5

TC1240

Positive Doubling Charge Pump with

Shutdown in SOT Package

TC1240-1 7/7/00 DS21333A

© 2001 Microchip Technology Inc.

Figure 5. Paralleling Multiple Devices to Reduce Output Resistance

C1A

C1B

6

6

2

3

2

5

1

1

5

3

C2

V

OUT

V

R

R

OUT

OF SINGLE DEVICE

V

IN

NUMBER OF DEVICES

TC1240

"1"

TC1240

"n"

. . .

. . .

SHDN

SHDN

Shutdown

Control

4

4

V

IN

PARALLELING DEVICES

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).

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.

TC1240 DEMO CARD

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