ICL7660ISA View Datasheet(PDF) - Maxim Integrated
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ICL7660ISA Datasheet PDF : 14 Pages
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MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Increasing Efficiency
Efficiency can be improved by lowering output voltage
ripple and output impedance. Both output voltage ripple
and output impedance can be reduced by using large
capacitors with low ESR.
The output voltage ripple can be calculated by noting that
the output current is supplied solely from capacitor C2
during one-half of the charge-pump cycle.
VRIPPLET
≅
2
×
1
fOSC
x
C2
+
2
x
ESR C2
IOUT
Slowing the oscillator frequency reduces quiescent
current. The oscillator frequency can be reduced by
connecting a capacitor to the OSC pin.
Reducing the oscillator frequency increases the rip-
ple voltage in the MAX1044/ICL7660. Compensate by
increasing the values of the bucket and reservoir capaci-
tors. For example, in a negative voltage converter, the
pump frequency is around 4kHz or 5kHz. With the rec-
ommended 10μF bucket and reservoir capacitors, the
circuit consumes about 70μA of quiescent current while
providing 20mA of output current. Setting the oscillator to
400Hz by connecting a 100pF capacitor to OSC reduces
the quiescent current to about 15μA. Maintaining 20mA
output current capability requires increasing the bucket
and reservoir capacitors to 100μF.
Note that lower capacitor values can be used for lower
output currents. For example, setting the oscillator to
40Hz by connecting a 1000pF capacitor to OSC provides
the highest efficiency possible. Leaving the bucket and
reservoir capacitors at 100μF gives a maximum IOUT of
2mA, a no-load quiescent current of 10μA, and a power
conversion efficiency of 98%.
General Precautions
1) Connecting any input terminal to voltages greater
than V+ or less than ground may cause latchup. Do
not apply any input sources operating from external
supplies before device power-up.
2) Never exceed maximum supply voltage ratings.
3) Do not connect C1 and C2 with the wrong polarity.
4) Do not short V+ to ground for extended periods with
supply voltages above 5.5V present on other pins.
5) Ensure that VOUT (pin 5) does not go more positive
than GND (pin 3). Adding a diode in parallel with C2,
with the anode connected to VOUT and cathode to LV,
will prevent this condition.
Application Circuits
Negative Voltage Converter
Figure 8 shows a negative voltage converter, the most
popular application of the MAX1044/ICL7660. Only two
external capacitors are needed. A third power-supply
bypass capacitor is recommended (0.1μF to 10μF)
+
1 BOOST
8
V+
2
MAX1044
7
CBYPASS
0.1µF
C1
ICL7660
10µF
3
6
4
LV 5
VOUT = -(V+)
C2
10µF
Figure 8. Negative Voltage Converter with BOOST and LV
Connections
+
1
8
2
MAX1044
ICL7660
7
3
6
4
5
V+
VOUT = 2(V+) - 2VD
C1
C2
Figure 9. Voltage Doubler
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