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 75Ω
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.
____________________________Features
o
1.11mm-High µMAX Package
o
Compact: Circuit Fits in 0.08in
2
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)
MAX865
______________Ordering Information
PART
MAX865C/D
MAX865EUA
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice
8 µMAX
________________________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
__________Typical Operating Circuit
V
IN
(+1.5V to +6.0V)
__________________Pin Configuration
IN
C1+
MAX865
V+
+2*V
IN
TOP VIEW
C1-
C2+
C1-
C2+
C2-
1
2
3
8
C1+
V+
IN
GND
MAX865
7
6
5
V-
C2-
GND
-2*V
IN
V-
4
µMAX
GND
GND
+V
IN
to ±2V
IN
CONVERTER
________________________________________________________________
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.
Compact, Dual-Output Charge Pump
MAX865
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 (T
A
= +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
(V
IN
= 5V, C1 = C2 = C3 = C4 = 3.3µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Minimum Supply Voltage
Maximum Supply Voltage
Supply Current
Oscillator Frequency
R
LOAD
= 10kΩ
R
LOAD
= 10kΩ
T
A
= +25°C
T
A
= -40°C to +85°C (Note 1)
T
A
= +25°C
T
A
= -40°C to +85°C (Note 1)
I
V+
= 1mA,
I
V-
= 0mA
V+ = 10V (forced),
I
V-
= 1mA
Power Efficiency
Voltage Conversion Efficiency
I
L
= 5mA
V+, R
L
=
∞
V-, R
L
=
∞
95
90
T
A
= +25°C
T
A
= T
MIN
to T
MAX
T
A
= +25°C
T
A
= T
MIN
to T
MAX
85
99
98
75
19.5
18
150
24
0.6
CONDITIONS
MIN
2.0
TYP
1.5
6.0
1.05
1.15
32.5
34
200
280
100
140
%
%
Ω
MAX
UNITS
V
V
mA
kHz
Output Resistance
Note 1:
These specifications are guaranteed by design and are not production tested.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, V
IN
= 5V, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
(V
IN
= 5V)
MAX865-01
EFFICIENCY vs. OUTPUT CURRENT
(V
IN
= 3.3V)
MAX865-02
EFFICIENCY vs. OUTPUT CURRENT
(V
IN
= 2V)
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V-
V+
MAX865-03
100
90
80
EFFICIENCY (%)
V-
V+
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V-
V+
100
70
60
50
40
30
20
10
0
0
2
4
6
8
10 12
14 16 18
0
1
2
3
4
5
6
7
8
0
0.5
1.0
1.5
2.0
2.5
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
2
_______________________________________________________________________________________
Compact, Dual-Output Charge Pump
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= 5V, T
A
= +25°C, unless otherwise noted.)
OUTPUT VOLTAGE vs.
OUTPUT CURRENT
MAX865-04
MAX865
OUTPUT VOLTAGE RIPPLE
vs. PUMP CAPACITANCE
MAX865-05
OUTPUT CURRENT
vs. PUMP CAPACITANCE
OUTPUT CURRENT, V+ TO V- (mA)
V
IN
= 4.75V, V+ +
|
V-
|
= 16V
MAX865-06
10
8
OUTPUT VOLTAGE, V+, V- (V)
6
4
2
0
-2
-4
-6
-8
-10
0
2
4
6
8
10
OUTPUT CURRENT (mA)
V+
12
BOTH V+ AND
V- LOADED EQUALLY
C1 = C2 = C3 = C4 = 3.3µF
V
IN
= 4.75V
V+
400
OUTPUT VOLTAGE RIPPLE (mVp-p)
350
300
250
200
150
100
50
0
0
5
F
D
C1 = C2 = C3 = C4
A: V+, IN = 4.75V, V+ +
|
V-
|
= 16V
B: V+, IN = 3.15V, V+ +
|
V-
|
= 10V
C: V+, IN = 1.90V, V+ +
|
V-
|
= 6V
D: V-, IN = 4.75V, V+ +
|
V-
|
= 16V
E: V-, IN = 3.15V, V+ +
|
V-
|
= 10V
F: V-, IN = 1.90V, V+ +
|
V-
|
= 6V
AE
BC
7
6
5
4
3
V-
V
IN
= 3.15V, V+ +
|
V-
|
= 10V
V
IN
= 1.90V, V+ +
|
V-
|
= 6V
2
1
C1 = C2 = C3 = C4
0
V-
14
10 15 20 25 30 35 40 45 50
PUMP CAPACITANCE (µF)
0
5
10 15 20 25 30 35 40 45 50
PUMP CAPACITANCE (µF)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX865-07
OUTPUT RESISTANCE
vs. TEMPERATURE
C1 = C2 = C3 = C4 = 3.3µF
V-, V
IN
= 3.3V
V-, V
IN
= 5.0V
MAX865-08
1000
900
SUPPLY CURRENT (µA)
800
700
600
500
400
300
200
100
0
2.0 2.5 3.0
3.5 4.0 4.5
C1 = C2 = C3 = C4 = 3.3µF
300
250
200
150
100
50
0
V+, V
IN
= 5.0V
OUTPUT RESISTANCE (Ω)
V+, V
IN
= 3.3V
5.0 5.5 6.0
-55 -35 -15
5
25
45
65
85 105 125
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
PUMP FREQUENCY
vs. TEMPERATURE
MAX865-09
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
MAX865-10
27
V
IN
= 5.0V
25
PUMP FREQUENCY (kHz)
23
21
V
IN
= 2.0V
19
17
15
-40
-20
0
20
40
60
80
C1 = C2 = C3 = C4 = 3.3µF
V
IN
= 3.3V
250
OUTPUT RESISTANCE (Ω)
200
V-
150
V+
100
50
C1 = C2 = C3 = C4 = 3.3µF
0
100
2.0 2.5
3.0
3.5
4.0 4.5
5.0
5.5 6.0
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
Compact, Dual-Output Charge Pump
MAX865
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= 5V, T
A
= +25°C, unless otherwise noted.)
OUTPUT RIPPLE
(C1 = C2 = C3 = C4 = 1µF)
OUTPUT RIPPLE
(C1 = C2 = C3 = C4 = 3.3µF)
V- OUTPUT
20mV/div
V- OUTPUT
10mV/div
V+ OUTPUT
50mV/div
V+ OUTPUT
10mV/div
10µs/div
V
IN
= 4.75V, 1mA LOAD
V
IN
= 4.75V, 1mA LOAD
10µs/div
_____________________Pin Description
PIN
NAME
C1-
C2+
C2-
V-
GND
IN
V+
C1+
FUNCTION
Negative Terminal of the Flying Boost
Capacitor
Positive Terminal of the Flying
Inverting Capacitor
Negative Terminal of the Flying
Inverting Capacitor
Output of the Inverting Charge Pump
Ground
Positive Power-Supply Input
3.3µF
3.3µF
C2-
V-
IN
GND
V
IN
1
2
3
4
5
6
7
8
3.3µF
C1-
C2+
MAX865
C1+
I
V
+
V+
3.3µF
R
L
+
OUT+
I
V
-
R
L
-
Output of the Boost Charge Pump
Positive Terminal of the Flying Boost
Capacitor
OUT-
Figure 1. Test Circuit
4
_______________________________________________________________________________________
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 (V
IN
).
During the second half cycle, switches S1 and S3
open, switches S2 and S4 close, and capacitor C1 is
level shifted upward by V
IN
. Assuming ideal switches
and no load on C3, charge transfers into C3 from C1
such that the voltage on C3 will be 2V
IN
, 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 2V
IN
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.
MAX865
Charge-Pump Output
The MAX865 is not a voltage regulator: the output
source resistance of either charge pump is approxi-
mately 150Ω at room temperature with V
IN
= +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
(V
DROOP-
) is the product of the current draw from V-
(I
V-
) and the source resistance of the negative convert-
er (RS-):
V
DROOP-
= I
V -
x RS -
The droop of the positive supply (V
DROOP+
) is the
product of the current draw from the positive supply
(I
LOAD+
) and the source resistance of the positive
a)
V+
S1
IN
C1
C3
C1+
S2
b)
V+
S5
C2+
S6
GND
I
V
+
R
L
+
C2
I
V
-
C4
S3
GND
C1-
S4
I
N
GND
C2-
S7
S8
V-
R
L
-
Figure 2. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump
_______________________________________________________________________________________
5
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