ISL41334IRZ-T7A Intersil, ISL41334IRZ-T7A Datasheet - Page 19

• Manufacturer Part Number: ISL41334IRZ-T7A
• Description: IC TXRX RS232/485 DL 2PRT 40QFN
• Manufacturer: Intersil

Specifications of ISL41334IRZ-T7A

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

RS-485 Slew Rate Limited Data Rates
The SOIC and SSOP versions of this IC operate with Tx
output transitions optimized for a 20Mbps data rate. These
fast edges may increase EMI and reflection issues, even
though fast transitions aren’t required at the lower data rates
used by many applications. The ISL41334 (QFN version)
solves this problem by offering two additional, slew rate
limited, data rates that are optimized for speeds of 115kbps,
and 460kbps.The slew limited edges permit longer
unterminated networks, or longer stubs off terminated
busses, and help minimize EMI and reflections.
Nevertheless, for the best jitter performance when driving
long cables, the faster speed options may be preferable,
even at lower data rates. The faster output transitions deliver
less variability (jitter) when loaded with the large capacitance
associated with long cables. Figures 43, 44, and 45 detail
the jitter performance of the three speed options while
driving three different cable lengths. The figures show that
under all conditions the faster the edge rate, the better the
jitter performance. Of course, faster transitions require more
attention to ensuring short stub lengths, and quality
terminations, so there are trade-offs to be made. Assuming a
Typical Performance Curves
FIGURE 14. RECEIVER OUTPUT CURRENT vs RECEIVER
FIGURE 16. RS-485, DRIVER OUTPUT CURRENT vs
100
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
0
0
OUTPUT VOLTAGE
DIFFERENTIAL OUTPUT VOLTAGE
DIFFERENTIAL OUTPUT VOLTAGE (V)
1
RECEIVER OUTPUT VOLTAGE (V)
1
V
2
OH
2
19
, +85°C
V
OH
3
3
, +25°C
V
V
OL
V
CC
OL
, +25°C
4
, +85°C
= V
4
L
ISL81334, ISL41334
= 5V, T
5
5
A
= +25°C; Unless Otherwise Specified.
jitter budget of 10%, it is likely better to go with the slow
speed option for data rates of 115kbps or less, to minimize
fast edge effects. Likewise, the medium speed option is a
good choice for data rates between 115kbps and 460kbps.
For higher data rates, or when the absolute best jitter is
required, use the high speed option.
Speed selection is via the SPA and SPB pins (see Table 3),
and the selection pertains to each port programmed for
RS-485 mode.
Evaluation Board
An evaluation board, part number ISL41334EVAL1, is
available to assist in assessing the dual protocol IC’s
performance. The evaluation board contains a QFN
packaged device, but because the same die is used in all
packages, the board is also useful for evaluating the
functionality of the other versions. The board’s design allows
for evaluation of all standard features, plus the QFN specific
features. Refer to the eval board application note for details,
and contact your sales rep for ordering information.
FIGURE 15. RECEIVER HIGH OUTPUT VOLTAGE vs LOGIC
FIGURE 17. RS-485, DRIVER DIFFERENTIAL OUTPUT
3.6
3.5
3.4
3.3
3.2
3.1
3.0
5
4
3
2
1
0
0
-40
SUPPLY VOLTAGE (V
VOLTAGE vs TEMPERATURE
-25
1
TEMPERATURE (°C)
I
OH
0
= -1mA
2
R
V
DIFF
L
(V)
25
L
= 100Ω
)
3
R
I
OH
I
DIFF
OH
50
= -4mA
= -8mA
= 54Ω
4
November 21, 2007
75
FN6202.3
85
5