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PDF ( 数据手册 , 数据表 ) MAX1681

零件编号 MAX1681
描述 Switched-Capacitor Voltage Converters
制造商 Maxim Integrated
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MAX1681 数据手册, 描述, 功能
19-1247; Rev 0; 7/97
125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters
_______________General Description
The MAX1680/MAX1681 inductorless switched-capaci-
tor voltage converters either invert an input voltage of
+2.0V to +5.5V or double it while supplying up to
125mA output current. They have a selectable-frequen-
cy option that allows the use of small capacitors: 4.7µF
(MAX1680), 1µF (MAX1681). With their high output cur-
rent capability, these charge-pump devices are suit-
able replacements for inductor-based regulators, which
require more expensive external components and addi-
tional board space.
The devices’ equivalent output resistance (typically
3.5) allows them to deliver as much as 125mA with
only a 440mV drop. A shutdown feature reduces quies-
cent current to less than 1µA. The MAX1680/MAX1681
are available in 8-pin SO packages. For devices that
deliver up to 50mA in smaller µMAX packages, refer to
the MAX860/MAX861 data sheet.
____________________________Features
o Selectable Switching Frequencies:
125kHz/250kHz (MAX1680)
500kHz/1MHz (MAX1681)
o Allow Use of Small Capacitors
(1µF for the MAX1681)
o 125mA Output Current
o 3.5Output Impedance
o 1µA Logic-Controlled Shutdown
o Configurable as Voltage Inverters or Doublers
o +2.0V to +5.5V Input Voltage Range
o Available in 8-Pin SO Packages
o 90% Efficiency
________________________Applications
Local Negative Supplies
Interface Power Supplies
Op-Amp Power Supplies
MOSFET Bias
______________Ordering Information
PART
MAX1680C/D
MAX1680ESA
MAX1681C/D
MAX1681ESA
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
*Contact factory for dice specifications.
PIN-PACKAGE
Dice*
8 SO
Dice*
8 SO
Pin Configuration appears at end of data sheet.
__________________________________________________Typical Operating Circuits
FSEL IN
CAP+ SHDN
+VINPUT
+3V TO +5.5V
1µF
FSEL
CAP+
IN
SHDN
C2
1µF
DOUBLED
OUTPUT
VOLTAGE
C1
MAX1681
C1
1µF
GND LV
INVERTED
1µF
+VINPUT
+4V TO +5.5V
MAX1681
LV
GND
CAP- OUT
OUTPUT
C2 VOLTAGE
1µF
CAP- OUT
1µF
INVERTER CONFIGURATION
NOTE: USE 4.7µF CAPACITORS FOR MAX1680
INPUT VOLTAGE RANGE: +2.0V TO +5.5V.
DOUBLER CONFIGURATION
NOTE: USE 4.7µF CAPACITORS FOR MAX1680
INPUT VOLTAGE RANGE: +2.5V TO +5.5V.
________________________________________________________________ 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.
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MAX1681 pdf, 数据表
125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters
Table 4. Minimum Recommended Capacitances for Maximum Output Current
fOSC (kHz)
125
250
500
1000
VIN = 2V
2.5
1.2
0.6
0.3
CAPACITANCE (µF) (C1 = C2)
VIN = 3V
VIN = 4V
3.8 5.1
1.9 2.5
0.9 1.2
0.4 0.6
VIN = 5V
6.4
3.2
1.6
0.8
+VINPUT
1µF
FSEL
CAP+
IN
SHDN
MAX1681
1µF GND LV
CAP- OUT
VOUT = -VINPUT
1µF
FSEL IN
CAP+ SHDN
1µF MAX1681
LV
GND
CAP- OUT
VOUT = -2VINPUT
1µF
NOTE: USE 4.7µF CAPACITORS FOR MAX1680.
Figure 1. Cascading MAX1680/MAX1681s to Increase Output Voltage
Bypass Capacitor
Bypass the input voltage to reduce AC impedance and
to prevent internal switching noise. Bypassing depends
on the source impedance location. The AC ripple cur-
rent is 2 x IOUT for the doubler and the inverter. Use a
large bypass capacitor (equal to C1) if the supply has
high AC impedance.
Cascading Devices
To produce larger negative voltages, cascade two
devices (Figure 1). For two devices, the unloaded out-
put voltage is approximately -2 x VINPUT, but this value
is reduced slightly by the first device’s output resis-
tance multiplied by the second device’s quiescent cur-
rent. The effective output resistance for a cascaded
device is larger than that for an individual device (20
for two devices). Cascading several devices increases
output resistance and reduces efficiency. If a large
negative voltage is required for several stages, an
inductive inverting switching regulator such as the
MAX629 or MAX774 may offer more advantages.
Paralleling Devices
Parallel two or more MAX1680/MAX1681s to reduce
output resistance voltage drop under a given load. With
reduced output resistance, paralleled devices deliver
higher load currents. Figure 2 shows two
MAX1680/MAX1681s connected in parallel. Output
resistance is inversely proportional to the number of
devices.
8 _______________________________________________________________________________________
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