MAX865 Compact, Dual-Output Charge Pump
19-0472; Rev 1; 7/97
Compact, Dual-Output Charge Pump
____________________________Features
♦ 1.11mm-High µMAX Package
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 standard 8-pin SOIC. For a device with selectable frequencies and logic-controlled shutdown, refer to the MAX864
data sheet.
♦ +1.5V to +6.0V Input Voltage
________________________Applications
Low-Voltage GaAsFET Bias in Wireless Handsets
♦ Compact: Circuit Fits in 0.08in2
♦ Requires Only Four Capacitors
♦ Dual Outputs (positive and negative)
♦ 20kHz (min) Frequency (above the audio range)
______________Ordering Information
PART
TEMP. RANGE
MAX865C/D
MAX865EUA
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice
8 µMAX
VCO and GaAsFET Supplies
Split Supply from 3 Ni Cells or 1 Li+ Cell
Low-Cost Split Supply for Low-Voltage
Data-Acquisition Systems
__________Typical Operating Circuit
Split Supply for Analog Circuitry
LCD Panels
VIN
(+1.5V to +6.0V)
__________________Pin Configuration
IN
C1+
MAX865
TOP VIEW
V+
+2*VIN
V-
-2*VIN
C1-
C1-
1
8
C1+
C2+
2
7
V+
C2-
3
6
IN
5
GND
MAX865
V- 4
C2+
C2GND
µMAX
GND
GND
+VIN to ±2VIN 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.
MAX865
_______________General Description
The MAX865 is a CMOS charge-pump DC-DC converter 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 voltage. The input voltage ranges from +1.5V to +6.0V.
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
CONDITIONS
Minimum Supply Voltage
RLOAD = 10kΩ
Maximum Supply Voltage
RLOAD = 10kΩ
MIN
TYP
2.0
1.5
0.6
TA = -40°C to +85°C (Note 1)
19.5
TA = -40°C to +85°C (Note 1)
Output Resistance
Power Efficiency
24
V
V
1.05
mA
32.5
18
IV+ = 1mA,
IV- = 0mA
TA = +25°C
V+ = 10V (forced),
IV- = 1mA
TA = +25°C
kHz
34
150
TA = TMIN to TMAX
200
280
75
Ω
100
TA = TMIN to TMAX
140
IL = 5mA
Voltage Conversion Efficiency
UNITS
1.15
TA = +25°C
Oscillator Frequency
MAX
6.0
TA = +25°C
Supply Current
85
V+, RL = ∞
95
99
V-, RL = ∞
90
98
%
%
Note 1: These specifications are guaranteed by design and are not production tested.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, VIN = 5V, TA = +25°C, unless otherwise noted.)
80
EFFICIENCY (%)
V-
70
60
50
40
100
70
60
50
40
70
60
50
40
30
30
20
20
20
10
10
10
0
0
2
4
6
8
10 12
14 16 18
OUTPUT CURRENT (mA)
V-
80
V-
30
0
V+
90
EFFICIENCY (%)
80
2
V+
90
MAX865-03
100
MAX865-02
V+
90
MAX865-01
100
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 2V)
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 3.3V)
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 5V)
EFFICIENCY (%)
MAX865
Compact, Dual-Output Charge Pump
0
0
1
2
3
4
5
6
OUTPUT CURRENT (mA)
7
8
0
0.5
1.0
1.5
2.0
OUTPUT CURRENT (mA)
_______________________________________________________________________________________
2.5
Compact, Dual-Output Charge Pump
(Circuit of Figure 1, VIN = 5V, TA = +25°C, unless otherwise noted.)
OUTPUT VOLTAGE RIPPLE
vs. PUMP CAPACITANCE
VBOTH V+ AND
V- LOADED EQUALLY
0
-2
C1 = C2 = C3 = C4 = 3.3µF
VIN = 4.75V
-4
V-
-6
-8
2
4
6
8
10
250
200
F
150
D
100
MAX865-05
AE
BC
50
VIN = 3.15V, V+ + |V-| = 10V
4
3
VIN = 1.90V, V+ + |V-| = 6V
2
1
14
12
0
5
0
10 15 20 25 30 35 40 45 50
5
0
10 15 20 25 30 35 40 45 50
PUMP CAPACITANCE (µF)
PUMP CAPACITANCE (µF)
OUTPUT RESISTANCE
vs. TEMPERATURE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
300
MAX865-07
1000
C1 = C2 = C3 = C4 = 3.3µF
900
5
0
OUTPUT CURRENT (mA)
800
OUTPUT RESISTANCE (Ω)
SUPPLY CURRENT (µA)
700
600
500
400
300
200
250
200
C1 = C2 = C3 = C4 = 3.3µF
V-, VIN = 3.3V
V-, VIN = 5.0V
150
100
V+, VIN = 3.3V
V+, VIN = 5.0V
50
100
0
0
2.0 2.5
3.0
3.5
4.0 4.5
25
5
45
85 105 125
65
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
PUMP FREQUENCY
vs. TEMPERATURE
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
27
VIN = 5.0V
VIN = 3.3V
23
250
OUTPUT RESISTANCE (Ω)
25
21
VIN = 2.0V
19
17
-55 -35 -15
5.0 5.5 6.0
MAX865-09
0
300
VIN = 4.75V, V+ + |V-| = 16V
6
C1 = C2 = C3 = C4
V+
-10
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
200
15
V-
150
V+
100
50
C1 = C2 = C3 = C4 = 3.3µF
MAX865-10
2
7
MAX865-08
4
C1 = C2 = C3 = C4
350
OUTPUT CURRENT, V+ TO V- (mA)
6
PUMP FREQUENCY (kHz)
OUTPUT VOLTAGE, V+, V- (V)
400
MAX865-04
V+
8
OUTPUT VOLTAGE RIPPLE (mVp-p)
10
OUTPUT CURRENT
vs. PUMP CAPACITANCE
MAX865-06
OUTPUT VOLTAGE vs.
OUTPUT CURRENT
C1 = C2 = C3 = C4 = 3.3µF
0
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
2.0 2.5
3.0
3.5
4.0 4.5
5.0
5.5 6.0
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
MAX865
____________________________Typical Operating Characteristics (continued)
MAX865
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)
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
10µs/div
VIN = 4.75V, 1mA LOAD
VIN = 4.75V, 1mA LOAD
_____________________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-
5
GND
6
IN
Positive Power-Supply Input
7
V+
Output of the Boost Charge Pump
8
C1+
Output of the Inverting Charge Pump
Ground
VIN
3.3µF
C1-
C1+
IV+
C2+ MAX865
V+
C2-
IN
3.3µF
3.3µF
V-
RL+
GND
IV3.3µF
Positive Terminal of the Flying Boost
Capacitor
RL-
OUT-
Figure 1. Test Circuit
4
OUT+
_______________________________________________________________________________________
Compact, Dual-Output Charge Pump
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-channel devices.
The MAX865 contains all the circuitry needed to implement a voltage doubler/inverter. Only four external
capacitors are needed. These may be polarized electrolytic or ceramic capacitors with values ranging from
1µF to 100µF.
Figure 2a shows the ideal operation of the positive voltage 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 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+).
Charge-Pump Output
The MAX865 is not a voltage regulator: the output
source resistance of either charge pump is approximately 150Ω at 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- increases, since V- is derived from V+. Treating each converter 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 converter (RS-):
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
a)
VDROOP- = 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
b)
V+
S1
C1+
V+
S2
S5
C2+
S6
GND
IN
C3
C1
IV+
RL+
C2
IV-
RL-
C4
S3
S4
S7
IN
GND
C1-
S8
V-
GND
C2-
Figure 2. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump
_______________________________________________________________________________________
5
MAX865
_______________Detailed Description
MAX865
Compact, Dual-Output Charge Pump
converter (RS+), where ILOAD+ is the combination of IVand the external load on V+ (IV+):
(
)
VDROOP+ = ILOAD+ x RS+ = I V+ + I V - x RS+
Determine V+ and V- as follows:
V+ = 2VIN - VDROOP+
V - = (V+ - VDROOP ) = -(2VIN - VDROOP+ - VDROOP- )
The output resistance for the positive and negative
charge pumps are tested and specified separately. The
positive charge pump is tested with V- unloaded. The
negative charge pump is tested with V+ supplied from
an external source, isolating the negative charge
pump.
Current draw from either V+ or V- is supplied by the
reservoir capacitor alone during one half cycle of the
clock. Calculate the resulting ripple voltage on either
output as follows:
VRIPPLE =
1
2
ILOAD (1 / fPUMP ) (1 / CRESERVOIR )
where ILOAD is the load on either V+ or V-. For the typical fPUMP of 30kHz with 3.3µF reservoir capacitors, the
ripple is 25mV when ILOAD is 5mA. Remember that, in
most applications, the total load on V+ is the V+ load
current (I V+) and the current taken by the negative
charge pump (IV-).
Efficiency Considerations
Theoretically, a charge-pump voltage multiplier can
approach 100% power efficiency under the following
conditions:
• The charge-pump switches have virtually no offset
and extremely low on-resistance.
• The drive circuitry consumes minimal power.
• The impedances of the reservoir and pump capacitors are negligible.
For the MAX865, the energy loss per clock cycle is the
sum of the energy loss in the positive and negative
converters, as follows:
LOSSCYCLE = LOSSPOS + LOSSNEG
=
+
1
2
1
2
2
C1 ( V + ) − 2( V + ) ( VIN )


2
2
C2 ( V + ) − ( V − ) 


The average power loss is simply:
PLOSS = LOSSCYCLE x fPUMP
Resulting in an efficiency of:
(
η = Total Output Power / Total Output Power − PLOSS
VIN
3.3µF
3.3µF
1
2
3.3µF
C1C2- MAX865
C1+
V+
8
1
C1-
7
2
C2+ MAX865
V+
C2-
IN
3.3µF
3
4
C2V-
IN
GND
6
3
5
4
V-
C1+
GND
8
7
OUT+
3.3µF
6
IN
5
GND
3.3µF
OUT-
Figure 3. Paralleling MAX865s
6
_______________________________________________________________________________________
)
Compact, Dual-Output Charge Pump
Charge-Pump Capacitor Selection
To maintain the lowest output resistance, use capacitors
with low effective series resistance (ESR). The chargepump output resistance is a function of C1, C2, C3, and
C4’s ESR. Therefore, minimizing the charge-pump
capacitors’ ESR minimizes the total output resistance.
__________Applications Information
Paralleling Devices
Paralleling multiple MAX865s (Figure 3) reduces the
output resistance of both the positive and negative converters. The effective output resistance is the output
resistance of one device divided by the number of
devices. Separate C1 and C2 charge-pump capacitors
are required for each MAX865, but the reservoir capacitors C3 and C4 can be shared.
Heavy Output Current Loads
When under heavy loads, where V+ is sourcing current
into V- (i.e., load current flows from V+ to V-, rather than
from supply to ground), do not allow the V- supply to
pull above ground. In applications where large currents
flow from V+ to V-, use a Schottky diode (1N5817)
between GND and V-, with the anode connected to
GND (Figure 4).
Positive and Negative Converter
Layout and Grounding
The MAX865 is most commonly used as a dual chargepump voltage converter that provides positive and negative outputs of two times a positive input voltage. The
Typical Operating Circuit shows that only four external
components are needed: capacitors C1 and C3 for the
positive pump, C2 and C4 for the negative pump. In
most applications, all four capacitors are low-cost,
3.3µF polarized electrolytics. For applications where PC
board space is at a premium and very low currents are
being drawn from the MAX865, 1µF capacitors may be
used for the pump capacitors C1 and C2, with 1µF
reservoir capacitors C3 and C4. Capacitors C2 and C4
must be rated at 12V or greater.
Good layout is important, primarily for good noise performance. To ensure good layout:
• Mount all components as close together as possible
• Keep traces short to minimize parasitic inductance
and capacitance
• Use a ground plane.
GND
MAX865
V-
Figure 4. A Schottky diode protects the MAX865 when large
currents flow from V+ to V-.
_______________________________________________________________________________________
7
MAX865
A substantial voltage difference exists between (V+ VIN) and VIN for the positive pump, and between V+
and V- if the impedances of the pump capacitors
(C1 and C2) are large with respect to their output
loads.
Larger values of reservoir capacitors (C3 and C4)
reduce output ripple. Larger values of both pump and
reservoir capacitors improve power efficiency.
Compact, Dual-Output Charge Pump
MAX865
___________________Chip Topography
TRANSISTOR COUNT: 80
SUBSTRATE CONNECTED TO V+
C1-
C1+
C2+
V+
0.084"
(2.13mm)
IN
C2-
V-
GND
0.058"
(1.47mm)
________________________________________________________Package Information
DIM
C
α
A
0.101mm
0.004 in
e
B
A1
L
A
A1
B
C
D
E
e
H
L
α
INCHES
MAX
MIN
0.044
0.036
0.008
0.004
0.014
0.010
0.007
0.005
0.120
0.116
0.120
0.116
0.0256
0.198
0.188
0.026
0.016
6°
0°
MILLIMETERS
MIN
MAX
0.91
1.11
0.10
0.20
0.25
0.36
0.13
0.18
2.95
3.05
2.95
3.05
0.65
4.78
5.03
0.41
0.66
0°
6°
21-0036D
E
H
8-PIN µMAX
MICROMAX SMALL-OUTLINE
PACKAGE
D
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
© 1997 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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