Datasheet

 2002-2011 Microchip Technology Inc. DS21465C-page 7
TC7660
5.0 APPLICATIONS INFORMATION
5.1 Simple Negative Voltage
Converter
Figure 5-1 shows typical connections to provide a
negative supply where a positive supply is available. A
similar scheme may be employed for supply voltages
anywhere in the operating range of +1.5V to +10V,
keeping in mind that pin 6 (LV) is tied to the supply
negative (GND) only for supply voltages below 3.5V.
FIGURE 5-1: Simple Negative Converter.
The output characteristics of the circuit in Figure 5-1
are those of a nearly ideal voltage source in series with
a 70resistor. Thus, for a load current of -10 mA and
a supply voltage of +5V, the output voltage would be
-4.3V.
5.2 Paralleling Devices
To reduce the value of R
OUT
, multiple TC7660 voltage
converters can be connected in parallel (Figure 5-2).
The output resistance will be reduced by approximately
a factor of n, where n is the number of devices
connected in parallel.
EQUATION
While each device requires its own pump capacitor
(C
1
), all devices may share one reservoir capacitor
(C
2
). To preserve ripple performance, the value of C
2
should be scaled according to the number of devices
connected in parallel.
5.3 Cascading Devices
A larger negative multiplication of the initial supply volt-
age can be obtained by cascading multiple TC7660
devices. The output voltage and the output resistance
will both increase by approximately a factor of n, where
n is the number of devices cascaded.
EQUATION
FIGURE 5-2: Paralleling Devices Lowers Output Impedance.
FIGURE 5-3: Increased Output Voltage By Cascading Devices.
+
V
+
+
1
2
3
4
8
7
6
5
TC7660
V
OUT
*
C
1
10 µF
* V
OUT
= -V
+
for 1.5V  V+  10V
C
2
10 µF
R
OUT
R
OUT
of TC7660
n number of devices
---------------------------------------------------------=
V
OUT
n– V
+
=
R
OUT
nR
OUT
of TC7660=
“n”
“1”
R
L
+
V
+
+
1
2
3
4
8
7
6
5
TC7660
C
1
C
2
+
1
2
3
4
8
7
6
5
TC7660
C
1
V
OUT
*
“1”
+
V
+
+
1
2
3
4
8
7
6
5
TC7660
10 µF
* V
OUT
= -n V
+
for 1.5V  V+  10V
“n”
+
1
2
3
4
8
7
6
5
TC7660
10 µF
10 µF
+
10 µF