TC1142 datasheet(7/12 Pages) MICROCHIP

7 / 12 page

 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:

For example, a 3.2 Volt VIN, and a -5 Volt VR will have

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:

Losses from power consumed by the internal

oscillator (if used).

I2R losses due to the on-resistance of the

MOSFET charge pump switches.

Charge pump capacitor losses due to ESR.

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:

Power efficiency is improved from VR/2VIN to

VR/VIN

Only one flying capacitor needed

The output ripple becomes proportional to

VIN – VR rather than 2 VIN – VR.

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

η = |VR|

2(VIN)

CCLK

VOUT

–VR

Internal

Oscillator

Shutdown

External

Clock

Shutdown

t0 = counter timeout (~160 µsec)

VIL

GND

VIH

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