© 2005 Microchip Technology Inc.

DS21486C-page 9

TCM680

5.3

Paralleling Devices

OUT

TCM680 voltage converters can be connected in paral-

lel (Figure 5-2). The output resistance of both outputs

will be reduced, approximately, by a factor of n, where

n is the number of devices connected in parallel.

EQUATION

EQUATION

Each device requires its own pump capacitors, but all

devices may share the same reservoir capacitors. To

preserve ripple performance, the value of the reservoir

capacitors should be scaled according to the number of

devices connected in parallel.

5.4

Output Voltage Regulation

The outputs of the TCM680 can be regulated to provide

+5V from a 3V input source (Figure 5-3). The TCM680

performs voltage multiplication and inversion produc-

ing output voltages of, approximately, +6V. The

TCM680 outputs are regulated to +5V with the linear

regulators TC55 and TC59. The TC54 is a voltage

detector providing an indication that the input source is

low and that the outputs may fall out of regulation. The

input source to the TCM680 can vary from 2.8V to 5.5V

without adversely affecting the output regulation mak-

ing this application well suited for use with single cell

Li-Ion batteries or three alkaline or nickel based

batteries connected in series.

FIGURE 5-2:

Paralleling TCM680 for Lower Output Source Resistance.

OUT

n (number of devices)

OUT

n (number of devices)

10 µF

10 µF

22 µF

GND

GND

Supply

TCM680

TCM680

+

–

+

–

+

–

+

–

+

–

+

+

-

-

-

-

10 µF

10 µF

GND

+

+

-

-

Negative

Supply

Positive

22 µF

+

–

+

+