TC1240ECH datasheet(10/18 Pages) MICROCHIP

10 / 18 page

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 VIN), but will

droop at least by ROUT of the first device multiplied by

the IQ 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 ROUT = 2 x ROUT1 + ROUT2,

where ROUT1 is the output resistance of the first stage

and ROUT2 is the output resistance of the second stage.

5.8

Paralleling Devices

To reduce the value of ROUT, 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

TC1240

TC1240A

SHDN

VIN

C+

GND

C-

OUT

C1A

C2B

VIN

VOUT

VOUT = (n + 1)VIN

TC1240

TC1240A

SHDN

"1"

VIN

C1B

C2A

C1A

C1B

VOUT

VOUT = 2 x VIN

ROUT =

ROUT OF SINGLE DEVICE

VIN

NUMBER OF DEVICES

TC1240

TC1240A

TC1240

TC1240A

. . .

SHDN

Shutdown

Control

VIN

"1"

"n"

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