ISL41387IRZ Intersil, ISL41387IRZ Datasheet - Page 17

• Manufacturer Part Number: ISL41387IRZ
• Description: IC TXRX DUAL PROTOCAL ESD 40-QFN
• Manufacturer: Intersil
• Type: Transceiverr

Specifications of ISL41387IRZ

• Number Of Drivers/receivers: 2/2
• Protocol: RS422, RS485
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 40-VFQFN, 40-VFQFPN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Note that the loopback mode uses an additional set of
receivers, as shown in “Typical Operating Circuit” on page 6.
These loopback receivers are not standards compliant, so
the loopback mode can’t be used to implement a half-duplex
RS-485 transceiver.
ISL41387 (QFN Package) Special Features
Logic Supply (V
The ISL41387 (QFN) includes a V
inputs (Tx inputs and control pins) and Rx outputs. These
pins interface with “logic” devices such as UARTs, ASICs,
and μcontrollers, and today most of these devices use power
supplies significantly lower than 5V. Thus, a 5V output level
from a 5V powered dual protocol IC might seriously
overdrive and damage the logic device input. Similarly, the
the logic device’s low V
powered dual protocol input. Connecting the V
power supply of the logic device (as shown in Figure 11)
limits the ISL41387’s Rx output V
and reduces the Tx and control input switching points to
values compatible with the logic device output levels.
Tailoring the logic pin input switching points and output levels
to the supply voltage of the UART, ASIC, or μcontroller
eliminates the need for a level shifter/translator between the
two ICs.
FIGURE 11. USING V
GND
GND
V
V
ISL81387
ISL41387
CC
CC
= +5V
= +5V
R
R
D
D
V
L
A
Y
A
Y
L
Pin)
V
V
V
V
IH
IH
OH
OH
OH
L
≥ 2V
= 0.9V
PIN TO ADJUST LOGIC LEVELS
= 5V
= 2V
might not exceed the V
V
V
17
OH
OH
≤ 2V
≤ 2V
OH
L
UART/PROCESSOR
UART/PROCESSOR
pin that powers the logic
to V
R
T
R
T
XD
XD
XD
XD
V
V
CC
CC
L
(see Figure 14),
= +2V
= +2V
DIODE
DIODE
ESD
GND
ESD
GND
L
pin to the
IH
ISL81387, ISL41387
of a 5V
V
switching points may not provide enough noise margin when
V
various V
particular V
The V
shown in Figures 19 and 20. All of the DC V
to inputs with internal pull-up resistors (SPB, SLEW, RXEN)
being driven to the low input state. The worst case I
occurs when all three of the inputs are low (see Figure 19),
due to the I
input pull-up resistor is ~20µA, so the I
by about 40µA (at V
mode disables the SLEW pin pull-up (middle vs top curve).
When all three inputs are driven high, I
to minimize power dissipation drive these inputs high when
unneeded (e.g., SPB isn’t used in RS-232 mode, so drive it
high).
Active Low Rx Enable (RXEN)
In many RS-485 applications, especially half duplex
configurations, users like to accomplish “echo cancellation”
by disabling the corresponding receiver while its driver is
transmitting data. This function is available on the QFN
package via an active low RXEN pin. The active low function
also simplifies direction control, by allowing a single Tx/Rx
direction control line. If the active high RXEN were used,
either two valuable I/O pins would be used for direction
control, or an external inverter is required between DEN and
RXEN. Figure 12 details the advantage of using the RXEN
pin. When using RXEN, ensure that RXEN is tied to GND.
RS-485 Slew Rate Limited Data Rates
The ISL81387, ISL41387 FAST speed option (SLEW = High)
utilizes 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. With the SLEW
pin low, both product types switch to a moderately slew rate
limited output transition targeted for 460kbps (MED) data
rates. The ISL41387 (QFN version) offers an additional, slew
rate limited data rate that is optimized for 115kbps (SLOW),
and is selected when SLEW = 0 and SPB = 0 (see Table 3).
The slew limited edges permit longer unterminated
networks, or longer stubs off terminated busses, and help
L
L
can be anywhere from V
< 1.8V. Table 5 indicates typical V
L
supply current (I
V
1.65V
L
1.8V
2.0V
2.5V
3.3V
TABLE 5. V
L
values so the user can ascertain whether or not a
L
L
(V)
voltage meets his or her needs.
through the pull-up resistors. I
L
IH
= 5V) when the SPB is high and 232
AND V
L
) is typically less than 60µA, as
CC
IL
V
IH
0.79
0.82
0.87
0.99
1.19
down to 1.65V, but the input
vs V
(V)
L
IH
FOR V
L
L
and V
in Figure 19 drops
drops to ~10nA, so
IL
CC
L
through an
IL
current is due
November 21, 2007
= 5V
values for
V
0.50
0.60
0.69
0.86
1.05
IL
L
(V)
current
FN6201.3