SP6660DS/11 SP6660 200mA Charge Pump Inverter or Doubler © Copyright 2000 Sipex Corporation
12
THEORY OF OPERATION
Negative Voltage Inverter
This is the most common application of the
SP6660 where a +1.5V to +4.25V input is
converted to a -1.5V to -4.25V output. In the
inverting mode, the SP6660 is typically operated
with LV connected to GND. Since the LV may
be left open, the substitution of the SP6660 for
the ICL7660 industry standard is simplified.
The circuit for the voltage inverter mode can be
found in Figure 21. This operating circuit uses
only two external capacitors, C1 and C2, for
the internal charge pump. This allows designers
to avoid any EMI concerns with the costly,
space-consuming inductors typically used with
switching regulators.
Figure 21. Typical Operating Circuit for the Voltage Inverter
OSC
OUT
SP6660
+V
IN
+1.5V to +4.25V
C1
1µF to 150µF
5
1
2
7
4
FC
C2
1µF to 150µF
CAP+
CAP-
GND
6
8
3
LV
NEGATIVE
VOLTAGE
OUTPUT
TYPICAL CIRCUIT: VOLTAGE INVERTER
+V
The SP6660 is insensitive to load current
changes. Output Source Resistance vs. Supply
Voltage and Temperature curves are shown in
Figures 14 to 16. A typical output source
resistance of 5.2Ω allows an output voltage of
-4.25V under light load with an input of +4.25V.
This output voltage decreases to only -4.0V
with a load current draw of 100mA.
The peak-to-peak output ripple voltage is
calculated as follows:
V
RIPPLE
=
+ I
OUT
(ESRC2)
I
OUT
2(f
PUMP
)(C2)
