tc1240a Microchip Technology Inc., tc1240a Datasheet - Page 10

• Manufacturer Part Number: tc1240a
• Description: Positive Doubling Charge Pumps With Shutdown In A Sot-23 Package
• Manufacturer: Microchip Technology Inc.

TC1240/TC1240A
5.7
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
droop at least by R
the I
resistance rises rapidly for multiple cascaded devices.
For the case of the two-stage ‘tripler’, output resistance
can be approximated as R
where R
and R
FIGURE 5-4:
FIGURE 5-5:
DS21516C-page 10
Q
OUT2
of the second. It can be seen that the output
OUT1
Cascading Devices
is the output resistance of the second stage.
is the output resistance of the first stage
Shutdown
OUT
C
Control
C
1A
Cascading Multiple Devices To Increase Output Voltage.
1A
Paralleling Multiple Devices To Reduce Output Resistance.
of the first device multiplied by
+
OUT
+
= 2 x R
6
2
3
4
3
2
6
4
C+
GND
C-
SHDN
SHDN
OUT1
TC1240A
TC1240A
TC1240
TC1240
"1"
IN
"1"
+ R
), but will
OUT
OUT2
V
IN
1
5
,
+
V
R
1
5
C
IN
OUT
V
1B
IN
C
2A
=
+
+
5.8
To reduce the value of R
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
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.
C
R
. . .
. . .
1B
OUT
NUMBER OF DEVICES
2
6
3
4
V
3
2
6
4
OUT
C+
GND
C-
SHDN
OF SINGLE DEVICE
SHDN
V
TC1240A
OUT
TC1240A
TC1240
= (n + 1)V
TC1240
Paralleling Devices
Layout Considerations
"n"
"n"
= 2 x V
OUT
V
IN
IN
IN
1
5
+
1
5
+
 2003 Microchip Technology Inc.
C
C
2B
2
V
V
OUT
V
OUT
IN
OUT
, multiple TC1240/