. The ICL7660
performs supply voltage conversions from positive to
negative for an input range of +1.5V to +10.0V resulting in
complementary output voltages of -1.5V to -10.0V and the
ICL7660A does the same conversions with an inputrange of
+1.5V to +12.0V resulting in complementary output voltages
of -1.5V to -12.0V. Only 2 noncritical external capacitors are
needed for the charge pump and charge reservoir functions.
The ICL7660 and ICL7660A can also be connected to
function as voltage doublers and will generate output
voltages up to +18.6V with a +10V input.
Contained on the chip are a series DC supply regulator, RC
oscillator, voltage level translator, and four output power
MOS switches. A unique logic element senses the most
negative voltage in the device and ensures that the output N-
Channel switch source-substrate junctions are not forward
biased. This assures latchup free operation.
The oscillator, when unloaded, oscillates at a nominal
frequency of 10kHz for an input supply voltage of 5.0V. This
frequency can be lowered by the addition of an external
capacitor to the “OSC” terminal, or the oscillator may be
overdriven by an external clock.
The “LV” terminal may be tied to GROUND to bypass the
internal series regulator and improve low voltage (LV)
operation. At medium to high voltages (+3.5V to +10.0V for
the ICL7660 and +3.5V to +12.0V for the ICL7660A), the LV
pin is left floating to prevent device latchup.
Features
• Simple Conversion of +5V Logic Supply to ±5V Supplies
• Simple Voltage Multiplication (VOUT =(-)nV
IN)
• Typical Open Circuit Voltage Conversion Efficiency 99.9%
• Typical Power Efficiency 98%
• Wide Operating Voltage Range
- ICL7660 ..........................1.5Vto10.0V
- ICL7660A . . . ......................1.5Vto12.0V
• ICL7660A 100% Tested at 3V
• Easy to Use - Requires Only 2 External Non-Critical
Passive Components
• No External Diode Over Full Temp. and Voltage Range
Applications
• On Board Negative Supply for Dynamic RAMs
• Localized µProcessor (8080 Type) Negative Supplies
• Inexpensive Negative Supplies
• Data Acquisition Systems
Pinouts
ICL7660, ICL7660A (PDIP, SOIC)
TOP VIEW
ICL7660 (METAL CAN)
TOP VIEW
Ordering Information
PART NO. TEMP.
RANGE (oC) PACKAGE PKG.
NO.
ICL7660CBA 0 to 70 8 Ld SOIC (N) M8.15
ICL7660CBA-T 0 to 70 8 Ld SOIC (N)
Tape and Reel M8.15
ICL7660CPA 0 to 70 8 Ld PDIP E8.3
ICL7660MTV†0to70 8PinMetalCan T8.C
ICL7660ACBA 0 to 70 8 Ld SOIC (N) M8.15
ICL7660ACBA-T 0 to 70 8 Ld SOIC (N)
Tape and Reel M8.15
ICL7660ACPA 0 to 70 8 Ld PDIP E8.3
ICL7660AIBA -40 to 85 8 Ld SOIC (N) M8.15
ICL7660AIBA-T -40 to 85 8 Ld SOIC (N)
Tape and Reel M8.15
ICL7660AIPA -40 to 85 8 Ld PDIP E8.3
†Add /883B to part number if 883B processing is required.
NC
CAP+
GND
CAP-
1
2
3
4
8
7
6
5
V+
OSC
LV
VOUT
V+ (AND CASE)
LV
CAP+
NC
GND
OSC
VOUT
2
4
6
1
3
7
5
8
CAP-
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CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 |Intersil and Design is a trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2001, All Rights Reserved
2
C
Absolute Maximum Ratings Thermal Information
Supply Voltage
ICL7660.......................................+10.5V
ICL7660A......................................+13.0V
LV and OSC Input Voltage. . . . . . -0.3V to (V+ +0.3V) for V+ < 5.5V
(Note2) ..............(V+-5.5V)to(V++0.3V)forV+>5.5V
CurrentintoLV(Note2)...................20µAforV+>3.5V
Output Short Duration (VSUPPLY ≤ 5.5V) ............Continuous
Operating Conditions
Temperature Range
ICL7660M...............................-55
oCto125
oC
ICL7660C,ICL7660AC........................0
oCto70
oC
ICL7660AI ...............................-40
oCto85
oC
Thermal Resistance (Typical, Note 1) θJA (oC/W) θJC (oC/W)
PDIPPackage................... 150 N/A
SOICPackage................... 165 N/A
Metal Can Package (ICL7660 Only) . . 160 70
MaximumStorageTemperatureRange.......... -65
oCto150
oC
MaximumLeadTemperature(Soldering,10s).............300
oC
(SOIC - Lead Tips Only)
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operationofthe
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE:
1. θJA is measured with the component mounted on an evaluation PC board in free air.
Electrical Specifications ICL7660 and ICL7660A, V+ = 5V, TA=25
oC, COSC = 0, Test Circuit Figure 11
Unless Otherwise Specified
PARAMETER SYMBOL TEST CONDITIONS
ICL7660 ICL7660A
UNITSMIN TYP MAX MIN TYP MAX
Supply Current I+ RL=∞- 170 500 - 80 165 µA
Supply Voltage Range - Lo VL+MIN≤TA≤MAX, RL=10kΩ, LV to GND 1.5 - 3.5 1.5 - 3.5 V
Supply Voltage Range - Hi VH+MIN≤TA≤MAX, RL=10kΩ,LVtoOpen 3.0 - 10.0 3 - 12 V
Output Source Resistance ROUT IOUT =20mA,T
A=25
oC - 55 100 - 60 100 Ω
IOUT =20mA,0
oC≤TA≤70oC--120--120Ω
IOUT =20mA,-55
oC≤TA≤125oC --150---Ω
IOUT =20mA,-40
oC≤TA≤85oC -----120Ω
V+=2V,I
OUT =3mA,LVtoGND
0oC≤TA≤70oC--300--300Ω
V+=2V,I
OUT = 3mA, LV to GND,
-55oC≤TA≤125oC--400--- Ω
Oscillator Frequency fOSC -10- -10-kHz
Power Efficiency PEF RL=5kΩ95 98 - 96 98 - %
Voltage Conversion Efficiency VOUT EF RL=∞97 99.9 - 99 99.9 - %
Oscillator Impedance ZOSC V+=2V - 1.0 - - 1 - MΩ
V=5V -100----kΩ
ICL7660A, V+ = 3V, TA=25
oC, OSC = Free running, Test Circuit Figure 11, Unless Otherwise Specified
Supply Current (Note 3) I+ V+ = 3V, RL=∞,25
oC - - - - 26 100 µA
0oC<T
A<70
oC -----125µA
-40oC<T
A<85
oC -----125µA
Output Source Resistance ROUT V+=3V,I
OUT = 10mA - - - - 97 150 Ω
0oC<T
A<70
oC -----200Ω
-40oC<T
A<85
oC -----200Ω
Oscillator Frequency (Note 3) fOSC V+ = 3V (same as 5V conditions) - - - 5.0 8 - kHz
0oC<T
A<70
oC---3.0--kHz
-40oC<T
A<85
oC---3.0--kHz
ICL7660, ICL7660A
3
Functional Block Diagram
Voltage Conversion Efficiency VOUTEFF V+=3V,R
L=∞---99--%
TMIN <T
A<T
MAX ---99--%
Power Efficiency PEFF V+=3V,R
L=5kΩ---96--%
TMIN <T
A<T
MAX ---95--%
NOTES:
2. Connecting any input terminal to voltages greater than V+ or less than GND may cause destructive latchup. It is recommended that no inputs
from sources operating from external supplies be applied prior to “power up” of the ICL7660, ICL7660A.
3. Derate linearly above 50oCby5.5mW/
oC.
4. In the test circuit, there is no external capacitor applied to pin 7. However, when the device is plugged into a test socket, there is usuallya very
small but finite stray capacitance present, of the order of 5pF.
5. The Intersil ICL7660A can operate without an external diode over the full temperature and voltage range. This device will function in existing
designs which incorporate an external diode with no degradation in overall circuit performance.
Electrical Specifications ICL7660 and ICL7660A, V+ = 5V, TA=25
oC, COSC = 0, Test Circuit Figure 11
Unless Otherwise Specified (Continued)
PARAMETER SYMBOL TEST CONDITIONS
ICL7660 ICL7660A
UNITSMIN TYP MAX MIN TYP MAX
RC
OSCILLATOR ÷2VOLTAGE
LEVEL
TRANSLATOR
VOLTAGE
REGULATOR LOGIC
NETWORK
OSC LV
V+
CAP+
CAP-
VOUT
Typical Performance Curves (Test Circuit of Figure 11)
FIGURE 1. OPERATING VOLTAGE AS A FUNCTION OF
TEMPERATURE FIGURE 2. OUTPUT SOURCE RESISTANCE AS A FUNCTION
OF SUPPLY VOLTAGE
10
SUPPLY VOLTAGE RANGE
(NO DIODE REQUIRED)
8
6
4
2
0-55 -25 0 25 50 100 125
TEMPERATURE (oC)
SUPPLY VOLTAGE (V)
10K
TA=25
oC
1000
100
1001 2345678
SUPPLY VOLTAGE (V+)
OUTPUT SOURCE RESISTANCE (Ω)
ICL7660, ICL7660A
4
FIGURE 3. OUTPUT SOURCE RESISTANCE AS A FUNCTION
OF TEMPERATURE FIGURE 4. POWER CONVERSION EFFICIENCY AS A
FUNCTION OF OSC. FREQUENCY
FIGURE 5. FREQUENCY OF OSCILLATION AS A FUNCTION
OF EXTERNAL OSC. CAPACITANCE FIGURE 6. UNLOADED OSCILLATOR FREQUENCY AS A
FUNCTION OF TEMPERATURE
FIGURE 7. OUTPUT VOLTAGE AS AFUNCTION OFOUTPUT
CURRENT FIGURE 8. SUPPLY CURRENT AND POWER CONVERSION
EFFICIENCY AS A FUNCTION OF LOAD
CURRENT
Typical Performance Curves (Test Circuit of Figure 11) (Continued)
350
300
250
200
150
100
50
0
-55 -25 0 25 50 75 100 125
TEMPERATURE (oC)
OUTPUT SOURCE RESISTANCE (Ω)
IOUT =1mA
V+=+2V
V+=5V
POWER CONVERSION EFFICIENCY (%)
TA=25
oC
IOUT =1mA
IOUT =15mA
100
98
96
94
92
90
88
86
84
82
80100 1K 10K
OSC. FREQUENCY fOSC (Hz)
V+=+5V
OSCILLATOR FREQUENCY fOSC (Hz)
10K
1K
100
10
V+ = 5V
TA=25
oC
1.0 10 100 1000 10K
COSC (pF)
20
18
16
14
12
10
8
6-50 -25 0 25 50 75 100 125
OSCILLATOR FREQUENCY fOSC (kHz)
TEMPERATURE (oC)
V+=+5V
TA=25
oC
V+=+5V
5
4
3
2
1
0
-1
-2
-3
-4
-5
OUTPUT VOLTAGE
LOAD CURRENT IL(mA)
SLOPE 55Ω
0 1020304050607080
PEFF I+
TA=25
oC
V+=+5V
SUPPLY CURRENT I+ (mA)
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
00 102030405060
POWER CONVERSION EFFICIENCY (%)
LOAD CURRENT IL(mA)
ICL7660, ICL7660A
5
Detailed Description
The ICL7660 and ICL7660A contain all the necessary
circuitry to complete a negative voltage converter, with the
exception of 2 external capacitors which may be inexpensive
10µF polarized electrolytic types. The mode of operation of
the device may be best understood by considering Figure
12, which shows an idealized negative voltage converter.
Capacitor C1is charged to a voltage, V+, for the half cycle
when switches S1and S3are closed. (Note: Switches S2
and S4are open during this half cycle.) During the second
half cycle of operation, switches S2and S4are closed, with
S1and S3open, thereby shifting capacitor C1negatively by
V+ volts. Charge is then transferred from C1to C2such that
the voltage on C2is exactly V+, assuming ideal switches and
no load on C2. The ICL7660 approaches this ideal situation
more closely than existing non-mechanical circuits.
In the ICL7660 and ICL7660A, the 4 switches of Figure 12
are MOS power switches; S1is a P-Channel device and S2,
S3and S4are N-Channel devices. The main difficulty with
this approach is that in integrating the switches, the
substrates of S3and S4must always remain reverse biased
with respect to their sources, but not so much as to degrade
their “ON” resistances. In addition, at circuit start-up, and
under output short circuit conditions (VOUT = V+), the output
voltage must be sensed and the substrate bias adjusted
accordingly. Failure to accomplish this would result in high
power losses and probable device latchup.
This problem is eliminated in the ICL7660 and ICL7660A by a
logic network which senses the output voltage (VOUT) together
with the level translators,and switches the substratesof S3and
S4to the correct level to maintain necessary reverse bias.
FIGURE 9. OUTPUT VOLTAGE AS AFUNCTION OFOUTPUT
CURRENT FIGURE 10. SUPPLY CURRENT AND POWER CONVERSION
EFFICIENCY AS A FUNCTION OF LOAD
CURRENT
NOTE:
6. These curves include in the supply current that current fed directly into the load RLfrom the V+ (See Figure 11). Thus, approximately half the
supply current goes directly to the positive side of the load, and the other half, through the ICL7660/ICL7660A, to the negative side of the load.
Ideally, VOUT ∼ 2VIN,I
S∼2IL,soV
IN xI
S∼VOUT xI
L.
NOTE: For large values of COSC (>1000pF) the values of C1and C2 should be increased to 100µF.
FIGURE 11. ICL7660, ICL7660A TEST CIRCUIT
Typical Performance Curves (Test Circuit of Figure 11) (Continued)
TA=25
oC
V+=2V
+2
+1
0
-1
-2
SLOPE 150Ω
012345678
LOAD CURRENT IL(mA)
OUTPUT VOLTAGE
100
90
80
70
60
50
40
30
20
10
0
POWER CONVERSION EFFICIENCY (%)
PEFF
I+
LOAD CURRENT IL(mA)
0 1.5 3.0 4.5 6.0 7.5 9.0
20.0
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0
SUPPLY CURRENT (mA) (NOTE 6)
TA=25
oC
V+=2V
1
2
3
4
8
7
6
5
+
-
C1
10µF
ISV+(+5V)
IL
RL
-VOUT
C2
10µF
ICL7660
COSC
+
-
(NOTE)
ICL7660A
ICL7660, ICL7660A
6
The voltage regulator portion of the ICL7660 and ICL7660A is
an integral partof the anti-latchup circuitry, however its inherent
voltage drop can degrade operation at low voltages. Therefore,
to improve low voltage operation the “LV” pin should be
connected to GROUND, disabling the regulator. For supply
voltages greater than 3.5V the LV terminal must be left open to
insure latchup proof operation, and prevent device damage.
Theoretical Power Efficiency
Considerations
In theory a voltage converter can approach 100% efficiency
if certain conditions are met.
1. The driver circuitry consumes minimal power.
2. The output switches have extremely low ON resistance
and virtually no offset.
3. Theimpedancesofthepumpandreservoircapacitorsare
negligible at the pump frequency.
The ICL7660 and ICL7660A approach these conditions for
negative voltage conversion if large values of C1and C2
are used.
ENERGY IS LOST ONLY IN THE TRANSFER OF
CHARGE BETWEEN CAPACITORS IF A CHANGE IN
VOLTAGE OCCURS. The energy lost is defined by:
E=1/2C1(V12-V
22)
where V1and V2are the voltages on C1during the pump and
transfer cycles. If the impedances of C1and C2are relatively
high at the pump frequency (refer to Figure 12) compared to
the value of RL, there will be a substantial difference in the
voltages V1and V2. Therefore it is not onlydesirable to make
C2as large as possible to eliminate output voltage ripple, but
also to employ a correspondingly large value for C1in order to
achieve maximum efficiency of operation.
Do’s And Don’ts
1. Do not exceed maximum supply voltages.
2. Do not connect LV terminal to GROUND for supply
voltages greater than 3.5V.
3. Do not short circuit the output to V+ supply for supply
voltages above 5.5V for extended periods, however,
transient conditions including start-up are okay.
4. When using polarized capacitors, the + terminalof C1
must be connected to pin 2 of the ICL7660 and ICL7660A
and the + terminal of C2must be connected to GROUND.
5. If the voltage supply driving the ICL7660 and ICL7660A
has a large source impedance (25Ω-30Ω), then a 2.2µF
capacitor from pin 8 to ground may be required to limit
rate of rise of input voltage to less than 2V/µs.
6. User should insure that the output (pin 5) does not go
more positive than GND (pin3). Devicelatchupwill occur
under these conditions. A 1N914 or similar diode placed
in parallel with C2will prevent the device from latching up
under these conditions. (Anode pin 5, Cathode pin 3).
VOUT =-V
IN
C2
VIN
C1
S3S4
S1S2
8
3
2
5
3
7
FIGURE 12. IDEALIZED NEGATIVE VOLTAGE CONVERTER
FIGURE 13A. CONFIGURATION FIGURE 13B. THEVENIN EQUIVALENT
FIGURE 13. SIMPLE NEGATIVE CONVERTER
1
2
3
4
8
7
6
5
+
-
10µF
ICL7660
VOUT =-V+
V+
+
-
10µF
ICL7660A V++
-
ROVOUT
ICL7660, ICL7660A
7
Typical Applications
Simple Negative Voltage Converter
The majority of applications will undoubtedly utilize the ICL7660
and ICL7660A for generation of negative supply voltages.
Figure 13 shows typical connections to provide a negative
supply negative (GND) for supply voltages below 3.5V.
The output characteristics of the circuit in Figure 13A can be
approximated by an ideal voltage source in series with a
resistance as shown in Figure 13B. The voltage source has
a value of -V+. The output impedance (RO) is a function of
the ON resistance of the internal MOS switches (shown in
Figure 12), the switching frequency, the value of C1and C2,
and the ESR (equivalent series resistance) of C1 and C2. A
good first order approximation for ROis:
RSW, the total switch resistance, is a function of supply
voltage and temperature (See theOutput Source Resistance
graphs), typically 23Ωat 25oC and 5V. Careful selection of
C1and C2will reduce the remaining terms, minimizing the
output impedance. High value capacitors will reduce the
1/(fPUMP •C1) component, and low ESR capacitors will
lower the ESR term. Increasing the oscillator frequency will
reduce the 1/(fPUMP • C1) term, but may have the side effect
of a net increase in output impedance when C1>10µFand
there is no longer enough time to fully charge the capacitors
FIGURE 14. OUTPUT RIPPLE
FIGURE 15. PARALLELING DEVICES
FIGURE 16. CASCADING DEVICES FOR INCREASED OUTPUT VOLTAGE
A
t
2
t
1
B
0
-(V+)
V
1
2
3
4
8
7
6
5
ICL7660
V+
C1ICL7660A 1
2
3
4
8
7
6
5
ICL7660
C1ICL7660A
RL
+
-
C2
“n”
“1”
1
2
3
4
8
7
6
5
V+
1
2
3
4
8
7
6
5
+
-
10µF
+
-
10µF
+
-
10µF+
-
10µF
VOUT =-nV+
ICL7660
ICL7660A
“n”
ICL7660
ICL7660A
“1”
RO≅2(RSW1 +R
SW3 + ESRC1)+
2(RSW2 +R
SW4 + ESRC1)+
1+ ESRC2
(fPUMP)(C1)
(fPUMP =fOSC ,R
SWX = MOSFET switch resistance)
2
Combining the four RSWX termsasR
SW, we see that:
RO≅2(R
SW)+ 1+4(ESR
C1) + ESRC2
(fPUMP)(C1)
RO≅2(RSW1 +R
SW3 + ESRC1)+
ICL7660, ICL7660A
8
everycycle.In a typical application where fOSC = 10kHz and
C=C
1=C
2=10µF:
RO≅46+20+5(ESR
C)
Since the ESRs of the capacitors are reflected in the output
impedance multiplied by a factor of 5, a high value could
potentially swamp out a low 1/(fPUMP •C1) term, rendering an
increase in switching frequency or filter capacitance ineffective.
Typical electrolytic capacitors may have ESRs as high as 10Ω.
RO/ ≅46 + 20 + 5 (ESRC)
Since the ESRs of the capacitors are reflected in the output
impedance multiplied by a factor of 5, a high value could
potentially swamp out a low 1/(fPUMP •C1) term, rendering an
increase in switching frequency or filter capacitance ineffective.
Typical electrolytic capacitors may have ESRs as high as 10Ω.
Output Ripple
ESR also affects the ripple voltage seen at the output. The
total ripple is determined by 2 voltages, A and B, as shown in
Figure 14. Segment A is the voltage drop across the ESR of
C2at the instant it goes from being charged by C1(current
flow into C2) to being discharged through the load (current
flowing out of C2). The magnitude of this current change is
2•IOUT, hence the total drop is 2•IOUT •eSRC2V. Segment
B is the voltage change across C2during time t2, the half of
thecyclewhenC
2supplies current to the load. The drop at B
is lOUT • t2/C2V. The peak-to-peak ripple voltage is the sum
of these voltage drops:
Again, a low ESR capacitor will reset in a higher
performance output.
Paralleling Devices
Any number of ICL7660 and ICL7660A voltage converters
may be paralleled to reduce output resistance. The reservoir
capacitor, C2, serves all devices while each device requires
its own pump capacitor, C1. The resultant output resistance
would be approximately:
Cascading Devices
The ICL7660 and ICL7660A may be cascaded as shown to
produced larger negative multiplication of the initial supply
voltage. However, due to the finite efficiency of each device,
the practical limit is 10 devices for light loads. The output
voltage is defined by:
VOUT =-n(V
IN),
where n is an integer representing the number of devices
cascaded. The resulting output resistance would be
approximately the weighted sum of the individual ICL7660
and ICL7660A ROUT values.
Changing the ICL7660/ICL7660A Oscillator
Frequency
It may be desirable in some applications, due to noise or
other considerations, to increase the oscillator frequency.
This is achieved by overdriving the oscillator from an
external clock, as shown in Figure 17. In order to prevent
possible device latchup, a 1kΩresistor must be used in
series with the clock output. In a situation where the
designer has generated the external clock frequency using
TTL logic, the addition of a 10kΩpullup resistor to V+ supply
is required. Note that the pump frequency with external
clocking, as with internal clocking, will be 1/2of the clock
frequency. Output transitions occur on the positive-going
edge of the clock.
It is also possible to increase the conversion efficiency of the
ICL7660 and ICL7660A at low load levels by lowering the
oscillator frequency. This reduces the switching losses, and is
shown in Figure 18. However, lowering the oscillator
frequency will cause an undesirable increase in the
impedance of the pump (C1) and reservoir (C2) capacitors;
this is overcome byincreasing the values ofC1and C2by the
same factor that the frequency has been reduced. For
example, the addition of a 100pF capacitor between pin 7
(OSC) and V+ will lower the oscillator frequency to 1kHz from
its nominal frequency of 10kHz (a multiple of 10), and thereby
necessitate a corresponding increase in the value of C1and
C2(from 10µF to 100µF).
RO≅2(23)+ 1+4(ESR
C1)+ESR
C2
(5 •103)(10
-5)
RO≅2(23)+ 1+4(ESR
C1)+ESR
C2
(5 •103)(10-
5)
VRIPPLE
≅[1+ 2 (ESRC2)]
IOUT
2(f
PUMP)(C2)
ROUT =ROUT (of ICL7660/ICL7660A)
n (number of devices)
1
2
3
4
8
7
6
5
+
-
10µFICL7660
VOUT
V+
+
-10µF
V+
CMOS
GATE
1kΩ
ICL7660A
FIGURE 17. EXTERNAL CLOCKING
ICL7660, ICL7660A
9
Positive Voltage Doubling
The ICL7660 and ICL7660A may be employed to achieve
positive voltage doubling using the circuit shown in Figure
19. In this application, the pump inverter switches of the
ICL7660 and ICL7660Aare used to charge C1toavoltage
level of V+ -VF(where V+ is the supply voltage and VFis the
forward voltage drop of diode D1). On the transfer cycle, the
voltage on C1plus the supply voltage (V+) is applied through
diode D2to capacitor C2. The voltage thus created on C2
becomes (2V+) - (2VF) or twice the supply voltage minus the
combined forward voltage drops of diodes D1and D2.
The source impedance of the output (VOUT) will depend on
the output current, but for V+ = 5V and an output current of
10mA it will be approximately 60Ω.
Combined Negative Voltage Conversion
and Positive Supply Doubling
Figure 20 combines the functions shown in Figures 13 and
Figure 19 to provide negative voltage conversion and
positive voltage doubling simultaneously. This approach
would be, for example, suitable for generating +9V and -5V
from an existing +5V supply. In this instance capacitors C1
and C3perform the pump and reservoir functions
respectively for the generation of the negative voltage, while
capacitors C2and C4are pump and reservoir respectively
for the doubled positive voltage. There is a penalty in this
configuration which combines both functions, however, in
that the source impedances of the generated supplies will be
somewhat higher due to thefinite impedance ofthe common
charge pump driver at pin 2 of the device.
Voltage Splitting
The bidirectional characteristics can also be used to split a
higher supply in half, as shown in Figure 21. The combined
load will be evenly shared between the two sides. Because
the switches share the loadin parallel, the output impedance
is much lower than in the standard circuits, and higher
currents can be drawn from the device. By using this circuit,
and then the circuit of Figure 16, +15V can be converted (via
+7.5, and -7.5) to a nominal -15V, although with rather high
series output resistance (~250Ω).
Regulated Negative Voltage Supply
In some cases, the output impedance of the ICL7660 and
ICL7660A can be a problem, particularly if the load current
varies substantially. The circuit of Figure 22 can be used to
overcome this by controlling the input voltage, via an ICL7611
low-power CMOS op amp, in such a way as to maintain a
nearly constant output voltage. Direct feedback is inadvisable,
since the ICL7660s and ICL7660As output does not respond
instantaneously to change in input, but only after the switching
delay. The circuit shown supplies enough delay to
accommodate the ICL7660 and ICL7660A, while maintaining
adequate feedback. An increase in pump and storage
capacitors is desirable, and the values shown provides an
output impedance of less than 5Ωto a load of 10mA.
1
2
3
4
8
7
6
5
+
-VOUT
V+
+
-C2
C1
COSC
ICL7660
ICL7660A
FIGURE 18. LOWERING OSCILLATOR FREQUENCY
1
2
3
4
8
7
6
5
V+
D2
C1C2
VOUT =
(2V+) - (2VF)
+
-
+
-
D1
ICL7660
ICL7660A
FIGURE 19. POSITIVE VOLT DOUBLER
1
2
3
4
8
7
6
5
V+
D1
D2
C4
VOUT =(2V+)-
(VFD1)-(VFD2)
+
-
C2
+
-
C3
+
-
VOUT =
-(nVIN -V
FDX)
C1
+
-
ICL7660
ICL7660A
FIGURE 20. COMBINED NEGATIVE VOLTAGE CONVERTER
AND POSITIVE DOUBLER
1
2
3
4
8
7
6
5
+
-
+
-
50µF
50µF
+
-
50µF
RL1
VOUT =V+ - V-
2
V+
V-
RL2
ICL7660
ICL7660A
FIGURE 21. SPLITTING A SUPPLY IN HALF
ICL7660, ICL7660A
10
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Intersil Corporation’s quality certifications can be viewed at website www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice.
Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. How-
ever, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No
license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
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Other Applications
Further information on the operation and use of the ICL7660
and ICL7660A may be found in AN051 “Principals and
Applications of the ICL7660 and ICL7660A CMOS Voltage
Converter”.
1
2
3
4
8
7
6
5
+
-
100µF
100µF
VOUT
+
-10µF
ICL7611
+
-100Ω
50K
+8V
100K
50K
ICL8069
56K
+8V
800K 250K
VOLTAGE
ADJUST
-
+
ICL7660
ICL7660A
FIGURE 22. REGULATING THE OUTPUT VOLTAGE
1
2
3
4
8
7
6
5
+
-
+
-
10µF
16
TTL DATA
INPUT
15
4
10µF
13 14
12 11
+5V LOGIC SUPPLY
RS232
DATA
OUTPUT
IH5142
1
3+5V
-5V
ICL7660
ICL7660A
FIGURE 23. RS232 LEVELS FROM A SINGLE 5V SUPPLY
ICL7660, ICL7660A
