MAX1480E Datasheet, PDF (9/19 Pages) Maxim Integrated Products – 15kV ESD-Protected, Isolated RS-485/RS-422

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces
___________________________________________________Pin Description (continued)
PIN
MAX1480EA/ MAX1490EA/
MAX1480EC MAX1490EB
NAME
FUNCTION
—
17
Y
Noninverting Driver Output
—
18
Z
Inverting Driver Output
—
19
B
Inverting Receiver Input
—
20
A
Noninverting Receiver Input
21
—
ISO DE IN Isolated Driver-Enable Input. Connect to ISO DE DRV for normal operation.
22
—
ISO DI IN Isolated Driver Input. Connect to ISO DI DRV for normal operation.
23
—
A
Noninverting Driver Output and Noninverting Receiver Input
24
25
26
27, 28
21
—
22
23, 24
ISO RO DRV
B
ISO V_CC1
AC2, AC1
Isolated Receiver-Output Drive. Connect to ISO RO LED through a resistor (see
Table 1 for MAX1480EA/MAX1480EC, Table 2 for MAX1490EA/MAX1490EB).
Inverting Driver Output and Inverting Receiver Input
Isolated Supply Voltage Source
Internal Connections. Leave these pins unconnected.
Note: For DE´ and DI´ pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for MAX1480EA/
MAX1480EC, Figure 2 for MAX1490EA/MAX1490EB).
Detailed Description
The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
are complete, electrically isolated, RS-485/RS-422 data-
communications interface solutions. Transceivers, opto-
couplers, a power driver, and a transformer in one
standard 28-pin DIP package (24-pin package for the
MAX1490EA/MAX1490EB) provide a complete inter-
face. Signals and power are internally transported
across the isolation barrier (Figures 1, 2). Power is
transferred from the logic side (nonisolated side) to the
isolated side of the barrier through a center-tapped
transformer. Signals cross the barrier through high-
speed optocouplers. A single +5V supply on the logic
side powers both sides of the interface. The
MAX1480EA/MAX1480EC offer half-duplex communica-
tions while the MAX1490EA/MAX1490EB feature full-
duplex communication. The functional input/output
relationships are shown in Tables 3 through 6.
The MAX1480EC/MAX1490EB feature reduced-slew-rate
drivers that minimize EMI and reduce reflections caused
by improperly terminated cables, allowing error-free
transmission at data rates up to 160kbps. The
MAX1480EA/MAX1490EA driver slew rate is not limited,
allowing transmission rates up to 2.5Mbps.
The MAX1480EC/MAX1490EB shutdown feature reduces
supply current to as low as 0.2µA by using the SD pin (see
Low-Power Shutdown Mode section).
Drivers are short-circuit current limited and are protect-
ed against excessive power dissipation by thermal
shutdown circuitry that puts the driver outputs into a
high-impedance state. The receiver input has a fail-safe
feature that guarantees a logic-high RO (logic-low RO)
output if the input is open circuit.
On the MAX1480EA/MAX1480EC, the driver outputs are
enabled by bringing DE´ high. Driver-enable time is typi-
cally 1.0µs. Allow time for the devices to be
enabled before sending data (see Typical Operating
Characteristics). When enabled, driver outputs function
as line drivers. Driver outputs are high impedance when
DE´ is low. When outputs are high impedance, they func-
tion as line receivers.
The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
withstand 1260V_RMS (1min) or 1520V_RMS (1s). The logic
inputs can be driven from TTL/CMOS logic with a series
resistor, and the received data output can directly drive
TTL or CMOS-logic families with only a resistive pullup.
Low-Power Shutdown Mode
The SD pin shuts down the oscillator on the internal power
driver. With the primary side in shutdown, no power is
transferred across the isolation barrier. The DI and DE
optocouplers, however, still consume current if the drive
signals on the nonsolated side are low. Therefore, leave
DI´ and DE´ high or floating when in shutdown mode.
Under these conditions, the MAX1480EC/MAX1490EB
supply current is reduced to as low as 0.2µA.
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