SP3281EB Datasheet, PDF (10/15 Pages) Sipex Corporation – Intelligent +2.35V to +5.5V RS-232 Transceivers

Delay
Stage
Delay
Stage
Delay
Stage
R₁ INACT
R₂ INACT
R₃ INACT
STATUS
Figure 16. Stage II of AUTO ON-LINE^® Circuitry
SHUTDOWN ONLINE
INPUT
INPUT
RS-232 SIGNAL AT
RECEIVER INPUT
STATUS
OUTPUT
T_XOUT
R_XOUT
TRANSCEIVER
STATUS
HIGH
-
YES
HIGH Active Active
Normal
Operation
HIGH
HIGH
NO
LOW Active Active
Normal
Operation
AUTO ON-LINE^®
HIGH
LOW
NO
LOW High-Z Active
Mode
LOW
-
YES
HIGH High-Z High-Z
Shutdown
LOW
-
NO
Table 3. AUTO ON-LINE^® Logic
LOW High-Z High-Z
Shutdown
AUTO ON-LINE^® Circuitry
The SP3281EB device has 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 SP3281EB device incorporates 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 internal circuitry when the device is not
being used and goes into a standby mode where the
device typically draws 1µA. This function is
controlled by the ONLINE pin. When this pin is
tied to a logic LOW, the AUTO ON-LINE^® func-
tion 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. 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 standby 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
The first stage, shown in Figure 15, detects an
inactive input. A logic HIGH is asserted on
R_XINACT if the cable is disconnected or the
Rev. 6/19/03
SP3281EB Intelligent +2.35V to +5.5V RS-232 Transceivers
10
© Copyright 2003 Sipex Corporation