SP503AN

SP503 Application Note

© Copyright 2000 Sipex Corporation

8

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

The

external voltage should be +10V for V

-10V for V

The tolerance is

±5%. The

absolute minimum limit for the external supplies

is

±7Vandtheabsolutemaximumlimitis±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

1M

Ω) 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 15k

Ω 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

to "1000" for the drivers and RDEC

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

P

D

RS-232

0.418W

RS-422

0.970W

RS-485

1.382W

RS-449

0.959W

EIA-530

0.959W

V.35

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. 9M

Ω). The receivers are

not tri-stated and the outputs are undefined. All

receiver inputs are at 15k

Ω input impedance.

The SP503 can receive a "1111" address while

V

50mA (V

"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.