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19-0472; Rev 1; 7/97
Compact, Dual-Output Charge Pump
_______________General Description
The MAX865 is a CMOS charge-pump DC-DC convert-
er in an ultra-small µMAX package. It produces positive
and negative outputs from a single positive input, and
requires only four capacitors. The charge pump first
doubles the input voltage, then inverts the doubled volt-
age. The input voltage ranges from +1.5V to +6.0V.
The internal oscillator is guaranteed to be between
20kHz and 38kHz, keeping noise above the audio
range while consuming minimal supply current. A 75
output impedance permits useful output currents up to
20mA.
The MAX865 comes in a 1.11mm-high, 8-pin µMAX
package that occupies half the board area of a stan-
dard 8-pin SOIC. For a device with selectable frequen-
cies and logic-controlled shutdown, refer to the MAX864
data sheet.
________________________Applications
Low-Voltage GaAsFET Bias in Wireless Handsets
VCO and GaAsFET Supplies
Split Supply from 3 Ni Cells or 1 Li+ Cell
Low-Cost Split Supply for Low-Voltage
Data-Acquisition Systems
Split Supply for Analog Circuitry
LCD Panels
__________________Pin Configuration
TOP VIEW
C1- 1
C2+ 2
C2- 3
V- 4
MAX865
µMAX
8 C1+
7 V+
6 IN
5 GND
____________________________Features
o 1.11mm-High µMAX Package
o Compact: Circuit Fits in 0.08in2
o Requires Only Four Capacitors
o Dual Outputs (positive and negative)
o +1.5V to +6.0V Input Voltage
o 20kHz (min) Frequency (above the audio range)
______________Ordering Information
PART
MAX865C/D
MAX865EUA
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice
8 µMAX
__________Typical Operating Circuit
VIN
(+1.5V to +6.0V)
IN
C1+ MAX865
C1-
V+
C2+
C2-
GND
V-
+2*VIN
-2*VIN
GND
+VIN to ±2VIN CONVERTER
GND
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.

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Compact, Dual-Output Charge Pump
ABSOLUTE MAXIMUM RATINGS
V+ to GND .................................................................+12V, -0.3V
IN to GND .................................................................+6.2V, -0.3V
V- to GND ..................................................................-12V, +0.3V
V- Output Current .............................................................100mA
V- Short-Circuit to GND ................................................Indefinite
Continuous Power Dissipation (TA = +70°C)
µMAX (derate 4.1mW/°C above +70°C) .......................330mW
Operating Temperature Range
MAX865EUA .....................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
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.
ELECTRICAL CHARACTERISTICS
(VIN = 5V, C1 = C2 = C3 = C4 = 3.3µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
Minimum Supply Voltage
Maximum Supply Voltage
Supply Current
Oscillator Frequency
Output Resistance
Power Efficiency
Voltage Conversion Efficiency
CONDITIONS
RLOAD = 10k
RLOAD = 10k
TA = +25°C
TA = -40°C to +85°C (Note 1)
TA = +25°C
TA = -40°C to +85°C (Note 1)
IV+ = 1mA,
IV- = 0mA
TA = +25°C
TA = TMIN to TMAX
V+ = 10V (forced),
IV- = 1mA
TA = +25°C
TA = TMIN to TMAX
IL = 5mA
V+, RL =
V-, RL =
MIN TYP MAX
2.0 1.5
6.0
0.6 1.05
1.15
19.5 24 32.5
18 34
150 200
280
75 100
140
85
95 99
90 98
Note 1: These specifications are guaranteed by design and are not production tested.
UNITS
V
V
mA
kHz
%
%
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, VIN = 5V, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 5V)
100
90 V+
80
70 V-
60
50
40
30
20
10
0
0 2 4 6 8 10 12 14 16 18
OUTPUT CURRENT (mA)
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 3.3V)
100
90 V+
80 V-
70
60
50
40
30
20
10
0
012 345 678
OUTPUT CURRENT (mA)
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 2V)
100
V+
90
80 V-
70
60
50
40
30
20
10
0
0
0.5 1.0 1.5 2.0
OUTPUT CURRENT (mA)
2.5
2 _______________________________________________________________________________________

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Compact, Dual-Output Charge Pump
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 5V, TA = +25°C, unless otherwise noted.)
OUTPUT VOLTAGE vs.
OUTPUT CURRENT
10 V+
8
6
4 V-
2 BOTH V+ AND
0 V- LOADED EQUALLY
-2 C1 = C2 = C3 = C4 = 3.3µF
-4 VIN = 4.75V
-6
V-
-8
-10
0
V+
2 4 6 8 10 12
OUTPUT CURRENT (mA)
14
OUTPUT VOLTAGE RIPPLE
vs. PUMP CAPACITANCE
400
C1 = C2 = C3 = C4
350
A: V+, IN = 4.75V, V+ + |V-| = 16V
300 B: V+, IN = 3.15V, V+ + |V-| = 10V
C: V+, IN = 1.90V, V+ + |V-| = 6V
250 D: V-, IN = 4.75V, V+ + |V-| = 16V
200
E: V-, IN = 3.15V, V+ + |V-| = 10V
F: V-, IN = 1.90V, V+ + |V-| = 6V
150 F
100 D A E
BC
50
0
0 5 10 15 20 25 30 35 40 45 50
PUMP CAPACITANCE (µF)
OUTPUT CURRENT
vs. PUMP CAPACITANCE
7
VIN = 4.75V, V+ + |V-| = 16V
6
5 VIN = 3.15V, V+ + |V-| = 10V
4
3
VIN = 1.90V, V+ + |V-| = 6V
2
1
C1 = C2 = C3 = C4
0
0 5 10 15 20 25 30 35 40 45 50
PUMP CAPACITANCE (µF)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
1000
900 C1 = C2 = C3 = C4 = 3.3µF
800
700
600
500
400
300
200
100
0
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
OUTPUT RESISTANCE
vs. TEMPERATURE
300
C1 = C2 = C3 = C4 = 3.3µF
250 V-, VIN = 3.3V
200 V-, VIN = 5.0V
150
100 V+, VIN = 3.3V
50 V+, VIN = 5.0V
0
-55 -35 -15 5 25 45 65 85 105 125
TEMPERATURE (°C)
PUMP FREQUENCY
vs. TEMPERATURE
27
VIN = 5.0V
25
23 VIN = 3.3V
21
VIN = 2.0V
19
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
250
200 V-
150
V+
100
17 C1 = C2 = C3 = C4 = 3.3µF
50
C1 = C2 = C3 = C4 = 3.3µF
15
-40 -20
0 20 40 60
TEMPERATURE (°C)
80 100
0
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________ 3

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Compact, Dual-Output Charge Pump
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 5V, TA = +25°C, unless otherwise noted.)
OUTPUT RIPPLE
(C1 = C2 = C3 = C4 = 1µF)
V- OUTPUT
20mV/div
10µs/div
VIN = 4.75V, 1mA LOAD
V+ OUTPUT
50mV/div
OUTPUT RIPPLE
(C1 = C2 = C3 = C4 = 3.3µF)
V- OUTPUT
10mV/div
10µs/div
VIN = 4.75V, 1mA LOAD
V+ OUTPUT
10mV/div
_____________________Pin Description
PIN NAME
FUNCTION
1
C1-
Negative Terminal of the Flying Boost
Capacitor
2
C2+
Positive Terminal of the Flying
Inverting Capacitor
3
C2-
Negative Terminal of the Flying
Inverting Capacitor
4 V- Output of the Inverting Charge Pump
5 GND Ground
6 IN Positive Power-Supply Input
7 V+ Output of the Boost Charge Pump
8
C1+
Positive Terminal of the Flying Boost
Capacitor
VIN
3.3µF
C1-
C1+
3.3µF
C2+ MAX865
C2-
V+
IN
V- GND
Figure 1. Test Circuit
OUT+
IV+
3.3µF
RL+
IV-
3.3µF
RL-
OUT-
4 _______________________________________________________________________________________

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Compact, Dual-Output Charge Pump
_______________Detailed Description
The MAX865 contains all the circuitry needed to imple-
ment a voltage doubler/inverter. Only four external
capacitors are needed. These may be polarized elec-
trolytic or ceramic capacitors with values ranging from
1µF to 100µF.
Figure 2a shows the ideal operation of the positive volt-
age doubler. The on-chip oscillator generates a 50%
duty-cycle clock signal. During the first half cycle,
switches S2 and S4 open, switches S1 and S3 close,
and capacitor C1 charges to the input voltage (VIN).
During the second half cycle, switches S1 and S3
open, switches S2 and S4 close, and capacitor C1 is
level shifted upward by VIN. Assuming ideal switches
and no load on C3, charge transfers into C3 from C1
such that the voltage on C3 will be 2VIN, generating the
positive supply output (V+).
Figure 2b illustrates the ideal operation of the negative
converter. The switches of the negative converter are
out of phase with the positive converter. During the
second half cycle, switches S6 and S8 open and
switches S5 and S7 close, charging C2 from V+
(pumped up to 2VIN by the positive charge pump) to
GND. In the first half of the clock cycle, switches S5
and S7 open, switches S6 and S8 close, and the
charge on capacitor C2 transfers to C4, generating the
negative supply. The eight switches are CMOS power
MOSFETs. Switches S1, S2, S4, and S5 are P-channel
devices, while switches S3, S6, S7, and S8 are N-chan-
nel devices.
Charge-Pump Output
The MAX865 is not a voltage regulator: the output
source resistance of either charge pump is approxi-
mately 150at room temperature with VIN = +5V, and
V+ and V- will approach +10V and -10V, respectively,
when lightly loaded. Both V+ and V- will droop toward
GND as the current draw from either V+ or V- increas-
es, since V- is derived from V+. Treating each convert-
er separately, the droop of the negative supply
(VDROOP-) is the product of the current draw from V-
(IV-) and the source resistance of the negative convert-
er (RS-):
VDROOP- = IV- x RS -
The droop of the positive supply (VDROOP+) is the
product of the current draw from the positive supply
(ILOAD+) and the source resistance of the positive
a)
IN
GND
S1 C1+ S2
C1 C3
S3 S4
C1-
b)
V+ V+
S5
IV+ RL+
IN GND
S7
C2+ S6
C2
C4
S8
C2-
IV-
GND
RL-
V-
Figure 2. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump
_______________________________________________________________________________________ 5