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PDF MAX1852 Data sheet ( Hoja de datos )
| Número de pieza | MAX1852 | |
| Descripción | SC70 Inverting Charge Pumps with Shutdown | |
| Fabricantes | Maxim Integrated | |
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19-1792; Rev 0; 9/00
SC70 Inverting Charge Pumps
with Shutdown
General Description
The MAX1852/MAX1853 monolithic, CMOS charge-
pump voltage inverters in the ultra-small SC70 package
feature a low 15Ω output resistance, permitting loads
up to 30mA with maximum efficiency. The MAX1852/
MAX1853 are available with operating frequencies of
50kHz and 200kHz, respectively, allowing optimization
of supply current or external component size. Small
external components and micropower shutdown mode
make these devices ideal for both battery-powered and
board-level voltage conversion applications.
Oscillator control circuitry and four power-MOSFET
switches are included on-chip. Applications include
generating a negative supply from a +5V or +3.3V logic
supply to power analog circuitry. Both versions come in
a 6-pin SC70 package that is 40% smaller than a
SOT23.
Features
o 30mA Output Current
o Low 15Ω Output Resistance
o 68µA Supply Current (MAX1852)
o Requires Only Two 0.68µF Capacitors (MAX1853)
o +2.5V to +5.5V Input Voltage Range
o 0.1µA Logic-Controlled Shutdown
o Two Switching Frequencies
50kHz (MAX1852)
200kHz (MAX1853)
o Slew-Rate Limited to Reduce EMI
o Ultra-Small 6-Pin SC70 Package
Applications
Negative Supply from +5V or +3.3V Logic Supplies
Small LCD Panels
GaAsFET Bias Supplies
Handy-Terminals, PDAs
Battery-Operated Equipment
PART
MAX1852EXT
MAX1853EXT
Ordering Information
TEMP.
RANGE
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
6 SC70
6 SC70
TOP
MARK
AAL
AAM
Typical Operating Circuit
0.68µF
INPUT
2.5V TO 5.5V
C1+
IN
C1-
OUT
MAX1853
ON SHDN
OFF
GND
NEGATIVE
OUTPUT
-1 ✕ VIN
30mA
0.68µF
Pin Configuration
TOP VIEW
OUT 1
6 C1+
MAX1852
GND 2 MAX1853 5 C1-
SHDN 3
4 IN
SC70-6
________________________________________________________________ Maxim Integrated Products 1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
1 page  
SC70 Inverting Charge Pumps
with Shutdown
Pin Description
PIN NAME
FUNCTION
1
OUT
Inverting Charge-Pump Output
2 GND Ground
Shutdown Input. Drive this pin high
3 SHDN for normal operation; drive it low for
shutdown mode.
4
IN
Power-Supply Voltage Input. Input
range is +2.5V to +5.5V.
5
C1-
Negative Terminal of the Flying
Capacitor
6
C1+
Positive Terminal of the Flying
Capacitor
Detailed Description
The MAX1852/MAX1853 charge pumps invert the volt-
age applied to their input. For highest performance use
low equivalent series resistance (ESR) capacitors (e.g.,
ceramic).
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, 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.
Efficiency Considerations
The efficiency of the MAX1852/MAX1853 is dominated
by their quiescent supply current (IQ) at low output cur-
rent and by their output impedance (ROUT) at higher
output current; it is given by:
η≅
IOUT
1−
IOUT
x
ROUT
IOUT + IQ
VIN
where the output impedance is roughly approximated
by:
( )ROUT ≅ 1 + 2RSW + 4ESRC1 + ESRC2
fOSC x C1
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
C1
INPUT
2.5V TO 5.5V
C3
ON
OFF
TE: (
6
4 C1+
IN
5
C1- 1
OUT
3 SHDN
MAX1852
MAX1853
GND
2
RL
Figure 1. Typical Application Circuit
NEGATIVE
OUTPUT
-1 ✕ VIN
C2
resistances (typically 6Ω at VIN = +5V). The typical out-
put impedance is more accurately determined from the
Typical Operating Characteristics.
Shutdown
The MAX1852/MAX1853 have a logic-controlled shut-
down input. Driving SHDN low places the devices in a
low-power shutdown mode. The charge-pump switch-
ing halts, supply current is reduced to 2nA.
Driving SHDN high will restart the charge pump. The
switching frequency and capacitor values determine how
soon the device will reach 90% of the input voltage.
Applications Information
Capacitor Selection
The charge-pump output resistance is a function of the
ESR of C1 and C2. To maintain the lowest output resis-
tance, use capacitors with low ESR. (See Table 1 for a
list of recommended manufacturers.) Tables 2 and 3
suggest capacitor values for minimizing output resis-
tance or capacitor size.
Flying Capacitor (C1)
Increasing the flying capacitor’s value reduces the out-
put resistance. Above a certain point, increasing C1’s
capacitance has negligible effect because the output
resistance is then dominated by internal switch resis-
tance and capacitor ESR.
Output Capacitor (C2)
Increasing the output capacitor’s value reduces the
output ripple voltage. Decreasing its ESR reduces both
output resistance and ripple. Lower capacitance values
can be used with light loads if higher output ripple can
be tolerated. Use the following equation to calculate the
peak-to-peak ripple:
_______________________________________________________________________________________ 5
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| PDF Descargar | [ Datasheet MAX1852.PDF ] | |
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