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PDF MAX865EUA Data sheet ( Hoja de datos )
| Número de pieza | MAX865EUA | |
| Descripción | Compact / Dual-Output Charge Pump | |
| Fabricantes | Maxim Integrated | |
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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 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.
________________________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.
1 page  
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 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- 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
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