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MC7660 Charge Pump DC-to-DC Voltage Converter
The MC7660 is a pin-compatible replacement for the Industry standard ICL7660 charge pump voltage converter. It converts a +1.5V to +10V input to a corresponding -1.5V to -10V output using only two low-cost capacitors, eliminating inductors and their associated cost, size and EMI. The on-board oscillator operates at a nominal frequency of 10kHz. Operation below 10kHz (for lower supply current applications) is possible by connecting an external capacitor from OSC to ground (with pin 1 open). The MC7660 is available in an 8-pin SOIC package in extended temperature range. Features Converts +5V Supply to -5V Supply Wide Input Voltage Range: 1.5V to 10V Efficient Voltage Conversion: 99.9% Excellent Power Efficiency: 98% Low Power Supply: 80A @ 5VIN Low Cost and Easy to Use - Only Two External Capacitors Required * Available in Small Outline (SO) Package * ESD Protection: 2.5kV * No Dx Diode Required for High Voltage Operation
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SO-8 D SUFFIX CASE 751
* * * * * *
PIN CONFIGURATION (Top View)
NC 1 CAP+ 2 GND 3 CAP- 4
8 V+ 7 OSC 6 LV 5 VOUT
ORDERING INFORMATION
Typical Applications * RS-232 Negative Bias * Display Bias * Data Aquisition Negative Supply Generation
Device MC7660DR2
Package 8-Pin SOIC
Shipping 2500 Tape/Reel
FUNCTIONAL BLOCK DIAGRAM
V+ CAP+ 8 2
OSC LV
7 6
RC OSCILLATOR
B2
VOLTAGE- LEVEL TRANSLATOR
4
CAP-
5 INTERNAL VOLTAGE REGULATOR
VOUT
MC7660
3 GND
LOGIC NETWORK
(c) Semiconductor Components Industries, LLC, 1999
1
February, 2000 - Rev. 2
Publication Order Number: MC7660/D
MC7660
ABSOLUTE MAXIMUM RATINGS*
Parameter Supply Voltage LV and OSC Inputs Voltage (Note 1.) V+ < 5.5V V+ > 5.5V Current Into LV (Note 1.) V+ > 3.5V Output Short Duration (VSUPPLY 5.5V) Power Dissipation (TA 70C) Derate above 50C Operating Temperature Range -40 to +85 Storage Temperature Range Lead Temperature (Soldering, 10 Seconds) -65 to +150 +300 C C Value +10.5 -0.3 to (V+ + 0.3) (V+ - 5.5) to (V+ + 0.3) 20 Continuous 470 5.5 mW mW/C C A Unit V V
* Maximum Ratings are those values beyond which damage to the device may occur. 1. Connecting any input terminal to voltages greater than V+ or less than GND may cause destructive latch-up. It is recommended that no inputs from sources operating from external supplies be applied prior to "power up" of the MC7660.
ELECTRICAL CHARACTERISTICS (Specifications Measured Over Operating Temperature Range, V+ = 5V, COSC = 0, Test Circuit (Figure 1), unless otherwise noted.
Symbol I+ V+H V+L ROUT Supply Current (RL =
R)
Characteristic
Min -- 3.0 1.5 -- -- -- -- -- 95 97 -- -- IS
Typ 80 -- -- 70 -- -- 150 10 98 99.9 1000 100
Max 180 10
Unit A V V
Supply Voltage Range, High (-40C TA +85C, RL = 10 kW, LV Open) Supply Voltage Range, Low (-40C TA +85C, RL = 10 kW, LV to GND) Output Source Resistance IOUT = 20mA, TA = 25C IOUT = 20mA, 0C TA +70C IOUT = 20mA, -40C TA +85C V+ =2V, IOUT = 3 mA, LV to GND, 0C TA +70C Oscillator Frequency (Pin 7 Open) Power Efficiency (RL = 5kW) Voltage Conversion Efficiency Oscillator Impedance V+ = 2V V+ = 5V
3.5 100 120 130 300 -- -- -- -- --
W
FOSC PEFF VOUT EFF ZOSC
kHz % % kW
1
8
C1 10 mF
+
2 3 4
MC7660
7 6 5
COSC*
IL V+ (+6 V) RL VO
+
*NOTE:
C2 10 mF
For large values of COSC (>1000 pF), the values of C1 and C2 should be increased to 100 mF.
Figure 1. MC7660 Test Circuit
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MC7660
APPLICATIONS INFORMATION
Detailed Description
The MC7660 contains all the necessary circuitry to implement a voltage inverter, with the exception of two external capacitors, which may be inexpensive 10 F polarized electrolytic capacitors. Operation is best understood by considering Figure 2, which shows an idealized voltage inverter. 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.
S1 V+ S2
can, however, degrade operation at low voltages. To improve low-voltage operation, the LV pin should be connected to GND, disabling the regulator. For supply voltages greater than 3.5V, the LV terminal must be left open to ensure latch-up-proof operation and prevent device damage.
Theoretical Power Efficiency Considerations
In theory, a capacitive charge pump can approach 100% efficiency if certain conditions are met: (1) The drive 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 MC7660 approaches these conditions for negative voltage multiplication if large values of C1 and 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 = 1/2 C1 (V12 -- V22) 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 2), compared to the value of RL, there will be a substantial difference in 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.
Dos and Don'ts
C1 C2 VOUT = -VIN
GND
S3
S4
Figure 2. Idealized Charge Pump Inverter
The four switches in Figure 2 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 will result in high power losses and probable device latch-up. This problem is eliminated in the MC7660 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. The voltage regulator portion of the MC7660 is an integral part of the anti-latch-up circuitry. Its inherent voltage drop
* Do not exceed maximum supply voltages. * Do not connect LV terminal to GND for supply voltages greater than 3.5V. * Do not short circuit the output to V+ supply for voltages above 5.5V for extended periods; however, transient conditions including start-up are okay. * When using polarized capacitors in the inverting mode, the + terminal of C1 must be connected to pin 2 of the MC7660 and the + terminal of C2 must be connected to GND Pin 3.
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MC7660
Simple Negative Voltage Converter
V+
1 8
Figure 3 shows typical connections to provide a negative supply where a positive supply is available. A similar scheme may be employed for supply voltages anywhere in the operating range of +1.5V to +10V, keeping in mind that pin 6 (LV) is tied to the supply negative (GND) only for supply voltages below 3.5V. The output characteristics of the circuit in Figure 3 are those of a nearly ideal voltage source in series with 70W. Thus, for a load current of -10mA and a supply voltage of +5V, the output voltage would be -4.3V. The dynamic output impedance of the MC7660 is due, primarily, to capacitive reactance of the charge transfer capacitor (C1). Since this capacitor is connected to the output for only 1/2 of the cycle, the equation is: XC
VOUT C2 10 mF
C1 10 mF
+
2 3 4
MC7660
7 6 5
+
Figure 3. Simple Negative Converter Parallel Devices
1 where f = 10kHz and C1 = 10F.
+ 2pf2C + 3.18W,
V+
1 2 8
Any number of MC7660 voltage converters may be paralleled to reduce output resistance (Figure 4). The reservoir capacitor, C2, serves all devices, while each device requires its own pump capacitor, C1. The resultant output resistance would be approximately: R OUT OUT (of MC7660) + nR(number of devices)
C1
MC7660
7 6 5
1 2
8
3 4
MC7660
7 6 5
RL
C1
3 4
+
C2
Figure 4. Paralleling Devices Lowers Output Impedance Cascading Devices
The MC7660 may be cascaded as shown (Figure 5) to produce 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 MC7660 ROUT values.
Changing the MC7660 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 6. In order to prevent possible device latch-up, a 1kW 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 10kW pull-up 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 MC7660 at low load levels by lowering the oscillator frequency. This reduces the switching losses, and is achieved by connecting an additional capacitor, COSC, as shown in Figure 7. Lowering the oscillator frequency will cause an undesirable increase in the impedance of the pump (C1) and the reservoir (C2) capacitors. To overcome this, increase 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 pin 8 (V+) will lower the oscillator frequency to 1kHz from its nominal frequency of 10kHz (a multiple of 10), and necessitate a corresponding increase in the values of C1 and C2 (from 10F to 100F).
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MC7660
V+
1 8
10 mF
+
2 3 4
MC7660 "1"
7 6 5
1
8
10 mF
+
2 3 4
MC7660 "n"
7 6 5
VOUT* + 10 mF
*NOTE:
VOUT = -n V+ for 1.5 V V+ 10 V
Figure 5. Increased Output Voltage by Cascading Devices
V+
1 8
V+
1 8
V+ VOUT = (2 V+) - (2 VF) + C2
1 kW
10 mF
+
2 3 4
MC7660
7 6 5
CMOS GATE VOUT + 10 mF
2 3 4
MC7660
7 6 5
D1 +
D2 C1
Figure 6. External Clocking
V+
1 8
Figure 8. Positive Voltage Multiplier Combined Negative Voltage Conversion and Positive Supply Multiplication
+ C1
2 3 4
MC7660
7 6 5
COSC
VOUT + C2
Figure 7. Lowering Oscillator Frequency Positive Voltage Multiplication
The MC7660 may be employed to achieve positive voltage multiplication using the circuit shown in Figure 8. In this application, the pump inverter switches of the MC7660 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 (2 V+) - (2 VF), 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 10 mA, it will be approximately 60W.
Figure 9 combines the functions shown in Figures 3 and 8 to provide negative voltage conversion and positive voltage multiplication 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 multiplied 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.
V+
1 2 3 8
VOUT = -(V+ - VF) C3
MC7660
7 6 5
D1 +
+ C1
4
+ C2
D2 +
VOUT = (2 V+) - (2 VF) C4
Figure 9. Combined Negative Converter and Positive Muliplier
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MC7660
Efficient Positive Voltage Multiplication/Conversion
Since the switches that allow the charge pumping operation are bidirectional, the charge transfer can be performed backwards as easily as forwards. Figure 10 shows a MC7660 transforming -5V to +5V (or +5V to +10V, etc.). The only problem here is that the internal clock and
switch-drive section will not operate until some positive voltage has been generated. An initial inefficient pump, as shown in Figure 9, could be used to start this circuit up, after which it will bypass the other (D1 and D2 in Figure 9 would never turn on), or else the diode and resistor shown dotted in Figure 10 can be used to "force" the internal regulator on.
VOUT = -V-
1 8
+ 1 MW
+ C1 10 mF
2 3 4
MC7660
7 6 5
10 mF
V- INPUT
Figure 10. Positive Voltage Conversion Voltage Splitting
The same bidirectional characteristics used in Figure 10 can also be used to split a higher supply in half, as shown in Figure 11. The combined load will be evenly shared between the two sides. Once again, a high value resistor to the LV pin ensures start-up. Because the switches share the load in
50 mF V)
-
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 5, +15V can be converted (via +7.5V and -7.5V) to a nominal -15V, though with rather high series resistance (~250W).
+
1 8
V+
RL1 V + *V OUT 2 RL2 50 mF + -
2 3
MC7660
7 6 5
1 MW
100 kW 100 kW 50 mF + -
4
V-
Figure 11. Splitting a Supply in Half
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MC7660
TYPICAL PERFORMANCE CHARACTERISTICS
12 SUPPLY VOLTAGE (VOLTS) POWER CONVERSION EFFICIENCY (%) 10 8 6 4 2 0 -55 SUPPLY VOLTAGE RANGE 100 98 96 94 92 90 88 86 84 82 80 -25 0 25 50 75 TEMPERATURE (C) 100 125 100 TA = +25C V+ = +5 V 1k OSCILLATOR FREQUENCY (Hz) 10 k IOUT = 15 mA IOUT = 1 mA
Figure 12. Operating Voltage versus Temperature
OUTPUT SOURCE RESISTANCE ( W ) 10 k TA = +25C 1k OUTPUT SOURCE RESISTANCE ( W ) 350 300 250 200 150 100 50 0 -55
Figure 13. Power Conversion Efficiency versus Oscillator Frequency
IOUT = 1 mA
100
V+ = +2 V V+ = +5 V
10 0 1 5 2 3 4 6 SUPPLY VOLTAGE (VOLTS) 7 8
-25
0
25 50 75 TEMPERATURE (C)
100
125
Figure 14. Output Source Resistance versus Supply Voltage
Figure 15. Output Source Resistance versus Temperature
OSCILLATOR FREQUENCY (kHz)
10 k OSCILLATOR FREQUENCY (Hz) TA = +25C V+ = +5 V 1k
20 18 16 14 12 10 8 6 -55
V+ = +5 V
100
10 1 10 100 1000 OSCILLATOR CAPACITANCE (pF) 10 k
-25
0
25 50 75 TEMPERATURE (C)
100
125
Figure 16. Frequency of Oscillation versus Oscillator Capacitance
Figure 17. Unloaded Oscillator Frequency versus Temperature
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MC7660
TYPICAL CHARACTERISTICS (Cont.)
0 OUTPUT VOLTAGE (VOLTS) OUTPUT VOLTAGE (VOLTS) -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 0 10 20 TA = +25C LV OPEN 80 30 40 50 60 70 OUTPUT CURRENT (mA) 90 100 5 4 3 2 1 0 -1 -2 -3 -4 -5 0 10 20 SLOPE 55 W 30 40 50 60 LOAD CURRENT (mA) 70 80 TA = +25C V+ = +5 V
Figure 18. Output Voltage versus Output Current
POWER CONVERSION EFFICIENCY (%) 100 90 80 70 60 50 40 30 20 10 0 0 1.5 3.0 4.5 6.0 LOAD CURRENT (mA) 7.5 9.0 TA = +25C V+ = +2 V POWER CONVERSION EFFICIENCY (%) 20 18 SUPPLY CURRENT (mA) 16 14 12 10 8 6 4 2 0 100 90 80 70 60 50 40 30 20 10 0 0
Figure 19. Output Voltage versus Load Current
100 90 SUPPLY CURRENT (mA) 80 70 60 50 40 30 TA = +25C V+ = +5 V 10 20 30 40 LOAD CURRENT (mA) 50 60 20 10 0
Figure 20. Supply Current and Power Conversion Efficiency versus Load Current
Figure 21. Supply Current and Power Conversion Efficiency versus Load Current
2 OUTPUT VOLTAGE (VOLTS) TA = +25C V+ = +2 V
1
0
-1 SLOPE 150 W -2 0 1 2 3 4 5 6 LOAD CURRENT (mA) 7 8
Figure 22. Output Voltage versus Load Current
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MC7660
PACKAGE DIMENSIONS
8-Pin SOIC PLASTIC PACKAGE CASE 751-06 ISSUE T
A
8
D
5
C
E
1 4
H
0.25
M
B
M
h B C e A
SEATING PLANE
X 45 _
NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994. 2. DIMENSIONS ARE IN MILLIMETER. 3. DIMENSION D AND E DO NOT INCLUDE MOLD PROTRUSION. 4. MAXIMUM MOLD PROTRUSION 0.15 PER SIDE. 5. DIMENSION B DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.127 TOTAL IN EXCESS OF THE B DIMENSION AT MAXIMUM MATERIAL CONDITION. DIM A A1 B C D E e H h L MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 4.80 5.00 3.80 4.00 1.27 BSC 5.80 6.20 0.25 0.50 0.40 1.25 0_ 7_
q
L 0.10 A1 B 0.25
M
CB
S
A
S
q
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MC7660
Notes
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MC7660
Notes
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MC7660
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MC7660/D

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