Positive Doubling Charge Pump with
Shutdown in SOT Package
TC1240
R
OUT
=
R
OUT
OF SINGLE DEVICE
NUMBER OF DEVICES
V
IN
1
3
2
6
4
TC1240
C1B
3
TC1240
2
"n"
6
4 SHDN
...
C2
Shutdown
Control
5
...
1
V
IN
However, to preserve ripple performance the value of C2
should be scaled according to the number of paralleled
TC1240s.
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.
C1A
"1"
SHDN
5
V
OUT
TC1240 DEMO CARD
V
OUT =
2 x V
IN
Figure 5. Paralleling Multiple Devices to Reduce Output Resistance
PARALLELING DEVICES
To reduce the value of R
OUT
, multiple TC1240s can be
connected in parallel (Figure 5). The output resistance will
be reduced by a factor of N where N is the number of
TC1240s. Each device will require its own pump capacitor
(C1x), but all devices may share one resevoir capacitor (C2).
The TC1240 Demo Card is a 1.25” x 1.0” card contain-
ing a TC1240 and all of the necessary external components
that allow the user to evaluate the device’s ability to gener-
ate a 2X non-regulated output voltage. The demo card is
fully assembled with the required external capacitors along
with a variable load resistor that allows the user to vary the
output load current of the output stage. For convenience,
several test points and jumpers are available for measuring
various voltages and currents on the circuit board.
Figure 6. TC1240 Demo Card Schematic
TC1240-1 7/7/00
5
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