ISL3280E Datasheet, PDF (9/15 Pages) Intersil Corporation – ±16.5kV ESD Protected, +125°C, 3.0V to 5.5V, SOT-23/TDFN Packaged, 20Mbps Full Fail-safe, Low Power, RS-485/RS-422 Receivers

ISL3280E, ISL3281E, ISL3282E, ISL3283E, ISL3284E, ISL3285E
All the receivers include a “full fail-safe” function that
guarantees a high level receiver output if the receiver inputs
are unconnected (floating), shorted together, or connected to
a terminated but undriven bus. Fail-safe with shorted inputs is
achieved by setting the Rx upper switching point to -50mV,
thereby ensuring that the Rx sees 0V differential as a high
input level.
All receivers easily support a 20Mbps data rate, and all
receiver outputs (except on the ISL3280E and ISL3284E)
are tri-statable via the active low RE input or by the active
high RE input.
TABLE 2. V_IH, V_IL AND DATA RATE vs V_L FOR V_CC = 3.3V OR
5V
V_L
V_IH
(V)
(V)
V_IL
DATA RATE
(V)
(Mbps)
1.35
0.55
0.5
11
1.6
0.7
0.6
16
1.8
0.8
0.7
23
2.3
1
0.9
27
2.7
1.1
1
30
3.3
1.3
1.2
30
5.5 (i.e., V_CC)
2
1.8
24
V_CC = +3.3V
V_CC = +2V
RO ^{VOH = 3.3V}
R_XD
ESD
DIODE
GND
RE ^{VIH ≥ 2V}
RXEN
V_OH ≤ 2V
GND
ISL3283E
V_CC = +3.3V TO 5V
UART/PROCESSOR
V_CC = +2V
V_L
RO ^{VOH = 2V}
R_XD
ESD
DIODE
GND
V_IH = 1V
RE
RXEN
V_OH ≤ 2V
GND
ISL3282E
UART/PROCESSOR
FIGURE 3. USING V_L PIN TO ADJUST LOGIC LEVELS
Wide Supply Range
The ISL3280E, ISL3281E, ISL3282E, ISL3283E,
ISL3284E, ISL3285E are designed to operate with a wide
range of supply voltages from 3.0V to 5.5V. These devices
meet the RS-422 and RS-485 specifications over this full
range.
Logic Supply (V_L Pin, ISL3282E, ISL3284E,
ISL3285E Only)
Note: Power-up V_CC before powering up the V_L supply.
The ISL3282E, ISL3284E, and ISL3285E include a V_L pin
that powers the logic input (RE or RE) and / or the Rx output.
These pins interface with “logic” devices such as UARTs,
ASICs, and microcontrollers and today most of these
devices use power supplies significantly lower than 3.3V.
Thus, a 3.3V output level from a 3.3V powered RS-485 IC
might seriously overdrive and damage the logic device input.
Similarly, the logic device’s low V_OH might not exceed the
V_IH of a 3.3V or 5V powered RE input. Connecting the V_L
pin to the power supply of the logic device (as shown in
Figure 3) limits the ISL3282E, ISL3284E, ISL3285E’s Rx
output V_OH to V_L (see Figures 6 through 10), and reduces
the RE / RE input switching point to a value compatible with
the logic device’s output levels. Tailoring the logic pin input
switching point and output levels to the supply voltage of the
UART, ASIC, or microcontroller eliminates the need for a
level shifter/translator between the two ICs.
V_L can be anywhere from V_CC down to 1.35V, but the input
switching points may not provide enough noise margin when
V_L < 1.6V. Table 2 indicates typical V_IH, V_IL, and data rate
values for various V_L settings so the user can ascertain
whether or not a particular V_L voltage meets his/her needs.
The quiescent, RO unloaded, V_L supply current (I_L) is
typically less than 60µA for V_L ≤ 3.3V, as shown in Figure 5.
ESD Protection
All pins on these devices include class 3 (>4kV) Human
Body Model (HBM) ESD protection structures, but the
RS-485 pins (receiver inputs) incorporate advanced
structures allowing them to survive ESD events in excess
of ±16.5kV HBM and ±16.5kV IEC61000. The RS-485 pins
are particularly vulnerable to ESD damage because they
typically connect to an exposed port on the exterior of the
finished product. Simply touching the port pins, or
connecting a cable, can cause an ESD event that might
destroy unprotected ICs. These new ESD structures
protect the device whether or not it is powered up, and
without degrading the RS-485 common mode range of -7V
to +12V. This built-in ESD protection eliminates the need
for board level protection structures (e.g., transient
suppression diodes), and the associated, undesirable
capacitive load they present.
9
FN6543.2
October 18, 2007