ISL32172E Datasheet, PDF (10/20 Pages) Intersil Corporation – QUAD, ±16.5kV ESD Protected, 3.0V to 5.5V, Low Power, RS-422 Transmitters

ISL32172E, ISL32272E, ISL32372E, ISL32174E, ISL32274E, ISL32374E, ISL32179E
Test Circuits and Waveforms (Continued)
EN
V_CC OR V_L
DI
SIGNAL
GENERATOR
Z
D
Y
100Ω
C_D
+
V_OD
-
DI
DIFF OUT (Y - Z)
-V_OD
LOWER OF V_CC OR V_L
0V
+V_{OD 0V}
FIGURE 4A. TEST CIRCUIT
FIGURE 4B. MEASUREMENT POINTS
FIGURE 4. DRIVER DATA RATE
Application Information
RS-422 is a differential (balanced) data transmission
standard for use in long haul or noisy environments. RS-422
is a point-to-multipoint (multidrop) standard, which allows
only one driver and up to 10 (assuming one unit load
devices) receivers on each bus.
Driver Features
These RS-422 drivers are differential output devices that
deliver at least 2V across a 100Ω load. The drivers feature
low propagation delay skew to maximize bit width, and to
minimize EMI.
The 460kbps driver outputs are slew rate limited to minimize
EMI, and to reduce reflections in unterminated or improperly
terminated networks. Outputs of the 10Mbps and 32Mbps
drivers are not limited, so faster output transition times allow
the higher data rates.
Driver Enable Functions
All product types include functionality to allow disabling of
the Tx outputs. The ISL32x72E types feature group (all four
Tx) enable functions that are active high (EN) or active low
(EN). Drivers enable when EN = 1, or when EN = 0, and they
disable only when EN = 0 and EN = 1. ISL32x74E versions
use active high paired enable functions (EN12 and EN34)
that enable (when high) or disable (when low) the
corresponding pairs of Tx. All four of these enable pins have
internal pull-up resistors to V_CC, but unused enable pins that
need to be high (e.g., EN when using the EN input for enable
control, or EN12 and EN34 when using always enabled
drivers) should always be connected externally to V_CC. If
V_CC transients might exceed 7V, then inserting a series
resistor between the input(s) and V_CC limits the current that
will flow if the input’s ESD protection starts conducting.
The ISL32179E has the most flexible enable scheme. Its six
enable pins allow for group, paired, or individual channel
enable control. Figure 5 details the ISL32179E’s internal
enable logic. To utilize a group enable function, connect all
the ENx pins high, and handle the EN and EN pins as
described in the previous paragraph. For paired enables,
connect EN and EN high (for the lowest current in SHDN
mode, if SHDN is used) and tie EN1 and EN2 together, and
EN3 and EN4 together. For individual channel enables,
again connect EN and EN high, and drive the appropriate
ENX (active high) for the particular channel. All of the enable
pins incorporate pull-up resistors to V_CC, but unused enable
pins of any type should be externally connected high, rather
than being left floating. Connecting to V_CC is the best
choice, but V_L may be utilized as long as SHDN power isn’t
a primary concern (for each V_L connected input, I_CC
increases by ((V_CC - V_L)/600kΩ). If V_CC or V_L transients
might exceed 7V, then inserting a series resistor between
the input(s) and the supply limits the current that will flow if
the input’s ESD protection starts conducting.
ENX
1 OF 4 CHANNELS
V_CC ^VCC
EN
CHX EN
EN
V_CC
FIGURE 5. ISL32179E ENABLE LOGIC
Wide Supply Range
These ICs are designed to operate with a wide range of
supply voltages from 3.0V to 5.5V, and they meet the
RS-422 specifications for that full supply voltage range.
5.5V TOLERANT LOGIC PINS
Logic input pins (driver inputs, enables, SHDNEN) contain
no ESD nor parasitic diodes to V_CC (nor to V_L), so they
withstand input voltages exceeding 5.5V regardless of the
V_CC and V_L voltages. Input voltages up to 7V are easily
tolerated.
Logic Supply (V_L Pin, ISL32179E Only)
Note: Power-up V_CC before powering up the V_L supply. If
unused enable pins are connected to V_L rather than to V_CC,
then a small I_CC ((V_CC - V_L)/600kΩ) will flow due to the
internal pull-up resistor connecting to V_CC.
The ISL32179E includes a V_L pin that powers the logic
inputs (driver inputs, enables, SHDNEN). These pins
interface with “logic” devices such as UARTs, ASICs, and
10
FN6824.0
December 16, 2008