Charge Pump
The charge pump is a Sipex–patented design
(#5,306,954) and uses a unique approach compared
to older, less–efficient designs. The charge
pump still requires four external capacitors, but
uses a four–phase voltage shifting technique to
attain symmetrical 5.5V power supplies. The
internal power supply consists of a regulated
dual charge pump that provides output voltages
of 5.5V regardless of the input voltage (VCC)
over the +3.0V to +5.5V range.
In most circumstances, decoupling the power
supply can be achieved adequately using a 0.1μF
bypass capacitor at C5 (refer to Figures 6 and 7).
In applications that are sensitive to power-supply
noise, decouple VCC to ground with a capacitor
of the same value as charge-pump capacitor
C1. Physically connect bypass capacitors as
close to the IC as possible.
The charge pumps operate in a discontinuous
mode using an internal oscillator. If the output
voltages are less than a magnitude of 5.5V, the
charge pumps are enabled. If the output voltage
exceed a magnitude of 5.5V, the charge pumps
are disabled. This oscillator controls the four
phases of the voltage shifting. A description of
each phase follows.
楼主
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原来你们说的是C1-C5的电容，受到另一篇问USB线上电容的影响，我一直以为楼主问的是TXD和RXD上的电容。
