________________General Description
The MAX680/MAX681 are monolithic, CMOS, dual
charge-pump voltage converters that provide ±10V out-
puts from a +5V input voltage. The MAX680/MAX681 pro-
vide both a positive step-up charge pump to develop
+10V from +5V input and an inverting charge pump to
generate the -10V output. Both parts have an on-chip,
8kHz oscillator. The MAX681 has the capacitors internal to
the package, and the MAX680 requires four external
capacitors to produce both positive and negative voltages
from a single supply.
The output source impedances are typically 150Ω, pro-
viding useful output currents up to 10mA. The low quies-
cent current and high efficiency make this device suitable
for a variety of applications that need both positive and
negative voltages generated from a single supply.
The MAX864/MAX865 are also recommended for new
designs. The MAX864 operates at up to 200kHz and uses
smaller capacitors. The MAX865 comes in the smaller
µMAX package.
________________________Applications
The MAX680/MAX681 can be used wherever a single
positive supply is available and where positive and nega-
tive voltages are required. Common applications include
generating ±6V from a 3V battery and generating ±10V
from the standard +5V logic supply (for use with analog
circuitry
)
. Typical applications include:
____________________________Features
♦95% Voltage-Conversion Efficiency
♦85% Power-Conversion Efficiency
♦+2V to +6V Voltage Range
♦Only Four External Capacitors Required (MAX680)
♦No Capacitors Required (MAX681)
♦500µA Supply Current
♦Monolithic CMOS Design
MAX680/MAX681
+5V to ±10V Voltage Converters
________________________________________________________________
Maxim Integrated Products
1
VCC
C2-
GND
V-
1
2
8
7
V+
C1+
C2+
C1-
MAX680
DIP/SO
TOP VIEW
3
4
6
5
14
13
12
11
10
9
8
1
2
3
4
5
6
7
VCC
VCC
VCC
VCC
C2+
C1-
C1-
V+
MAX681
V+
GND
GND
V-
C2-
C2-
DIP
_________Typical Operating Circuits
MAX680
+10V
4.7µF
4.7µF
4.7µF
4.7µF-10V
GND
+10V
-10V
GND
FOUR PINS REQUIRED
(MAX681 ONLY)
+5V
GND
GND
+5V
C1-
C1+ V-
V+
C2-
VCC
GND
+5V to ±10V CONVERTER
MAX681
V-
V+
VCC
GND
C1+
_________________Pin Configurations
19-0896; Rev 1; 7/96
PART
MAX680CPA
MAX680CSA
MAX680C/D 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 Plastic DIP
8 Narrow SO
Dice
_______________Ordering Information
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX680EPA
MAX680ESA -40°C to +85°C
-40°C to +85°C 8 Plastic DIP
8 Narrow SO
MAX680MJA -55°C to +125°C 8 CERDIP
MAX681CPD
MAX681EPD -40°C to +85°C
0°C to +70°C 14 Plastic DIP
14 Plastic DIP
±6V from 3V Lithium Cell
Hand-Held Instruments
Data-Acquisition Systems
Panel Meters
±10V from +5V Logic
Supply
Battery-Operated
Equipment
Operational Amplifier
Power Supplies
MAX680/MAX681
+5V to ±10V Voltage Converters
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +5V, test circuit Figure 1, TA= +25°C, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VCC ................................................................................... +6.2V
V+ ...................................................................................... +12V
V- ..........................................................................................-12V
V- Short-Circuit Duration ...........................................Continuous
V+ Current ..........................................................................75mA
VCC ∆V/∆T ..........................................................................1V/µs
Continuous Power Dissipation (TA = +70°C)
8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) .....727mW
8-Pin Narrow SO (derate 5.88mW/°C above +70°C) .....471mW
8-Pin CERDIP (derate 8.00mW/°C above +70°C) ..........640mW
14-Pin Plastic DIP (derate 10.00mW/°C above +70°C) ...800mW
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
kHz
48Oscillator Frequency
Positive Charge-Pump
Output Source Resistance
2.5
12
0.5 1
400
350
180 300
3
3
Supply Current mA
2.0 1.5 to 6.0 6.0Supply-Voltage Range
150 250
MIN TYP MAX
VCC = 5V, 0°C ≤TA≤+70°C, RL= ∞
VCC = 3V, TA= +25°C, RL= ∞
VCC = 5V, TA= +25°C, RL= ∞
IL+ = 10mA,
IL- = 0mA,
VCC = 5V
IL+ = 5mA, IL- = 0mA, VCC = 2.8V,
TA= +25°C
VCC = 5V, -40°C ≤TA≤+85°C, RL= ∞
VCC = 5V, -55°C ≤TA≤+125°C, RL= ∞
MIN ≤TA≤MAX, RL= 10kΩ
IL+ = 10mA, IL- = 0mA, VCC = 5V,
TA= +25°C
CONDITIONS UNITSPARAMETER
V+, RL= ∞
RL= 10kΩ95 99 %85Power Efficiency
IL- = 10mA,
IL+ = 0mA,
V+ = 10V
IL- = 5mA, IL+ = 0mA, V+ = 5.6V,
TA= +25°C
IL- = 10mA, IL+ = 0mA, V+ = 10V,
TA= +25°C
Ω
Negative Charge-Pump
Output Source Resistance
250
200
110 175
90 150
V-, RL= ∞%
90 97
Voltage-Conversion
Efficiency
V
Ω
325
200
0°C ≤TA≤+70°C
-40°C ≤TA≤+85°C
-55°C ≤TA≤+125°C
0°C ≤TA≤+70°C
-40°C ≤TA≤+85°C
-55°C ≤TA≤+125°C
MAX680/MAX681
+5V to ±10V Voltage Converters
_______________________________________________________________________________________
3
02.0
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
MAX680/681-TOC1
V (V)
OUTPUT RESISTANCE (Ω)
50
100
150
200
250
3.0 4.0 5.0 6.0
ROUT-
ROUT+
C1-C4 = 10µF
40
OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX680/681-TOC2
LOAD CURRENT ( A)
|VOUT| (V)
5
6
7
8
9
10
510 15 20
V+ vs. IL+
IL- = 0
V- vs. IL+
IL- = 0
V+ vs. IL-
IL+ = 0
V- vs. IL-
IL+ = 0
02.0
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX680/681-TOC3
V (V)
SUPPLY CURRENT (mA)
0.5
1.0
1.5
2.0
3.0 4.0 5.0 6.0
RL = ∞
401234 6789
OUTPUT VOLTAGE vs. OUTPUT CURRENT
(FROM V+ TO V-)
MAX680/681-TOC4
OUTPUT CURRENT (mA)
|VOUT| (V)
5
6
7
8
9
10
510
C1–C4 = 10µF
V-
V+
MAX680, MAX681
0-50
OUTPUT SOURCE RESISTANCE
vs. TEMPERATURE
MAX680/681-TOC5
TEMPERATURE (°C)
OUTPUT SOURCE RESISTANCE (Ω)
50
100
150
200
-25 0 25 50 75 100 125
ROUT+
ROUT-
VCC = 5V
0
OUTPUT RIPPLE vs.
OUTPUT CURRENT (IL+ OR IL-)
MAX681/681-TOC6
OUTPUT CURRENT (mA)
OUTPUT RIPPLE (mVp-p)
50
100
150
200
510 15 20
V+ AND V-
V-
V-
MAX681
VCC = 5V
V+
MAX680
C3, C4 = 100µF
MAX680
C3, C4 = 10µF
0
V+
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX680/MAX681
+5V to ±10V Voltage Converters
4 _______________________________________________________________________________________
_______________Detailed Description
The MAX681 contains all circuitry needed to implement
a dual charge pump. The MAX680 needs only four
capacitors. These may be inexpensive electrolytic
capacitors with values in the 1µF to 100µF range. The
MAX681 contains two 1.5µF capacitors as C1 and C2,
and two 2.2µF capacitors as C3 and C4. See
Typical
Operating Characteristics.
Figure 2a shows the idealized operation of the positive
voltage converter. The on-chip oscillator generates a
50% duty-cycle clock signal. During the first half of the
cycle, switches S2 and S4 are open, S1 and S3 are
closed, and capacitor C1 is charged to the input volt-
age VCC. During the second half-cycle, S1 and S3 are
open, S2 and S4 are closed, and C1 is translated
upward by VCC volts. Assuming ideal switches and no
load on C3, charge is transferred onto C3 from C1 such
that the voltage on C3 will be 2VCC, generating the
positive supply.
Figure 2b shows the negative converter. The switches
of the negative converter are out of phase from the pos-
itive converter. During the second half of the clock
cycle, S6 and S8 are open and S5 and S7 are closed,
charging C2 from V+ (pumped up to 2VCC by the posi-
tive charge pump) to GND. In the first half of the clock
IL+
RL+
RL-
IL-
MAX680
C1
4.7µF
VCC IN
C3
10µF
V+ OUT
V- OUT
GND
C4
10µF
C2
4.7µF
C1- 8
7
6
5
C2+
V-
V+
1
2
3
4
C1+
VCC
GND
C2-
VCC
a) b)
S1
S3
8kHz
C1+
C1 C3
C1-
S2
S4
S5 S6
S7 S8
C2-
GND
V-
RL-
RL+
C2+
C4
C2
GNDVCC
IL-
V+
GND
IL+
V+
Figure 1. Test Circuit
Figure 2. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump
cycle, S5 and S7 are open, S6 and S8 are closed, and
the charge on C2 is transferred to C4, generating the
negative supply. The eight switches are CMOS power
MOSFETs. S1, S2, S4, and S5 are P-channel
switches, while S3, S6, S7, and S8 are N-channel
switches.
__________Efficiency Considerations
Theoretically, a charge-pump voltage multiplier can
approach 100% efficiency under the following con-
ditions:
• The charge-pump switches have virtually no offset
and extremely low on-resistance
• Minimal power is consumed by the drive circuitry
• The impedances of the reservoir and pump capaci-
tors are negligible
For the MAX680/MAX681, the energy loss per clock
cycle is the sum of the energy loss in the positive and
negative converters as below:
LOSSTOT = LOSSPOS + LOSSNEG
=1⁄2C1 [(V+)2– (V+)(VCC)] +
1⁄2C2 [(V+)2– (V-)2]
There will be a substantial voltage difference between
(V+ - VCC) and VCC for the positive pump, and
between V+ and V-, if the impedances of pump capaci-
tors C1 and C2 are high relative to their respective out-
put loads.
Larger C3 and C4 reservoir capacitor values reduce
output ripple. Larger values of both pump and reservoir
capacitors improve efficiency.
________Maximum Operating Limits
The MAX680/MAX681 have on-chip zener diodes that
clamp VCC to approximately 6.2V, V+ to 12.4V, and
V- to -12.4V. Never exceed the maximum supply volt-
age: excessive current may be shunted by these
diodes, potentially damaging the chip. The MAX680/
MAX681 operate over the entire operating temperature
range with an input voltage of +2V to +6V.
________________________Applications
Positive and Negative Converter
The most common application of the MAX680/MAX681
is as a dual charge-pump voltage converter that pro-
vides positive and negative outputs of two times a posi-
tive input voltage. For applications where PC board
space is at a premium, the MAX681, with its capacitors
internal to the package, offers the smallest footprint.
The simple circuit shown in Figure 3 performs the same
function using the MAX680 with external capacitors C1
and C3 for the positive pump and C2 and C4 for the
negative pump. In most applications, all four capacitors
are low-cost, 10µF or 22µF polarized electrolytics.
When using the MAX680 for low-current applications,
1µF can be used for C1 and C2 charge-pump capaci-
tors, and 4.7µF for C3 and C4 reservoir capacitors.
C1 and C3 must be rated at 6V or greater, and C2 and
C4 must be rated at 12V or greater.
MAX680/MAX681
+5V to ±10V Voltage Converters
_______________________________________________________________________________________ 5
MAX680
C1
22µF
C3
22µF
V+ OUT
V- OUT
VCC IN
GND
C4
22µF
C2
22µF
C1- 8
7
6
5
C2+
V-
V+
1
2
3
4
C1+
VCC
GND
C2-
Figure 3. Positive and Negative Converter
MAX680/MAX681
The MAX680/MAX681 are not voltage regulators: the
output source resistance of either charge pump is
approximately 150Ωat room temperature with VCC at
5V. Under light load with an input VCC of 5V, V+ will
approach +10V and V- will be at -10V. However both,
V+ and V- will droop toward GND as the current drawn
from either V+ or V- increases, since the negative con-
verter draws its power from the positive converter’s out-
put. To predict output voltages, treat the chips as two
separate converters and analyze them separately. First,
the droop of the negative supply (VDROP-) equals the
current drawn from V- - (IL-) times the source resistance
of the negative converter (RS-):
VDROP -= I
L
- x RS-
Likewise, the positive supply droop (VDROP+) equals
the current drawn from the positive supply (IL+) times
the positive converter’s source resistance (RS+),
except that the current drawn from the positive supply
is the sum of the current drawn by the load on the posi-
tive supply (IL+) plus the current drawn by the negative
converter (IL-):
(VDROP+) = IL+ x RS+ = (IL+ + IL-) x RS+
The positive output voltage will be:
V+ = 2VCC – VDROP+
The negative output voltage will be:
V- = (V+ - VDROP) = - (2VCC - VDROP + - VDROP-)
The positive and negative charge pumps are tested
and specified separately to provide the separate values
of output source resistance for use in the above formu-
las. When the positive charge pump is tested, the neg-
ative charge pump is unloaded. When the negative
charge pump is tested, the positive supply V+ is from
an external source, isolating the negative charge
pump.
Calculate the ripple voltage on either output by noting
that the current drawn from the output is supplied by
the reservoir capacitor alone during one half-cycle of
the clock. This results in a ripple of:
VRIPPLE = 1⁄2IOUT (1⁄ fPUMP)(1⁄ CR)
For the nominal fPUMP of 8kHz with 10µF reservoir
capacitors, the ripple will be 30mV with IOUT at 5mA.
Remember that in most applications, the positive
charge pump’s IOUT is the load current plus the current
taken by the negative charge pump.
+5V to ±10V Voltage Converters
6 _______________________________________________________________________________________
MAX680
22µF
22µF
C1- 8
7
6
5
C2+
V-
V+
1
2
3
4
C1+
VCC
GND
C2-
MAX680
22µF
22µF
22µF
V+ OUT
V- OUT
VCC IN
GND
22µF
C1- 8
7
6
5
C2+
V-
V+
1
2
3
4
C1+
VCC
GND
C2-
Figure 4. Paralleling MAX680s For Lower Source Resistance
Paralleling Devices
Paralleling multiple MAX680/MAX681s reduces the out-
put resistance of both the positive and negative con-
verters. The effective output resistance is the output
resistance of a single device divided by the number of
devices. As Figure 4 shows, each MAX680 requires
separate pump capacitors C1 and C2, but all can
share a single set of reservoir capacitors.
±5V Regulated Supplies from
a Single 3V Battery
Figure 5 shows a complete ±5V power supply using one
3V battery. The MAX680/MAX681 provide +6V at V+,
which is regulated to +5V by the MAX666, and -6V,
which is regulated to -5V by the MAX664. The MAX666
and MAX664 are pretrimmed at wafer sort and require
no external setting resistors, minimizing part count. The
combined quiescent current of the MAX680/MAX681,
MAX663, and MAX664 is less than 500µA, while the out-
put current capability is 5mA. The MAX680/MAX681
input can vary from 3V to 6V without affecting regulation
appreciably. With higher input voltage, more current can
be drawn from the MAX680/MAX681 outputs. With 5V at
VCC, 10mA can be drawn from both regulated outputs
simultaneously. Assuming 150Ωsource resistance for
both converters, with (IL++ IL-) = 20mA, the positive
charge pump will droop 3V, providing +7V for the nega-
tive charge pump. The negative charge pump will droop
another 1.5V due to its 10mA load, leaving -5.5V at V-
sufficient to maintain regulation for the MAX664 at this
current.
MAX680/MAX681
+5V to ±10V Voltage Converters
_______________________________________________________________________________________ 7
MAX680
100µF10µF
0.1µF
100µF
100µF
+12V TO +6V
-12V TO -6V
0.1µF
10µF
100µF
C1+
GND
VCC
C1-
C2-
V+
LBI
LOW-BATTERY
WARNING AT 3.5V
SENSE
VOUTVIN
6V TO 3V
2MΩ
1.2MΩ+5V
-5V
GND
LBO
SDNGND VSET
V-
C2+
MAX666
VIN VOUT1
VOUT2
SENSE
SDNGND VSET
MAX664
Figure 5. Regulated +5V and -5V from a Single Battery
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1989 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX680/MAX681
+5V to ±10V Voltage Converters
________________________________________________________Package Information
___________________Chip Topography
DIM
A
A1
B
C
E
e
H
L
MIN
0.053
0.004
0.014
0.007
0.150
0.228
0.016
MAX
0.069
0.010
0.019
0.010
0.157
0.244
0.050
MIN
1.35
0.10
0.35
0.19
3.80
5.80
0.40
MAX
1.75
0.25
0.49
0.25
4.00
6.20
1.27
INCHES MILLIMETERS
21-0041A
Narrow SO
SMALL-OUTLINE
PACKAGE
(0.150 in.)
DIM
D
D
D
MIN
0.189
0.337
0.386
MAX
0.197
0.344
0.394
MIN
4.80
8.55
9.80
MAX
5.00
8.75
10.00
INCHES MILLIMETERS
PINS
8
14
16
1.270.050
L
0°-8°
HE
D
e
A
A1 C
0.101mm
0.004in.
B
VCC
C1+
0.72"
(1.83mm)
0.116"
(2.95mm)
C2+
C2-
V- GND
C1- V+
