SP503AN Datasheet, PDF (8/13 Pages) Sipex Corporation – Application Note

Typical Applications Questions
on the SP503
Can the SP503 be used with external power
supplies? If so, is there a power-up sequence?
The internal charge pump can be bypassed
through external supplies to V_DD and V_SS. The
external voltage should be +10V for V_DD and
-10V for V_SS. The tolerance is ±5%. The
absolute minimum limit for the external supplies
is ±7V and the absolute maximum limit is ±10.5V.
The SP503 does require a power-up sequence of
+10V, +5V, -10V for proper operation. Addi-
tional external circuitry will be required for the
correct sequencing. Consult factory for details.
What is the maximum input voltage applied to
the receiver input without damaging the SP503?
The receiver inputs can tolerate up to ±16V in
any protocol without latching up the device.
Since RS-232 ranges from ±5V to ±15V; the
SP503 is well within the accepted range. It may
be worthwhile to include 15V clamping diodes
or transient voltage suppressors so that the re-
ceiver input will be held below ±15V.
What is the maximum short-circuit voltage that
can be applied to a SP503 driver output?
The driver outputs can be shorted up to ±16.0V
without causing damage to the driver. Between
the ±16V range, the SP503 adheres to the RS-
232 short circuit current limit of 100mA and to
the RS-422/RS-423 limit at 150mA. Again,
transient voltage suppressors or clamping diodes
will protect the SP503 if exceeding the ±16V
range is possible.
What is the state of the SP503 drivers and
receivers when the device is addressed with
0000?
The SP503 drivers are in a high impedance(over
1MΩ) tri-state condition when "0000" is ad-
dressed. The receivers are not tri-stated and the
outputs are undefined. This means that they
could be floating to either a high or low level
depending on the previous state of the receiver
input prior to the 0000 addressing change. The
receiver input impedance is at 15kΩ for "0000".
Can the SP503 be programmed for 7 drivers and
7 receivers in RS-423 mode?
The SP503 can be switched to RS-423 mode by
programming TDEC , TDEC , TDEC , TDEC
3
2
1
0
to "1000" for the drivers and RDEC_X to "1000"
for the receivers. However, external supplies
must be used in order to drive RS-423. The
internal charge pump can only support up to
three RS-423 drivers and three RS-423
receivers.
What is the power dissipation in the SP503 and
in which mode does it consume the most power?
The SP503 dissipates approximately 400mW to
1.4W depending on the protocol. RS-485 mode
consumes the most power at 1.4W. For worst
case power dissipation, all seven drivers were
driven with a TTL signal and the outputs were
looped back into the receiver inputs to generate
a TTL output. All drivers and receivers were
active.
MODE
RS-232
RS-422
RS-485
RS-449
EIA-530
V.35
P_D
0.418W
0.970W
1.382W
0.959W
0.959W
1.055W
What is the state of the SP503 drivers and
receivers when the device is addressed with
1111?
The address for "1111" is not used in the SP503.
If the SP503 is programmed for "1111", the
drivers are approximately 1.0V and at a high
impedance (approx. 9MΩ). The receivers are
not tri-stated and the outputs are undefined. All
receiver inputs are at 15kΩ input impedance.
The SP503 can receive a "1111" address while
V is off. The supply current is approximately
CC
50mA (V_CC = +5V) while the address is at
"1111".
In the RS-232 signal assignments for the DB-25
connector, where does the SP503 account for
Test Mode (TM) ?
For most RS-232 applications, the signals com-
monly used are TxD, TxC, RxD, RxC, RTS,
CTS, DSR, SG, DCD, DTR and Frame Ground.
SP503AN
SP503 Application Note
8
© Copyright 2000 Sipex Corporation