MAX1044/ICL7660
Switched-Capacitor Voltage Converters
V+
S1
C1
S2
V+
pin 8
S1
CAP+
pin 2
S2
1M
OSCILLATOR
S3
S4
C2
V
OUT
= -(V+)
BOOST
pin 1
OSC
pin 7
Q
2
Q
S3
INTERNAL
REGULATOR
S4
CAP-
pin 4
LV
pin 6
GND
pin 3
V
OUT
pin 5
Figure 2. Ideal Voltage Inverter
Figure 4. MAX1044 and ICL7660 Functional Diagram
Design Information
f
V+
C1
C2
V
OUT
R
LOAD
The MAX1044/ICL7660 are designed to provide a simple,
compact, low-cost solution where negative or doubled
supply voltages are needed for a few low-power com-
ponents. Figure 5 shows the basic negative voltage
converter circuit. For many applications, only two external
capacitors are needed. The type of capacitor used is not
critical.
Proper Use of the Low-Voltage (LV) Pin
Figure 3a. Switched Capacitor Model
R
EQUIV
V+
1
R
EQUIV
=
f x C1
C2
V
OUT
R
LOAD
Figure 4 shows an internal voltage regulator inside
the MAX1044/ICL7660. Use the LV pin to bypass this
regulator, in order to improve low-voltage performance
and allow operation down to 1.5V. For low-voltage opera-
tion and compatibility with the industry-standard LTC1044
and ICL7660, the LV pin should be connected to ground
for supply voltages below 3.5V and left open for supply
voltages above 3.5V.
The MAX1044’s LV pin can be grounded for all operat-
ing conditions. The advantage is improved low-voltage
performance and increased oscillator frequency. The
disadvantage is increased quiescent current and reduced
efficiency at higher supply voltages. For Maxim’s ICL7660,
the LV pin must be left open for supply voltages above 5V.
When operating at low supply voltages with LV open,
connections to the LV, BOOST, and OSC pins should
be short or shielded to prevent EMI from causing
oscillator jitter.
Figure 3b. Equivalent Circuit
where f is one-half the oscillator frequency. This resis-
tance is a major component of the output impedance of
switched-capacitor circuits like the MAX1044/ICL7660.
As shown in Figure 4, the MAX1044/ICL7660 contain
MOSFET switches, the necessary transistor drive cir-
cuitry, and a timing oscillator.
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