TC1142 Просмотр технического описания (PDF) - Microchip Technology
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TC1142 Datasheet PDF : 12 Pages
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TC1142
TABLE 3-2:
LOW ESR SURFACE-MOUNT
CAPACITOR
MANUFACTURERS
Manufacturer
Type
Phone
AVX Corp.
Matsuo
Sprague
Murata
Taiyo Yuden
Tokin
TPS series surface-mount 803-448-9411
tantalum
X7R type surface-mount
ceramic
267 series surface-mount 714-969-2491
tantalum
X7R type surface-mount
ceramic
593D, 594D, 595D series 207-324-4140
surface-mount tantalum
Ceramic chip capacitors 800-831-9172
Ceramic chip capacitors 800-348-2496
Ceramic chip capacitors 408-432-8020
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:
η = |VR|
2(VIN )
FIGURE 3-4:
TIMING DIAGRAM
t0
VIH
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:
1. Losses from power consumed by the internal
oscillator (if used).
2. I2R losses due to the on-resistance of the
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. Power efficiency is improved from VR/2VIN to
VR/VIN
2. Only one flying capacitor needed
3. 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.
t0
VIL
CCLK
VOUT GND
–VR
Internal
Oscillator
t0 = counter timeout (~160 µsec)
Shutdown
External
Clock
Shutdown
2002 Microchip Technology Inc.
DS21360B-page 7
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