 2002 Microchip Technology Inc.

DS21360B-page 7

TC1142

TABLE 3-2:

LOW ESR SURFACE-MOUNT

CAPACITOR

MANUFACTURERS

3.3

Power Efficiency

Assuming the output is loaded with at least 20% of the

maximum available output current, the power efficiency

of the TC1142 can be estimated using the following

equation:

EQUATION 3-5:

an efficiency of approximately 78%. For loads less than

20% of the maximum available output current, the

power efficiency will be substantially reduced. Other

factors that affect the actual efficiency include:

1.

Losses from power consumed by the internal

oscillator (if used).

2.

MOSFET charge pump switches.

3.

Charge pump capacitor losses due to ESR.

4.

Losses that occur during charge transfer (from

the flying capacitors to the output capacitor)

when a voltage difference exists between these

capacitors.

3.4

Choice of -2x or -1x Connections

If required output voltage can be achieved using a -1x

configuration then this is preferred for the following

reasons:

1.

2.

Only one flying capacitor needed

3.

The output ripple becomes proportional to

3.5

Layout Considerations

Proper layout is important to obtain optimal perfor-

mance. Mount capacitors as close to their connecting

device pins as possible to minimize stray inductance

and capacitance. It is recommended that a large

ground plane be used to reduce noise leakage into

other circuitry.

FIGURE 3-4:

TIMING DIAGRAM

Manufacturer

Type

Phone

AVX Corp.

TPS series surface-mount

tantalum

X7R type surface-mount

ceramic

803-448-9411

Matsuo

267 series surface-mount

tantalum

X7R type surface-mount

ceramic

714-969-2491

Sprague

593D, 594D, 595D series

surface-mount tantalum

207-324-4140

Murata

Ceramic chip capacitors

800-831-9172

Taiyo Yuden

Ceramic chip capacitors

800-348-2496

Tokin

Ceramic chip capacitors

408-432-8020

CCLK

Internal

Oscillator

Shutdown

External

Clock

Shutdown

GND