SP3070-3078E Datasheet, PDF (14/19 Pages) Sipex Corporation – 15kV ESD-Protected, 3.3V, 1/8 Load, Failsafe RS-485/RS422 Transceivers

DETAILED DESCRIPTION
The SP307XE family of high speed transceiv-
ers for RS-485/RS-422 communication con-
tain one driver and one receiver. These
devices feature fail-safe circuitry, which guar-
antees a logic-high receiver output when the
receiver inputs are open or shorted, or when
they are connected to a terminated transmis-
sion line with all drivers disabled. The
SP3070E, SP3072E, SP3073E, SP3075E,
SP3076E and SP3078E also feature a
hotswap capability allowing live insertion with-
out error data transfer. The SP3070E,
SP3071E and SP3072E feature reduced slew-
rate drivers that minimize EMI and reduce
reflections caused by improperly terminated
cables, allowing error-free data transmission
up to 250kbps. The SP3073E, SP3074E and
SP3075E also offer slew -rate limits allowing
transmit speeds up to 500kbps. The SP3076E,
SP3077E, SP3078E driver slew rates are not
limited, making transmit speeds up to 16Mbps
possible.
The SP3072E, SP3075E and SP3078E are
half-duplex transceivers, while the SP3070E,
SP3071E, SP3073E, SP3074E, SP3076E,
and SP3077E are full duplex transceivers.
All devices operate from a single 3.3V supply.
Drivers are output short-circuit current limited.
Thermal-shutdown circuitry protects drivers
against excessive power dissipation. When
activated, the thermal-shutdown circuitry
places the driver outputs into a high-imped-
ance state.
RECEIVER INPUT FILTERING
SP3070-SP3075 receivers incorporate input
filtering in addition to input hysteresis. This
filtering enhances noise immunity with differ-
ential signals that have very slow rise and fall
times. Receiver propagation delay increases
by 25% due to this filtering.
FAIL SAFE
The SP3070 family guarantees a logic-high
receiver output when the receiver inputs are
shorted, open, or when they are connected to
a terminated transmission line with all drivers
DETAILED DESCRIPTION
disabled. If A - B is less than or equal to -
200mV, RO is logic low. In the case of a
terminated bus with all transmitters disabled
the receiver's differential input voltage is pulled
to 0V by the termination. With the receiver
thresholds of the SP3070E family, this results
in a logic high with a 50mV minimum noise
margin. In compliance with the EIA/TIA-485
standard, the SP3070E family has a 50mV -
200mV threshold.
HOT-SWAP CAPABILITY
When circuit boards are inserted into a hot
backplane, differential disturbances to the
data bus can lead to data errors. Upon initial
circuit board insertion, the data communica-
tion processor undergoes its own power-up
sequence. During this period, the processor's
logic-output drivers are high impedance and
are unable to drive the DE and RE inputs of
these devices to a defined logic level. Leak-
age currents up to 10µA from the high-imped-
ance state of the processor's logic drivers
could cause standard CMOS enable inputs of
a transceiver to drift to an incorrect logic level.
Additionally, parasitic circuit board capaci-
tance could cause coupling of VCC or GND to
the enable inputs. Without the hot-swap capa-
bility, these factors could improperly enable
the transceiver's driver or receiver.
When VCC rises, an internal pulldown circuit
holds DE low and RE high for approximately
10 microseconds. After the initial power-up
sequence, the pulldown circuit becomes trans-
parent, resetting the hot-swap tolerable input.
15KV ESD PROTECTION
As with all Sipex devices, ESD-protection
structures are incorporated on all pins to
protect against electrostatic discharges en-
countered during handling and assembly. The
driver output and receiver inputs of the
SP3070E family of devices have extra protec-
tion against static electricity. Sipex's engi-
neering team have developed state of the art
structures to protect these pins against ESD
of 15kV without damage. The ESD structures
withstand high ESD in all states: normal op-
Date: 03/28/05
SP3070E - SP3078E Family, ±15kV ESD-Protected, Failsafe RS-485/RS422 Transceivers
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