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ICL7660, ICL7660A
Data Sheet April 1999 File Number
3072.4
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 NChannel 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 = (-) nVIN) · 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 µProcessor (8080 Type) Negative Supplies · Inexpensive Negative Supplies · Data Acquisition Systems
Pinouts
ICL7660, ICL7660A (PDIP, SOIC) TOP VIEW
NC CAP+ GND CAP-
1 2 3 4
8 7 6 5
V+ OSC LV VOUT
Ordering Information
PART NO. ICL7660CBA ICL7660CBA-T ICL7660CPA ICL7660MTV ICL7660ACBA ICL7660ACBA-T ICL7660ACPA ICL7660AIBA ICL7660AIBA-T ICL7660AIPA TEMP. RANGE (oC) 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 -40 to 85 -40 to 85 -40 to 85 PACKAGE 8 Ld SOIC (N) 8 Ld SOIC (N) Tape and Reel 8 Ld PDIP 8 Pin Metal Can 8 Ld SOIC (N) 8 Ld SOIC (N) Tape and Reel 8 Ld PDIP 8 Ld SOIC (N) 8 Ld SOIC (N) Tape and Reel 8 Ld PDIP PKG. NO. M8.15 M8.15 E8.3 T8.C M8.15 M8.15
ICL7660 (METAL CAN) TOP VIEW
V+ (AND CASE) 8 NC 1 7 OSC
CAP+
2
6
LV
GND
3 4 CAP-
5
VOUT
E8.3 M8.15 M8.15 E8.3
Add /883B to part number if 883B processing is required.
3-26
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. http://www.intersil.com or 407-727-9207 | Copyright © Intersil Corporation 1999
ICL7660, ICL7660A
C
Absolute Maximum Ratings
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) . . . . . . . . . . . . . . . . . . . 20µA for V+ > 3.5V Output Short Duration (VSUPPLY 5.5V) . . . . . . . . . . . .Continuous
Thermal Information
Thermal Resistance (Typical, Note 1) JA (oC/W) JC (oC/W) PDIP Package . . . . . . . . . . . . . . . . . . . 150 N/A SOIC Package . . . . . . . . . . . . . . . . . . . 165 N/A Metal Can Package (ICL7660 Only). . . 160 70 Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC Maximum Lead Temperature (Soldering, 10s). . . . . . . . . . . . .300oC (SOIC - Lead Tips Only)
Operating Conditions
Temperature Range ICL7660M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55oC to 125oC ICL7660C, ICL7660AC. . . . . . . . . . . . . . . . . . . . . . . . 0oC to 70oC ICL7660AI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40oC to 85oC
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, TA = 25oC, COSC = 0, Test Circuit Figure 11 Unless Otherwise Specified ICL7660 ICL7660A MAX 500 3.5 10.0 100 120 150 300 400 MIN 1.5 3 96 99 TYP 80 60 10 98 99.9 1 MAX UNITS 165 3.5 12 100 120 120 300 µA V V kHz % % M k
PARAMETER Supply Current Supply Voltage Range - Lo Supply Voltage Range - Hi Output Source Resistance
SYMBOL I+ VL+ VH+ ROUT RL =
TEST CONDITIONS
MIN 1.5 3.0 -
TYP 170 55 10 98 99.9 1.0 100
MIN TA MAX, RL = 10k, LV to GND MIN TA MAX, RL = 10k, LV to Open IOUT = 20mA, IOUT = 20mA, IOUT = 20mA, IOUT = 20mA, TA = 25oC 0oC TA 70oC -55oC TA 125oC -40oC TA 85oC
V+ = 2V, IOUT = 3mA, LV to GND 0oC TA 70oC V+ = 2V, IOUT = 3mA, LV to GND, -55oC TA 125oC Oscillator Frequency Power Efficiency Voltage Conversion Efficiency Oscillator Impedance fOSC PEF VOUT EF ZOSC RL = 5k RL = V+ = 2V V = 5V
95 97 -
ICL7660A, V+ = 3V, TA = 25oC, OSC = Free running, Test Circuit Figure 11, Unless Otherwise Specified Supply Current (Note 3) I+ V+ = 3V, RL = , 25oC oC < T < 70oC 0 A -40oC < TA < 85oC Output Source Resistance ROUT V+ = 3V, IOUT = 10mA 0oC < TA < 70oC -40oC < TA < 85oC Oscillator Frequency (Note 3) fOSC V+ = 3V (same as 5V conditions) 0oC < TA < 70oC -40oC < TA < 85oC -
5.0 3.0 3.0
26 97 8 -
100 125 125 150 200 200 -
µA µA µA kHz kHz kHz
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ICL7660, ICL7660A
Electrical Specifications
ICL7660 and ICL7660A, V+ = 5V, TA = 25oC, COSC = 0, Test Circuit Figure 11 Unless Otherwise Specified (Continued) ICL7660 PARAMETER Voltage Conversion Efficiency SYMBOL TEST CONDITIONS MIN TYP MAX VOUTEFF V+ = 3V, RL = TMIN < TA < TMAX Power Efficiency PEFF V+ = 3V, RL = 5k TMIN < TA < TMAX 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 50oC by 5.5mW/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 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. ICL7660A MIN 99 99 96 95 TYP MAX UNITS % % % %
Functional Block Diagram
V+ CAP+ RC OSCILLATOR
÷2
VOLTAGE LEVEL TRANSLATOR
CAP-
VOUT OSC LV
VOLTAGE REGULATOR
LOGIC NETWORK
Typical Performance Curves
10
(Test Circuit of Figure 11)
10K OUTPUT SOURCE RESISTANCE () TA = 25oC
8 SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE RANGE (NO DIODE REQUIRED)
1000
6
4
100
2
0 -55
10 -25 0 25 50 100 125 0 1 2 3 4 5 6 7 8 TEMPERATURE (oC) SUPPLY VOLTAGE (V+)
FIGURE 1. OPERATING VOLTAGE AS A FUNCTION OF TEMPERATURE
FIGURE 2. OUTPUT SOURCE RESISTANCE AS A FUNCTION OF SUPPLY VOLTAGE
3-28
ICL7660, ICL7660A Typical Performance Curves
350 OUTPUT SOURCE RESISTANCE () IOUT = 1mA 300 250 200 150 100 50 0 -55 V+ = +2V POWER CONVERSION EFFICIENCY (%)
(Test Circuit of Figure 11) (Continued)
100 98 96 94 92 90 88 86 84 82
TA = 25oC IOUT = 1mA
IOUT = 15mA
V+ = 5V -25 0 25 50 75 100 125
V+ = +5V 80 100
1K OSC. FREQUENCY fOSC (Hz)
10K
TEMPERATURE (oC)
FIGURE 3. OUTPUT SOURCE RESISTANCE AS A FUNCTION OF TEMPERATURE
FIGURE 4. POWER CONVERSION EFFICIENCY AS A FUNCTION OF OSC. FREQUENCY
10K OSCILLATOR FREQUENCY fOSC (kHz) OSCILLATOR FREQUENCY fOSC (Hz)
20 18 16 14 12 10 8 V+ = +5V 6 -50 -25 0 25 50 75 100 125
1K
100
10 1.0
V+ = 5V TA = 25oC 10 100 COSC (pF) 1000 10K
TEMPERATURE (oC)
FIGURE 5. FREQUENCY OF OSCILLATION AS A FUNCTION OF EXTERNAL OSC. CAPACITANCE
5 4 3 OUTPUT VOLTAGE 2 1 0 -1 -2 -3 -4 SLOPE 55 -5 0 10 20 30 40 50 LOAD CURRENT IL (mA) 60 70 80 TA = 25oC V+ = +5V
FIGURE 6. UNLOADED OSCILLATOR FREQUENCY AS A FUNCTION OF TEMPERATURE
100 POWER CONVERSION EFFICIENCY (%) 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 LOAD CURRENT IL (mA) 50 60 TA = 25oC V+ = +5V PEFF I+ 100 90 80 70 60 50 40 30 20 10 0 SUPPLY CURRENT I+ (mA)
FIGURE 7. OUTPUT VOLTAGE AS A FUNCTION OF OUTPUT CURRENT
FIGURE 8. SUPPLY CURRENT AND POWER CONVERSION EFFICIENCY AS A FUNCTION OF LOAD CURRENT
3-29
ICL7660, ICL7660A Typical Performance Curves
+2 TA = 25oC V+ = 2V +1 OUTPUT VOLTAGE
(Test Circuit of Figure 11) (Continued)
100 POWER CONVERSION EFFICIENCY (%) 90 80 70 60 50 40 30 20 10 0 0 1.5 3.0 4.5 6.0 7.5 9.0 LOAD CURRENT IL (mA) TA = 25oC V+ = 2V PEFF I+ 20.0 SUPPLY CURRENT (mA) (NOTE 6) 18.0 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0
0
-1 SLOPE 150 -2
0
1
2
3 4 5 LOAD CURRENT IL (mA)
6
7
8
FIGURE 9. OUTPUT VOLTAGE AS A FUNCTION OF OUTPUT CURRENT NOTE:
FIGURE 10. SUPPLY CURRENT AND POWER CONVERSION EFFICIENCY AS A FUNCTION OF LOAD CURRENT
6. These curves include in the supply current that current fed directly into the load RL 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, VOUT 2VIN, IS 2IL, so VIN x IS VOUT x IL.
IS V+ 1 2 C1 + 10µF ICL7660 ICL7660A 8 7 6 5 COSC (NOTE) RL IL (+5V)
-
3 4
-VOUT
C2 10µF +
NOTE: For large values of COSC (>1000pF) the values of C1 and C2 should be increased to 100µF. FIGURE 11. ICL7660, ICL7660A TEST CIRCUIT
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 C1 is charged to a voltage, V+, for the half cycle when switches S1 and S3 are closed. (Note: Switches S2 and S4 are open during this half cycle.) During the second half cycle of operation, switches S2 and S4 are closed, with S1 and S3 open, thereby shifting capacitor C1 negatively by V+ volts. Charge is then transferred from C1 to C2 such that the voltage on C2 is 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; S1 is a P-Channel device and S2 , S3 and S4 are N-Channel devices. The main difficulty with this approach is that in integrating the switches, the substrates of S3 and S4 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 (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 substrates of S3 and S4 to the correct level to maintain necessary reverse bias.
3-30
ICL7660, ICL7660A
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.
8 VIN 3 C1 3 S1 2 S2
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 C1 (V12 - V22) where V1 and V2 are the voltages on C1 during the pump and transfer cycles. If the impedances of C1 and C2 are 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 V1 and V2 . Therefore it is not only desirable to make C2 as large as possible to eliminate output voltage ripple, but also to employ a correspondingly large value for C1 in order to achieve maximum efficiency of operation.
S3
S4
C2
5
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 C1 must be connected to pin 2 of the ICL7660 and ICL7660A and the + terminal of C2 must be connected to GROUND. 5. If the voltage supply driving the ICL7660 and ICL7660A has a large source impedance (25 - 30), then a 2.2µF 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 (pin 3). Device latch up will occur under these conditions. A 1N914 or similar diode placed in parallel with C2 will prevent the device from latching up under these conditions. (Anode pin 5, Cathode pin 3).
VOUT = -VIN 7
FIGURE 12. IDEALIZED NEGATIVE VOLTAGE CONVERTER
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 C1 and C2 are used.
V+ 1 2 10µF + ICL7660 ICL7660A 8 7 6 5
RO
-
3 4
V+ +
VOUT
10µF
+
VOUT = - V+
FIGURE 13A. CONFIGURATION
FIGURE 13B. THEVENIN EQUIVALENT
FIGURE 13. SIMPLE NEGATIVE CONVERTER
3-31
ICL7660, ICL7660A
t2 t1
B 0 V -(V+)
A
FIGURE 14. OUTPUT RIPPLE
V+ 1 2 C1 3 4 ICL7660 ICL7660A "1" 8 7 6 5 C1 1 2 3 4 ICL7660 ICL7660A "n" 8 7 6 5 C2 RL
+
FIGURE 15. PARALLELING DEVICES
V+ 1 2 10µF + ICL7660 ICL7660A "1" 8 7 6 5 10µF + 1 2 ICL7660 ICL7660A "n" 8 7 6 5 10µF + VOUT = - nV+
-
3 4
-
3 4
10µF
+
FIGURE 16. CASCADING DEVICES FOR INCREASED OUTPUT VOLTAGE
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 C1 and C2 , and the ESR (equivalent series resistance) of C1 and C2. A good first order approximation for RO is: RO 2(RSW1 + RSW3 + ESRC1) +
2(RSW2 + RSW4 + ESRC1) +
RO 2(RSW1 + RSW3 + ESRC1) +
1 (fPUMP) (C1) (fPUMP = + ESRC2
fOSC , RSWX = MOSFET switch resistance) 2 Combining the four RSWX terms as RSW, we see that: 1 2 (RSW) + + 4 (ESRC1) + ESRC2 RO (fPUMP) (C1)
RSW, the total switch resistance, is a function of supply voltage and temperature (See the Output Source Resistance graphs), typically 23 at 25oC and 5V. Careful selection of C1 and C2 will 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 > 10µF and there is no longer enough time to fully charge the capacitors
3-32
ICL7660, ICL7660A
every cycle. In a typical application where fOSC = 10kHz and C = C1 = C2 = 10µF: RO 2 (23) +
1 (5 · 103) (10-5) + 4 (ESRC1) + ESRC2
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 (VIN), 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.
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 10. RO 2 (23) +
1 (5 · 103) (10-5) + 4 (ESRC1) + ESRC2
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.
V+ 1 2 10µF + ICL7660 ICL7660A 8 1k 7 6 5 3 4 CMOS GATE V+
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 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 C2 at 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 C2 during time t2 , the half of the cycle when C2 supplies 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:
VRIPPLE
-
+
VOUT 10µF
[
1 2 (fPUMP) (C2) + 2 (ESRC2)
]
IOUT
FIGURE 17. EXTERNAL CLOCKING
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: ROUT =
ROUT (of ICL7660/ICL7660A) n (number of devices)
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 by increasing the values of C1 and C2 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 C1 and C2 (from 10µF to 100µF).
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ICL7660, ICL7660A
V+ 1 2 C1 + ICL7660 ICL7660A 8 7 6 5 COSC + 1 2 C1 ICL7660 ICL7660A 8 7 6 5 VOUT = (2V+) (VFD1) - (VFD2) + V+ VOUT = - (nVIN - VFDX)
D1 +
C3
-
3 4
-
3 4
+
VOUT C2
C2
+
D2
FIGURE 18. LOWERING OSCILLATOR FREQUENCY
-
C4
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 C1 to a voltage level of V+ -VF (where V+ is the supply voltage and VF is the forward voltage drop of diode D1). On the transfer cycle, the voltage on C1 plus the supply voltage (V+) is applied through diode D2 to capacitor C2 . The voltage thus created on C2 becomes (2V+) - (2VF) or twice the supply voltage minus the combined forward voltage drops of diodes D1 and 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 60.
V+ 1 2 3 4 ICL7660 ICL7660A 8 7 6 5 + + C1 D1 D2 VOUT = (2V+) - (2VF)
FIGURE 20. COMBINED NEGATIVE VOLTAGE CONVERTER AND POSITIVE DOUBLER
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).
V+ + RL1 50µF
1 8 ICL7660 ICL7660A 7 6 5 2
VOUT = V+ - V2 RL2 50µF
+
+
3 4
-
-
C2
50µF
V-
FIGURE 19. POSITIVE VOLT DOUBLER
FIGURE 21. SPLITTING A SUPPLY IN HALF
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 C3 perform the pump and reservoir functions respectively for the generation of the negative voltage, while capacitors C2 and C4 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.
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.
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ICL7660, ICL7660A
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".
+8V 56K +8V 50K 100 50K
-
100K
ICL7611
10µF +
+ 1 2 ICL7660 ICL7660A 8 7 6 5 VOUT
ICL8069
100µF
+
-
3 4
800K
250K VOLTAGE ADJUST
100µF +
FIGURE 22. REGULATING THE OUTPUT VOLTAGE
+5V LOGIC SUPPLY 12 TTL DATA INPUT 16 4 15 1 2 + 10µF ICL7660 ICL7660A 8 7 6 5 10µF IH5142 13 14 11 1 3 RS232 DATA OUTPUT +5V -5V
-
3 4
+
FIGURE 23. RS232 LEVELS FROM A SINGLE 5V SUPPLY
All Intersil semiconductor products are manufactured, assembled and tested under ISO9000 quality systems certification.
Intersil semiconductor 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. However, 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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Sales Office Headquarters
NORTH AMERICA Intersil Corporation P. O. Box 883, Mail Stop 53-204 Melbourne, FL 32902 TEL: (407) 724-7000 FAX: (407) 724-7240 EUROPE Intersil SA Mercure Center 100, Rue de la Fusee 1130 Brussels, Belgium TEL: (32) 2.724.2111 FAX: (32) 2.724.22.05 ASIA Intersil (Taiwan) Ltd. 7F-6, No. 101 Fu Hsing North Road Taipei, Taiwan Republic of China TEL: (886) 2 2716 9310 FAX: (886) 2 2715 3029
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