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 input range 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 (V
OUT
= (-) nV
IN
)
Typical Open Circuit Voltage Conversion Efficiency 99.9%
Typical Power Efficiency 98%
Wide Operating Voltage Range
- ICL7660 . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5V to 10.0V
- ICL7660A . . . . . . . . . . . . . . . . . . . . . . . . . 1.5V to 12.0V
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
Processor (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 (
o
C)
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
0 to 70
8 Pin Metal Can
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
V
OUT
V+ (AND CASE)
LV
CAP+
NC
GND
OSC
V
OUT
2
4
6
1
3
7
5
8
CAP-
Data Sheet
April 1999
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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
(Note 2) . . . . . . . . . . . . . . (V+ -5.5V) to (V+ +0.3V) for V+ > 5.5V
Current into LV (Note 2) . . . . . . . . . . . . . . . . . . . 20
A for V+ > 3.5V
Output Short Duration (V
SUPPLY
5.5V) . . . . . . . . . . . .Continuous
Operating Conditions
Temperature Range
ICL7660M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55
o
C to 125
o
C
ICL7660C, ICL7660AC. . . . . . . . . . . . . . . . . . . . . . . . 0
o
C to 70
o
C
ICL7660AI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40
o
C to 85
o
C
Thermal Resistance (Typical, Note 1)
JA
(
o
C/W)
JC
(
o
C/W)
PDIP Package . . . . . . . . . . . . . . . . . . .
150
N/A
SOIC Package . . . . . . . . . . . . . . . . . . .
165
N/A
Metal Can Package (ICL7660 Only) . .
160
70
Maximum Storage Temperature Range . . . . . . . . . . -65
o
C to 150
o
C
Maximum Lead Temperature (Soldering, 10s). . . . . . . . . . . . . 300
o
C
(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 operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE:
1.
JA
is measured with the component mounted on an evaluation PC board in free air.
Electrical Specifications
ICL7660 and ICL7660A, V+ = 5V, T
A
= 25
o
C, C
OSC
= 0, Test Circuit Figure 11
Unless Otherwise Specified
PARAMETER
SYMBOL
TEST CONDITIONS
ICL7660
ICL7660A
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
Supply Current
I+
R
L
=
-
170
500
-
80
165
A
Supply Voltage Range - Lo
V
L
+
MIN
T
A
MAX, R
L
= 10k
, LV to GND
1.5
-
3.5
1.5
-
3.5
V
Supply Voltage Range - Hi
V
H
+
MIN
T
A
MAX, R
L
= 10k
, LV to Open
3.0
-
10.0
3
-
12
V
Output Source Resistance
R
OUT
I
OUT
= 20mA, T
A
= 25
o
C
-
55
100
-
60
100
I
OUT
= 20mA, 0
o
C
T
A
70
o
C
-
-
120
-
-
120
I
OUT
= 20mA, -55
o
C
T
A
125
o
C
-
-
150
-
-
-
I
OUT
= 20mA, -40
o
C
T
A
85
o
C
-
-
-
-
-
120
V
+
= 2V, I
OUT
= 3mA, LV to GND
0
o
C
T
A
70
o
C
-
-
300
-
-
300
V+ = 2V, I
OUT
= 3mA, LV to GND,
-55
o
C
T
A
125
o
C
-
-
400
-
-
-
Oscillator Frequency
f
OSC
-
10
-
-
10
-
kHz
Power Efficiency
P
EF
R
L
= 5k
95
98
-
96
98
-
%
Voltage Conversion Efficiency
V
OUT EF
R
L
=
97
99.9
-
99
99.9
-
%
Oscillator Impedance
Z
OSC
V+ = 2V
-
1.0
-
-
1
-
M
V = 5V
-
100
-
-
-
-
k
ICL7660A, V+ = 3V, T
A
= 25
o
C, OSC = Free running, Test Circuit Figure 11, Unless Otherwise Specified
Supply Current (Note 3)
I+
V+ = 3V, R
L
=
, 25
o
C
-
-
-
-
26
100
A
0
o
C < T
A
< 70
o
C
-
-
-
-
-
125
A
-40
o
C < T
A
< 85
o
C
-
-
-
-
-
125
A
Output Source Resistance
R
OUT
V+ = 3V, I
OUT
= 10mA
-
-
-
-
97
150
0
o
C < T
A
< 70
o
C
-
-
-
-
-
200
-40
o
C < T
A
< 85
o
C
-
-
-
-
-
200
Oscillator Frequency (Note 3)
f
OSC
V+ = 3V (same as 5V conditions)
-
-
-
5.0
8
-
kHz
0
o
C < T
A
< 70
o
C
-
-
-
3.0
-
-
kHz
-40
o
C < T
A
< 85
o
C
-
-
-
3.0
-
-
kHz
ICL7660, ICL7660A
3
Functional Block Diagram
Voltage Conversion Efficiency
V
OUT
EFF V+ = 3V, R
L
=
-
-
-
99
-
-
%
T
MIN
< T
A
< T
MAX
-
-
-
99
-
-
%
Power Efficiency
P
EFF
V+ = 3V, R
L
= 5k
-
-
-
96
-
-
%
T
MIN
< 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 50
o
C by 5.5mW/
o
C.
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 usually a 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, T
A
= 25
o
C, C
OSC
= 0, Test Circuit Figure 11
Unless Otherwise Specified (Continued)
PARAMETER
SYMBOL
TEST CONDITIONS
ICL7660
ICL7660A
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
RC
OSCILLATOR
2
VOLTAGE
LEVEL
TRANSLATOR
VOLTAGE
REGULATOR
LOGIC
NETWORK
OSC
LV
V+
CAP+
CAP-
V
OUT
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 (
o
C)
SU
P
P
L
Y
VO
L
T
A
G
E
(
V
)
10K
T
A
= 25
o
C
1000
100
10
0
1
2
3
4
5
6
7
8
SUPPLY VOLTAGE (V+)
O
U
T
P
UT
S
O
URCE
RE
S
I
S
T
ANCE
(
)
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 A FUNCTION OF OUTPUT
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 (
o
C)
O
U
T
P
U
T
S
O
UR
CE
RE
S
I
S
T
ANCE
(
)
I
OUT
= 1mA
V+ = +2V
V+ = 5V
PO
WE
R
C
O
N
VE
R
S
I
O
N
E
F
F
I
C
I
EN
C
Y
(
%
)
T
A
= 25
o
C
I
OUT
= 1mA
I
OUT
= 15mA
100
98
96
94
92
90
88
86
84
82
80
100
1K
10K
OSC. FREQUENCY f
OSC
(Hz)
V+ = +5V
O
S
CIL
L
A
T
O
R
F
RE
Q
U
E
NCY
f
OSC
(H
z
)
10K
1K
100
10
V+ = 5V
T
A
= 25
o
C
1.0
10
100
1000
10K
C
OSC
(pF)
20
18
16
14
12
10
8
6
-50
-25
0
25
50
75
100
125
O
S
CIL
L
A
T
O
R
F
R
E
Q
UE
NCY
f
OS
C
(k
H
z
)
TEMPERATURE (
o
C)
V+ = +5V
T
A
= 25
o
C
V+ = +5V
5
4
3
2
1
0
-1
-2
-3
-4
-5
O
U
T
P
U
T
V
O
LTA
G
E
LOAD CURRENT I
L
(mA)
SLOPE 55
0
10
20
30
40
50
60
70
80
P
EFF
I
+
T
A
= 25
o
C
V
+
= +5V
S
U
P
P
L
Y
CURRE
NT
I+
(
m
A)
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
P
O
W
E
R
C
O
N
V
E
RS
IO
N
E
F
F
ICIE
NCY
(
%
)
LOAD CURRENT I
L
(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
10
F 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 C
1
is charged to a voltage, V+, for the half cycle
when switches S
1
and S
3
are closed. (Note: Switches S
2
and S
4
are open during this half cycle.) During the second
half cycle of operation, switches S
2
and S
4
are closed, with
S
1
and S
3
open, thereby shifting capacitor C
1
negatively by
V+ volts. Charge is then transferred from C
1
to C
2
such that
the voltage on C
2
is exactly V+, assuming ideal switches and
no load on C
2
. 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; S
1
is a P-Channel device and S
2
,
S
3
and S
4
are N-Channel devices. The main difficulty with
this approach is that in integrating the switches, the
substrates of S
3
and S
4
must 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 (V
OUT
= 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 (V
OUT
) together
with the level translators, and switches the substrates of S
3
and
S
4
to the correct level to maintain necessary reverse bias.
FIGURE 9. OUTPUT VOLTAGE AS A FUNCTION OF OUTPUT
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 R
L
from 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, V
OUT
2V
IN
, I
S
2I
L
, so V
IN
x I
S
V
OUT
x I
L
.
NOTE: For large values of C
OSC
(>1000pF) the values of C
1
and C2 should be increased to 100
F.
FIGURE 11. ICL7660, ICL7660A TEST CIRCUIT
Typical Performance Curves
(Test Circuit of Figure 11) (Continued)
T
A
= 25
o
C
V+ = 2V
+2
+1
0
-1
-2
SLOPE 150
0
1
2
3
4
5
6
7
8
LOAD CURRENT I
L
(mA)
O
U
T
P
UT
V
O
L
T
AG
E
100
90
80
70
60
50
40
30
20
10
0
P
O
W
E
R
C
O
N
V
E
RS
IO
N
E
F
F
I
CIE
NCY
(
%
)
P
EFF
I+
LOAD CURRENT I
L
(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
S
U
P
P
L
Y
CURRE
NT
(
m
A)
(
N
O
T
E
6
)
T
A
= 25
o
C
V+ = 2V
1
2
3
4
8
7
6
5
+
-
C
1
10
F
I
S
V+
(+5V)
I
L
R
L
-V
OUT
C
2
10
F
ICL7660
C
OSC
+
-
(NOTE)
ICL7660A
ICL7660, ICL7660A
6
The voltage regulator portion of the ICL7660 and ICL7660A is
an integral part of 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. The impedances of the pump and reservoir capacitors are
negligible at the pump frequency.
The ICL7660 and ICL7660A approach these conditions for
negative voltage conversion if large values of C
1
and C
2
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
/
2
C
1
(V
1
2
- V
2
2
)
where V
1
and V
2
are the voltages on C
1
during the pump and
transfer cycles. If the impedances of C
1
and C
2
are relatively
high at the pump frequency (refer to Figure 12) compared to
the value of R
L
, there will be a substantial difference in the
voltages V
1
and V
2
. Therefore it is not only desirable to make
C
2
as large as possible to eliminate output voltage ripple, but
also to employ a correspondingly large value for C
1
in 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 + terminal of C
1
must be connected to pin 2 of the ICL7660 and ICL7660A
and the + terminal of C
2
must be connected to GROUND.
5. If the voltage supply driving the ICL7660 and ICL7660A
has a large source impedance (25
- 30
), then a 2.2
F
capacitor from pin 8 to ground may be required to limit
rate of rise of input voltage to less than 2V/
s.
6. User should insure that the output (pin 5) does not go
more positive than GND (pin 3). Device latch up will occur
under these conditions. A 1N914 or similar diode placed
in parallel with C
2
will prevent the device from latching up
under these conditions. (Anode pin 5, Cathode pin 3).
V
OUT
= -V
IN
C
2
V
IN
C
1
S
3
S
4
S
1
S
2
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
+
-
10
F
ICL7660
V
OUT
=
-
V+
V+
+
-
10
F
ICL7660A
V+
+
-
R
O
V
OUT
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 (R
O
) is a function of
the ON resistance of the internal MOS switches (shown in
Figure 12), the switching frequency, the value of C
1
and C
2
,
and the ESR (equivalent series resistance) of C1 and C2. A
good first order approximation for R
O
is:
RSW, the total switch resistance, is a function of supply
voltage and temperature (See the Output Source Resistance
graphs), typically 23
at 25
o
C and 5V. Careful selection of
C
1
and C
2
will reduce the remaining terms, minimizing the
output impedance. High value capacitors will reduce the
1/(f
PUMP
C
1
) component, and low ESR capacitors will
lower the ESR term. Increasing the oscillator frequency will
reduce the 1/(f
PUMP
C1) term, but may have the side effect
of a net increase in output impedance when C
1
> 10
F and
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+
C
1
ICL7660A
1
2
3
4
8
7
6
5
ICL7660
C
1
ICL7660A
R
L
+
-
C
2
"n"
"1"
1
2
3
4
8
7
6
5
V+
1
2
3
4
8
7
6
5
+
-
10
F
+
-
10
F
+
-
10
F
+
-
10
F
V
OUT
=
-
nV+
ICL7660
ICL7660A
"n"
ICL7660
ICL7660A
"1"
R
O
2(R
SW1
+ R
SW3
+ ESR
C1
) +
2(R
SW2
+ R
SW4
+ ESR
C1
) +
1
+ ESR
C2
(f
PUMP
) (C1)
(f
PUMP
=
f
OSC
, R
SWX
= MOSFET switch resistance)
2
Combining the four R
SWX
terms as R
SW
, we see that:
R
O
2 (R
SW
) +
1
+ 4 (ESR
C1
) + ESR
C2
(f
PUMP
) (C1)
R
O
2(R
SW1
+ R
SW3
+ ESR
C1
) +
ICL7660, ICL7660A
8
every cycle. In a typical application where f
OSC
= 10kHz and
C = C
1
= C
2
= 10
F:
R
O
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/(f
PUMP
C
1
) term, rendering an
increase in switching frequency or filter capacitance ineffective.
Typical electrolytic capacitors may have ESRs as high as 10
.
R
O/
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/(f
PUMP
C
1
) term, rendering an
increase in switching frequency or filter capacitance ineffective.
Typical electrolytic capacitors may have ESRs as high as 10
.
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
C
2
at the instant it goes from being charged by C
1
(current
flow into C
2
) to being discharged through the load (current
flowing out of C
2
). The magnitude of this current change is
2
I
OUT
, hence the total drop is 2
I
OUT
eSR
C2
V. Segment
B is the voltage change across C
2
during time t
2
, the half of
the cycle when C
2
supplies current to the load. The drop at B
is l
OUT
t2/C
2
V. 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, C
2
, serves all devices while each device requires
its own pump capacitor, C
1
. 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:
V
OUT
= -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 R
OUT
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 1k
resistor 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 10k
pullup resistor to V+ supply
is required. Note that the pump frequency with external
clocking, as with internal clocking, will be
1
/
2
of 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 (C
1
) and reservoir (C
2
) capacitors;
this is overcome by increasing the values of C
1
and C
2
by 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 C
1
and
C
2
(from 10
F to 100
F).
R
O
2 (23) +
1
+ 4 (ESR
C1
) + ESR
C2
(5
10
3
) (10
-5
)
R
O
2 (23) +
1
+ 4 (ESR
C1
) + ESR
C2
(5
10
3
) (10-
5
)
V
RIPPLE
[
1
+ 2 (ESR
C2
)
]
I
OUT
2 (f
PUMP
) (C2)
R
OUT
=
R
OUT
(of ICL7660/ICL7660A)
n (number of devices)
1
2
3
4
8
7
6
5
+
-
10
F
ICL7660
V
OUT
V+
+
-
10
F
V+
CMOS
GATE
1k
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 ICL7660A are used to charge C
1
to a voltage
level of V+ -V
F
(where V+ is the supply voltage and V
F
is the
forward voltage drop of diode D
1
). On the transfer cycle, the
voltage on C
1
plus the supply voltage (V+) is applied through
diode D
2
to capacitor C
2
. The voltage thus created on C
2
becomes (2V+) - (2VF) or twice the supply voltage minus the
combined forward voltage drops of diodes D
1
and D
2
.
The source impedance of the output (V
OUT
) will depend on
the output current, but for V+ = 5V and an output current of
10mA it will be approximately 60
.
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 C
1
and C
3
perform the pump and reservoir functions
respectively for the generation of the negative voltage, while
capacitors C
2
and C
4
are 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 the finite impedance of the 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 load in 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 (
~
250
).
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 5
to a load of 10mA.
1
2
3
4
8
7
6
5
+
-
V
OUT
V+
+
-
C
2
C
1
C
OSC
ICL7660
ICL7660A
FIGURE 18. LOWERING OSCILLATOR FREQUENCY
1
2
3
4
8
7
6
5
V+
D
2
C
1
C
2
V
OUT
=
(2V+) - (2V
F
)
+
-
+
-
D
1
ICL7660
ICL7660A
FIGURE 19. POSITIVE VOLT DOUBLER
1
2
3
4
8
7
6
5
V+
D
1
D
2
C
4
V
OUT
= (2V+)
-
(V
FD1
)
-
(V
FD2
)
+
-
C
2
+
-
C
3
+
-
V
OUT
=
-
(nV
IN
- V
FDX
)
C
1
+
-
ICL7660
ICL7660A
FIGURE 20. COMBINED NEGATIVE VOLTAGE CONVERTER
AND POSITIVE DOUBLER
1
2
3
4
8
7
6
5
+
-
+
-
50
F
50
F
+
-
50
F
R
L1
V
OUT
= V+ - V-
2
V+
V
-
R
L2
ICL7660
ICL7660A
FIGURE 21. SPLITTING A SUPPLY IN HALF
ICL7660, ICL7660A
10
All Intersil products are manufactured, assembled and tested utilizing ISO9000 quality systems.
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.
For information regarding Intersil Corporation and its products, see web site www.intersil.com
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
+
-
100
F
100
F
V
OUT
+
-
10
F
ICL7611
+
-
100
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
+
-
+
-
10
F
16
TTL DATA
INPUT
15
4
10
F
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
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