LMC7660
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SNOSBZ9C – APRIL 1997 – REVISED APRIL 2013
LMC7660 Switched Capacitor Voltage Converter
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FEATURES
DESCRIPTION
•
The LMC7660 is a CMOS voltage converter capable
of converting a positive voltage in the range of +1.5V
to +10V to the corresponding negative voltage of
−1.5V to −10V. The LMC7660 is a pin-for-pin
replacement for the industry-standard 7660. The
converter features: operation over full temperature
and voltage range without need for an external diode,
low quiescent current, and high power efficiency.
1
2
•
•
•
•
•
•
•
Operation Over Full Temperature and Voltage
Range without an External Diode
Low Supply Current, 200 μA Max
Pin-for-pin Replacement for the 7660
Wide Operating Range 1.5V to 10V
97% Voltage Conversion Efficiency
95% Power Conversion Efficiency
Easy to Use, Only 2 External Components
Extended Temperature Range
The LMC7660 uses its built-in oscillator to switch 4
power MOS switches and charge two inexpensive
electrolytic capacitors.
Block Diagram
Pin Configuration
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 1997–2013, Texas Instruments Incorporated
LMC7660
SNOSBZ9C – APRIL 1997 – REVISED APRIL 2013
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
ABSOLUTE MAXIMUM RATINGS (1) (2)
Supply Voltage
10.5V
−0.3V to (V+ + 0.3V)
for V+ < 5.5V
Input Voltage on Pin 6, 7 (3)
+
(V − 5.5V) to (V+ + 0.3V)
for V+ > 5.5V
Current into Pin 6
(3)
20 μA
Output Short Circuit
Duration (V+ ≤ 5.5V)
Power Dissipation
Continuous
(4)
PDIP Package
1.4W
SOIC Package
TJ Max
0.6W
(4)
150°C
θJA (4)
PDIP Package
90°C/W
SOIC Package
160°C/W
−65°C ≤ T ≤ 150°C
Storage Temp. Range
Lead Temperature
(Soldering, 5 sec.)
ESD Tolerance
(1)
(2)
(3)
(4)
(5)
260°C
(5)
± 2000V
Absolute Maximum ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not
apply when operating the device beyond its rated operating conditions. See Note (1) under Electrical Characteristics for conditions.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
Connecting any input terminal to voltages greater than V+ or less than ground may cause destructive latchup. It is recommended that no
inputs from sources operating from external supplies be applied prior to “power-up” of the LMC7660.
For operation at elevated temperature, these devices must be derated based on a thermal resistance of θja and Tj max, Tj = TA + θja PD.
The test circuit consists of the human body model of 100 pF in series with 1500Ω.
ELECTRICAL CHARACTERISTICS (1)
Symbol
Parameter
Conditions
Typ
LMC7660IN/
LMC7660IM
Limit
Is
V+H
Supply Current
Supply Voltage
Range High
V+L
(1)
(2)
(3)
2
(3)
RL = ∞
120
RL = 10 kΩ, Pin 6 Open
3 to 10
Voltage Efficiency ≥ 90%
Supply Voltage
RL = 10 kΩ, Pin 6 to Gnd.
Range Low
Voltage Efficiency ≥ 90%
(2)
Units
Limits
200
μA
400
max
3 to 10
V
3 to 10
1.5 to 3.5
1.5 to 3.5
V
1.5 to 3.5
Boldface numbers apply at temperature extremes. All other numbers apply at TA = 25°C, V+ = 5V, Cosc = 0, and apply for the LMC7660
unless otherwise specified. Test circuit is shown in Figure 1 .
Limits at room temperature are specified and 100% production tested. Limits in boldface are specified over the operating temperature
range (but not 100% tested), and are not used to calculate outgoing quality levels.
The LMC7660 can operate without an external diode over the full temperature and voltage range. The LMC7660 can also be used with
the external diode Dx, when replacing previous 7660 designs.
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ELECTRICAL CHARACTERISTICS(1) (continued)
Symbol
Parameter
Conditions
Typ
LMC7660IN/
LMC7660IM
Limit
Rout
Output Source
IL = 20 mA
55
V = 2V, IL = 3 mA
110
Resistance
Pin 6 Short to Gnd.
Fosc
Oscillator
(2)
Units
Limits
100
Ω
120
max
200
Ω
300
max
10
kHz
Frequency
Peff
Power Efficiency
RL = 5 kΩ
Vo
Voltage Conversion
RL = ∞
eff
97
99.9
Efficiency
Iosc
Oscillator Sink or
Pin 7 = Gnd. or V+
95
%
90
min
97
%
95
min
3
μA
Source Current
Figure 1. LMC7660 Test Circuit
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TYPICAL PERFORMANCE CHARACTERISTICS
4
OSC Freq.
vs
OSC
Capacitance
Vout
vs
Iout @ V+ = 2V
Figure 2.
Figure 3.
Vout
vs
Iout @ V+ = 5V
Supply Current & Power Efficiency
vs Load Current (V+ = 2V)
Figure 4.
Figure 5.
Supply Current & Power Efficiency
vs Load Current (V+ = 5V)
Output Source Resistiance as a
Function of Temperature
Figure 6.
Figure 7.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Unloaded Oscillator Frequency
as a Function of Temperature
Output R
vs
Supply Voltage
Figure 8.
Figure 9.
Peff
vs
OSC Freq. @ V+ = 5V
Figure 10.
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APPLICATION INFORMATION
CIRCUIT DESCRIPTION
The LMC7660 contains four large CMOS switches which are switched in a sequence to provide supply inversion
Vout = −Vin. Energy transfer and storage are provided by two inexpensive electrolytic capacitors. Figure 11 shows
how the LMC7660 can be used to generate −V+ from V+. When switches S1 and S3 are closed, Cp charges to
the supply voltage V+. During this time interval, switches S2 and S4 are open. After Cp charges to V+, S1 and S3
are opened, S2 and S4 are then closed. By connecting S2 to ground, Cp develops a voltage −V+/2 on Cr. After a
number of cycles Cr will be pumped to exactly −V+. This transfer will be exact assuming no load on Cr, and no
loss in the switches.
In the circuit of Figure 11, S1 is a P-channel device and S2, S3, and S4 are N-channel devices. Because the
output is biased below ground, it is important that the p− wells of S3 and S4 never become forward biased with
respect to either their sources or drains. A substrate logic circuit specifies that these p− wells are always held at
the proper voltage. Under all conditions S4 p− well must be at the lowest potential in the circuit. To switch off S4,
a level translator generates VGS4 = 0V, and this is accomplished by biasing the level translator from the S4 p−
well.
An internal RC oscillator and ÷ 2 circuit provide timing signals to the level translator. The built-in regulator biases
the oscillator and divider to reduce power dissipation on high supply voltage. The regulator becomes active at
about V+ = 6.5V. Low voltage operation can be improved if the LV pin is shorted to ground for V+ ≤ 3.5V. For V+
≥ 3.5V, the LV pin must be left open to prevent damage to the part.
POWER EFFICIENCY AND RIPPLE
It is theoretically possible to approach 100% efficiency if the following conditions are met:
1. The drive circuitry consumes little power.
2. The power switches are matched and have low Ron.
3. The impedance of the reservoir and pump capacitors are negligibly small at the pumping frequency.
The LMC7660 closely approaches 1 and 2 above. By using a large pump capacitor Cp, the charge removed
while supplying the reservoir capacitor is small compared to Cp's total charge. Small removed charge means
small changes in the pump capacitor voltage, and thus small energy loss and high efficiency. The energy loss by
Cp is:
(1)
By using a large reservoir capacitor, the output ripple can be reduced to an acceptable level. For example, if the
load current is 5 mA and the accepted ripple is 200 mV, then the reservoir capacitor can omit approximately be
calculated from:
(2)
PRECAUTIONS
1.
2.
3.
4.
Do not exceed the maximum supply voltage or junction temperature.
Do not short pin 6 (LV terminal) to ground for supply voltages greater than 3.5V.
Do not short circuit the output to V+.
External electrolytic capacitors Cr and Cp should have their polarities connected as shown in Figure 1.
REPLACING PREVIOUS 7660 DESIGNS
To prevent destructive latchup, previous 7660 designs require a diode in series with the output when operated at
elevated temperature or supply voltage. Although this prevented the latchup problem of these designs, it lowered
the available output voltage and increased the output series resistance.
The TI LMC7660 has been designed to solve the inherent latch problem. The LCM7660 can operate over the
entire supply voltage and temperature range without the need for an output diode. When replacing existing
designs, the LMC7660 can be operated with diode Dx.
6
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Figure 11. Idealized Voltage Converter
TYPICAL APPLICATIONS
CHANGING OSCILLATOR FREQUENCY
It is possible to dramatically reduce the quiescent operating current of the LMC7660 by lowering the oscillator
frequency. The oscillator frequency can be lowered from a nominal 10 kHz to several hundred hertz, by adding a
slow-down capacitor Cosc (Figure 12). As shown in the Typical Performance Curves the supply current can be
lowered to the 10 μA range. This low current drain can be extremely useful when used in μPower and battery
back-up equipment. It must be understood that the lower operating frequency and supply current cause an
increased impedance of Cr and Cp. The increased impedance, due to a lower switching rate, can be offset by
raising Cr and Cp until ripple and load current requirements are met.
SYNCHRONIZING TO AN EXTERNAL CLOCK
Figure 13 shows an LMC7660 synchronized to an external clock. The CMOS gate overrides the internal oscillator
when it is necessary to switch faster or reduce power supply interference. The external clock still passes through
the ÷2 circuit in the 7660, so the pumping frequency will be ½ the external clock frequency.
Figure 12. Reduce Supply Current by Lowering Oscillator Frequency
Figure 13. Synchronizing to an External Clock
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LOWERING OUTPUT IMPEDANCE
Paralleling two or more LMC7660's lowers output impedance. Each device must have it's own pumping capacitor
Cp, but the reservoir capacitor Cr is shared as depicted in Figure 14. The composite output resistance is:
(3)
INCREASING OUTPUT VOLTAGE
Stacking the LMC7660s is an easy way to produce a greater negative voltage. It should be noted that the input
current required for each stage is twice the load current on that stage as shown in Figure 15. The effective output
resistance is approximately the sum of the individual Rout values, and so only a few levels of multiplication can be
used.
It is possible to generate −15V from +5V by connecting the second 7660's pin 8 to +5V instead of ground as
shown in Figure 16. Note that the second 7660 sees a full 20V and the input supply should not be increased
beyond +5V.
Figure 14. Lowering Output Resistance by Paralleling Devices
Figure 15. Higher Voltage by Cascade
Figure 16. Getting −15V from +5V
8
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SPLIT V+ IN HALF
Figure 17 is one of the more interesting applications for the LMC7660. The circuit can be used as a precision
voltage divider (for very light loads), alternately it is used to generate a ½ supply point in battery applications. In
the ½ cycle when S1 and S3 are closed, the supply voltage divides across the capacitors in a conventional way
proportional to their value. In the ½ cycle when S2 and S4 are closed, the capacitors switch from a series
connection to a parallel connection. This forces the capacitors to have the same voltage; the charge redistributes
to maintain precisely V+/2, across Cp and Cr. In this application all devices are only V+/2, and the supply voltage
can be raised to 20V giving exactly 10V at Vout.
GETTING UP … AND DOWN
The LMC7660 can also be used as a positive voltage multiplier. This application, shown in Figure 18, requires 2
additional diodes. During the first ½ cycle S2 charges Cp1 through D1; D2 is reverse biased. In the next ½ cycle
S2 is open and S1 is closed. Since Cp1 is charged to V+ − VD1 and is referenced to V+ through S1, the junction of
D1 and D2 is at V+ + (V+ −VD1). D1 is reverse biased in this interval. This application uses only two of the four
switches in the 7660. The other two switches can be put to use in performing a negative conversion at the same
time as shown in Figure 19. In the ½ cycle that D1 is charging Cp1, Cp2 is connected from ground to −Vout via S2
and S4, and Cr2 is storing Cp2's charge. In the interval that S1 and S3 are closed, Cp1 pumps the junction of D1
and D2 above V+, while Cp2 is refreshed from V+.
Figure 17. Split V+ in Half
Figure 18. Positive Voltage Multiplier
Figure 19. Combined Negative Converter and Positive Multiplier
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THERMOMETER SPANS 180°C
Using the combined negative and positive multiplier of Figure 20 with an LM35 it is possible to make a μPower
thermometer that spans a 180°C temperature range. The LM35 temperature sensor has an output sensitivity of
10 mV/°C, while drawing only 50 μA of quiescent current. In order for the LM35 to measure negative
temperatures, a pull down to a negative voltage is required. Figure 20 shows a thermometer circuit for measuring
temperatures from −55°C to +125°C and requiring only two 1.5V cells. End of battery life can be extended by
replacing the up converter diodes with Schottky's.
REGULATING −VOUT
It is possible to regulate the output of the LMC7660 and still maintain μPower performance. This is done by
enclosing the LMC7660 in a loop with a LP2951. The circuit of Figure 21 will regulate Vout to −5V for IL = 10 mA,
and Vin = 6V. For Vin > 7V, the output stays in regulation up to IL = 25 mA. The error flag on pin 5 of the LP2951
sets low when the regulated output at pin 4 drops by about 5%. The LP2951 can be shutdown by taking pin 3
high; the LMC7660 can be shutdown by shorting pin 7 and pin 8.
The LP2951 can be reconfigured to an adjustable type regulator, which means the LMC7660 can give a
regulated output from −2.0V to −10V dependent on the resistor ratios R1 and R2, as shown in Figure 22, Vref =
1.235V:
(4)
*For lower voltage operation, use Schottky rectifiers
Figure 20. μPower Thermometer Spans 180°C, and Pulls Only 150 μA
Figure 21. Regulated −5V with 200 μA Standby Current
10
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Vref = 1.235V
*Low voltage operation
Figure 22. LMC7660 and LP2951 Make a Negative Adjustable Regulator
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REVISION HISTORY
Changes from Revision B (April 2013) to Revision C
•
12
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 11
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PACKAGE OPTION ADDENDUM
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26-Aug-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
LMC7660IM
NRND
SOIC
D
8
95
Non-RoHS
& Green
Call TI
Level-1-235C-UNLIM
LMC76
60IM
LMC7660IM/NOPB
ACTIVE
SOIC
D
8
95
RoHS & Green
SN
Level-1-260C-UNLIM
LMC7660IMX
NRND
SOIC
D
8
2500
Non-RoHS
& Green
Call TI
Level-1-235C-UNLIM
LMC7660IMX/NOPB
ACTIVE
SOIC
D
8
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
LMC76
60IM
Samples
LMC7660IN/NOPB
ACTIVE
PDIP
P
8
40
RoHS & Green
NIPDAU
Level-1-NA-UNLIM
-40 to 85
LMC
7660IN
Samples
-40 to 85
LMC76
60IM
LMC76
60IM
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of