SP3243EBCA-L-TR Datasheet, PDF (11/25 Pages) Exar Corporation – 3 Driver/5 Receiver Intelligent +3.0V to +5.5V RS-232 Transceivers

Minimum recommended charge pump capacitor value
Input Voltage Vcc
Charge pump capacitor value for SP32XX
3.0V to 3.6V
C1 - C4 = 0.1µF
4.5V to 5.5V
C1 = 0.047µF, C2 - C4 = 0.33µF
3.0V to 5.5V
C1 - C4 = 0.22µF
The Exar-patented charge pumps are designed
to operate reliably with a range of low cost
capacitors. Either polarized or non polarized
capacitors may be used. If polarized capacitors
are used they should be oriented as shown in
the Typical Operating Circuit. The V+ capaci-
tor may be connected to either ground or Vcc
(polarity reversed.)
The charge pump operates with 0.1µF capacitors
for 3.3V operation. For other supply voltages, see
the table for required capacitor values. Do not use
values smaller than those listed. Increasing the
capacitor values (e.g., by doubling in value)
The SP3243E devices have a patent pending
AUTO ON-LINE^® circuitry on board that saves
power in applications such as laptop computers,
palmtop (PDA) computers and other portable
systems.
The SP3243E devices incorporate an AUTO
ON-LINE^® circuit that automatically enables itself
when the external transmitters are enabled and
the cable is connected. Conversely, the AUTO
ON-LINE^® circuit also disables most of the inter-
nal circuitry when the device is not being used
and goes into a standby mode where the device
typically draws 1µA. This function is externally
controlled by the ONLINE pin. When this pin is
tied to a logic LOW, the AUTO ON-LINE^® function
is active. Once active, the device is enabled until
there is no activity on the receiver inputs. The
receiver input typically sees at least +3V, which
are generated from the transmitters at the other
end of the cable with a +5V minimum.
reduces ripple on the transmitter outputs and
may slightly reduce power consumption. C2,
C3, and C4 can be increased without changing
C1’s value.
For best charge pump efficiency locate the
charge pump and bypass capacitors as close
as possible to the IC. Surface mount capacitors
are best for this purpose. Using capacitors with
lower equivalent series resistance (ESR) and
self-inductance, along with minimizing parasitic
PCB trace inductance will optimize charge pump
operation. Designers are also advised to consider
that capacitor values may shift over time and
operating temperature.
AUTO ONLINE CIRCUITRY
When the external transmitters are disabled or
the cable is disconnected, the receiver inputs will
be pulled down by their internal 5kΩ resistors to
ground. When this occurs over a period of time,
the internal transmitters will be disabled and the
device goes into a shutdown or standy mode.
When ONLINE is HIGH, the AUTO ON-LINE^®
mode is disabled.
The AUTO ON-LINE^® circuit has two stages:
1) Inactive Detection
2) Accumulated Delay
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
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