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PDF MAX829EUK Data sheet ( Hoja de datos )
| Número de pieza | MAX829EUK | |
| Descripción | Switched-Capacitor Voltage Inverters | |
| Fabricantes | Maxim Integrated | |
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19-0495; Rev 2; 4/97
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 applications 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
TEMP. RANGE
MAX828C/D
MAX828EUK
MAX829C/D
MAX829EUK
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
* Dice are tested at TA = +25°C.
PIN-
PACKAGE
Dice*
5 SOT23-5
Dice*
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 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  
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 VIN 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 VIN = +5V), and
VOUT approaches -5V when lightly loaded. VOUT will
droop toward GND as load current increases. The
droop of the negative supply (VDROOP-) equals the cur-
rent draw from OUT (IOUT) 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 power efficiency of a switched-capacitor voltage
converter is affected by three factors: the internal loss-
es in the converter IC, the resistive losses of the pump
capacitors, and the conversion losses during charge
transfer between the capacitors. The total power loss is:
ΣPLOSS = PINTERNAL LOSSES + PSWITCH LOSSES
+ PPUMP CAPACITOR LOSSES
+ PCONVERSION LOSSES
S1
IN
S2
C1
S3 S4
C2
VOUT = -(VIN)
Figure 2. Ideal Voltage Inverter
The internal losses are associated with the IC’s internal
functions, such as driving the switches, oscillator, etc.
These losses are affected by operating conditions such
as input voltage, temperature, and frequency.
The next two losses are associated with the voltage
converter circuit’s output resistance. Switch losses
occur because of the on-resistance of the MOSFET
switches in the IC. Charge-pump capacitor losses
occur because of their ESR. The relationship between
these losses and the output resistance is as follows:
PPUMP CAPACITOR LOSSES + PCONVERSION LOSSES
= IOUT2 x ROUT
( ) ( )ROUT ≅
1
fOSC x
C1 + 4 2RSWITCHES + ESRC1
+ ESRC2
where fOSC is the oscillator frequency. The first term is
the effective resistance from an ideal switched-
capacitor circuit. See Figures 3a and 3b.
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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