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PDF MAX829 Data sheet ( Hoja de datos )
| Número de pieza | MAX829 | |
| Descripción | Switched-Capacitor Voltage Inverters | |
| Fabricantes | Maxim Integrated | |
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19-0495; Rev 3; 9/99
Switched-Capacitor Voltage Inverters
General Description
The ultra-small MAX828/MAX829 monolithic, CMOS
charge-pump inverters accept input voltages ranging
from +1.5V to +5.5V. The MAX828 operates at 12kHz,
and the MAX829 operates at 35kHz. Their high efficiency
(greater than 90% over most of the load-current range)
and low operating current (60µA for the MAX828) make
these devices ideal for both battery-powered and board-
level voltage-conversion applications.
The MAX828/MAX829 combine low quiescent current
and high efficiency. Oscillator control circuitry and four
power MOSFET switches are included on-chip.
Applications include generating a -5V supply from a +5V
logic supply to power analog circuitry. Both parts come
in a 5-pin SOT23-5 package and can deliver 25mA with
a voltage drop of 500mV.
For a similar device with logic-controlled shutdown,
refer to the MAX1719/MAX1720/MAX1721. For applica-
tions requiring more power, the MAX860 delivers up to
50mA with a voltage drop of 600mV, in a space-saving
µMAX package.
Applications
Small LCD Panels
Cell Phones
Medical Instruments
Handy-Terminals, PDAs
Battery-Operated Equipment
Features
o 5-Pin SOT23-5 Package
o 95% Voltage Conversion Efficiency
o Inverts Input Supply Voltage
o 60µA Quiescent Current (MAX828)
o +1.5V to +5.5V Input Voltage Range
o Requires Only Two Capacitors
o 25mA Output Current
Ordering Information
PART
MAX828EUK
MAX829EUK
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
5 SOT23-5
5 SOT23-5
SOT
TOP MARK
AABI
AABJ
Typical Operating Circuit
Pin Configuration
5
C1+
2
IN
3
C1-
4
GND
MAX828
MAX829
OUT 1
INPUT
SUPPLY
VOLTAGE
NEGATIVE
OUTPUT
VOLTAGE
NEGATIVE VOLTAGE CONVERTER
TOP VIEW
OUT 1
5 C1+
MAX828
IN 2 MAX829
C1- 3
4 GND
SOT23-5
________________________________________________________________ Maxim Integrated Products 1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
http://www.Datasheet4U.com/
1 page  
Switched-Capacitor Voltage Inverters
_______________Detailed Description
The MAX828/MAX829 capacitive charge pumps invert the
voltage applied to their input. For highest performance,
use low equivalent series resistance (ESR) capacitors.
During the first half-cycle, switches S2 and S4 open,
switches S1 and S3 close, and capacitor C1 charges to
the voltage at IN (Figure 2). During the second half-
cycle, S1 and S3 open, S2 and S4 close, and C1 is level
shifted downward by V IN volts. This connects C1 in par-
allel with the reservoir capacitor C2. If the voltage across
C2 is smaller than the voltage across C1, then charge
flows from C1 to C2 until the voltage across C2 reaches -
VIN. The actual voltage at the output is more positive
than -VIN, since switches S1–S4 have resistance and the
load drains charge from C2.
Charge-Pump Output
The MAX828/MAX829 are not voltage regulators: the
charge pump’s output source resistance is approxi-
mately 20Ω at room temperature (with V IN = +5V), and
VOUT approaches -5V when lightly loaded. V OUT will
droop toward GND as load current increases. The
droop of the negative supply (V DROOP-) equals the cur-
rent draw from OUT (I OUT) times the negative convert-
er’s source resistance (RS-):
VDROOP- = IOUT x RS-
The negative output voltage will be:
VOUT = -(VIN - VDROOP-)
Efficiency Considerations
The efficiency of the MAX828/MAX829 is dominated by
its quiescent supply current (I Q) at low output current
and by its output impedance (R OUT) at higher output
current; it is given by:
η
≅
IOUT
IOI UT +
Q
1−
IOUT
x ROUT
VIN
S1
IN
S2
C1
S3 S4
C2
VOUT = -(VIN)
Figure 2. Ideal Voltage Inverter
where the output impedance is roughly approximated
by:
()ROUT ≅
1
fOSC x
C1
++2RSW
4ESRC1 + ESRC2
The first term is the effective resistance of an ideal
switched-capacitor circuit (Figures 3a and 3b), and
RSW is the sum of the charge pump’s internal switch
resistances (typically 8Ω to 9Ω at VIN = +5V). The typical
output impedance is more accurately determined from
the Typical Operating Characteristics.
Applications Information
Capacitor Selection
To maintain the lowest output resistance, use capacitors
with low ESR (Table 1). The charge-pump output resis-
tance is a function of C1’s and C2’s ESR. Therefore,
minimizing the charge-pump capacitor’s ESR minimizes
the total output resistance.
f
V+
C1
VOUT
C2 RL
REQUIV
V+
REQUIV =
1
f × C1
C2
VOUT
RL
Figure 3a. Switched-Capacitor Model
Figure 3b. Equivalent Circuit
_______________________________________________________________________________________ 5
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