Datasheet

TC1240/TC1240A
DS21516D-page 10  2001-2012 Microchip Technology Inc.
5.7 Cascading Devices
Two or more TC1240/TC1240As can be cascaded to
increase output voltage (Figure 5-4). If the output is
lightly loaded, it will be close to ((n + 1) x V
IN
), but will
droop at least by R
OUT
of the first device multiplied by
the I
Q
of the second. It can be seen that the output
resistance rises rapidly for multiple cascaded devices.
For the case of the two-stage ‘tripler’, output resistance
can be approximated as R
OUT
= 2 x R
OUT1
+ R
OUT2
,
where R
OUT1
is the output resistance of the first stage
and R
OUT2
is the output resistance of the second stage.
5.8 Paralleling Devices
To reduce the value of R
OUT
, multiple TC1240/
TC1240As can be connected in parallel (Figure 5-5).
The output resistance will be reduced by a factor of N,
where N is the number of TC1240/TC1240As. Each
device will require its own pump capacitor (C1x), but all
devices may share one reservoir capacitor (C2).
However, to preserve ripple performance, the value of
C2 should be scaled according to the number of
paralled TC1240/TC1240As, respectively.
5.9 Layout Considerations
As with any switching power supply circuit good layout
practice is recommended. Mount components as close
together as possible to minimize stray inductance and
capacitance. Also use a large ground plane to minimize
noise leakage into other circuitry.
FIGURE 5-4: Cascading Multiple Devices To Increase Output Voltage.
FIGURE 5-5: Paralleling Multiple Devices To Reduce Output Resistance.
"n"
C+
GND
C-
OUT
3
2
5
1
6
TC1240
TC1240A
SHDN
4
V
IN
C+
GND
C-
OUT
C
1A
3
2
5
1
6
C
2B
V
IN
V
OUT
V
OUT
= (n + 1)V
IN
TC1240
TC1240A
SHDN
4
"1"
+
+
+
V
IN
C
1B
C
2A
+
C
1A
C
1B
6
4
2
3
2
5
1
1
5
3
C
2
V
OUT
V
OUT
= 2 x V
IN
R
OUT
=
R
OUT
OF SINGLE DEVICE
V
IN
NUMBER OF DEVICES
TC1240
TC1240A
TC1240
TC1240A
. . .
. . .
SHDN
SHDN
Shutdown
Control
4
6
V
IN
+
+
+
"1"
"n"