SP3223 Sipex, SP3223 Datasheet - Page 17

• Manufacturer Part Number: SP3223
• Description: Intelligent +3.0V to +5.5V RS-232 Transceivers
• Manufacturer: Sipex

AUTO ON-LINE
The SP3223 and SP3243 devices have a patent
pending AUTO ON-LINE
that saves power in applications such as laptop
computers, palmtop (PDA) computers, and other
portable systems.
The SP3223 and SP3243 devices incorporate an
AUTO ON-LINE
enables itself when the external transmitters are
enabled and the cable is connected. Conversely,
the AUTO ON-LINE
most of the internal circuitry when the device is
not being used and goes into a standby mode
where the device typically draws 1µA. This
function can also be externally controlled by the
ONLINE pin. When this pin is tied to a logic
LOW, the AUTO ON-LINE
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. 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
The first stage, shown in Figure 23, detects an
inactive input. A logic HIGH is asserted on
R
external transmitters are disabled. Otherwise,
R
is duplicated for each of the other receivers.
Rev. 6/30/03
X
X
INACT if the cable is disconnected or the
INACT will be at a logic LOW. This circuit
1) Inactive Detection
2) Accumulated Delay
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Circuitry
circuit that automatically
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circuit has two stages:
circuit also disables
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circuitry on board
function is active.
SP3223 +3.0V to +5.5V RS-232 Transceivers
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17
The second stage of the AUTO ON-LINE
circuitry, shown in Figure 24, processes all the
receiver's R
lated delay that disables the device to a 1µA
supply current.
The STATUS pin goes to a logic LOW when the
cable is disconnected, the external transmitters
are disabled, or the SHUTDOWN pin is
invoked. The typical accumulated delay is
around 20µs.
When the SP3223 and SP3243 drivers or inter-
nal charge pump are disabled, the supply current
is reduced to 1µA. This can commonly occur in
hand-held or portable applications where the
RS-232 cable is disconnected or the RS-232
drivers of the connected peripheral are turned off.
The AUTO ON-LINE
by the SHUTDOWN pin. If this pin is a logic
LOW,the AUTO ON-LINE
operate regardless of the logic state of the
ONLINE pin. Table 3 summarizes the logic of the
AUTO ON-LINE
table logic of the SP3223 and SP3243 driver and
receiver outputs can be found in Table 2.
The STATUS pin outputs a logic LOW signal
if the device is shutdown. This pin goes to a
logic HIGH when the external transmitters are
enabled and the cable is connected.
When the SP3223 and SP3243 devices
are shut down, the charge pumps are turned off.
V+ charge pump output decays to V
V- output decays to GND. The decay time will
depend on the size of capacitors used for the
charge pump. Once in shutdown, the time
required to exit the shut down state and have
valid V+ and V- levels is typically 200µs.
For easy programming, the STATUS can be
used to indicate DTR or a Ring Indicator signal.
Tying ONLINE and SHUTDOWN together
will bypass the AUTO ON-LINE
this connection acts like a shutdown input pin.
X
INACT signals with an accumu-
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operating modes. The truth
© Copyright 2003 Sipex Corporation
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mode can be disabled
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function will not
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circuitry so
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, the
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