Datasheet

 2002-2011 Microchip Technology Inc. DS21465C-page 9
TC7660
FIGURE 5-7: Combined Negative
Converter and Positive Multiplier.
5.7 Efficient Positive Voltage
Multiplication/Conversion
Since the switches that allow the charge pumping
operation are bidirectional, the charge transfer can be
performed backwards as easily as forwards.
Figure 5-8 shows a TC7660 transforming -5V to +5V
(or +5V to +10V, etc.). The only problem here is that the
internal clock and switch-drive section will not operate
until some positive voltage has been generated. An ini-
tial inefficient pump, as shown in Figure 5-7, could be
used to start this circuit up, after which it will bypass the
other (D
1
and D
2
in Figure 5-7 would never turn on), or
else the diode and resistor shown dotted in Figure 5-8
can be used to “force” the internal regulator on.
FIGURE 5-8: Positive Voltage
Conversion.
+
C
1
D
1
+
+
C
3
C
4
C
2
D
2
+
V
OUT
=
1
2
3
4
8
7
6
5
TC7660
V
+
(2 V
+
) - (2 V
F
)
V
OUT
= -V
+
V
OUT
= -V
-
+
1M
V
-
input
+
1
2
3
4
8
7
6
5
TC7660
10 µF
10 µF
C
1