SP3070E Datasheet, PDF (15/20 Pages) Exar Corporation – ±15kV ESD-Protected, 3.3V, 1/8 Load, Failsafe RS-485/RS422 Transceivers

DETAILED DESCRIPTION
ESD structures withstand high ESD in all
states: normal operation, shutdown, and
powered down. After an ESD event, the
SP3070E - SP3078E keep working without
latchup or damage.
ESD protection can be tested in various ways.
The transmitter outputs and receiver inputs of
the SP3070E - SP3078E are characterized
for protection to the following limits:
■ ±15kV using the Human Body Model
■ ±8kV using the Contact Discharge method
specified in IEC 1000-4-2
■ ±15kV Airgap
ESD test conditions
ESD performance depends on a variety
of conditions. Contact Exar for a reliability
report that documents test setup, methodol-
ogy and results.
iec 1000-4-2
The IEC 1000-4-2 standard covers ESD
testing and performance of finished equip-
ment. However, it does not specifically refer
to integrated circuits. The SP3070E family of
devices helps you design equipment to meet
IEC 1000-4-2, without the need for additional
ESD-protection components.
The major difference between tests done
using the Human Body Model and IEC
1000-4-2 is higher peak current in IEC
1000-4-2, because series resistance is
lower in the IEC 1000-4-2 model. Hence,
the ESD withstand voltage measured to
EC 1000-4-2 is generally lower than that
measured using the human body model.
The air-gap test involves approaching the
device with a charged probe. The contact-
discharge method connects the probe to the
device before the probe is energized.
256 Transceivers on the bus
The standard RS-485 receiver input imped-
ance is 12kΩ (1 unit load), and the standard
driver can drive up to 32 unit loads. The
SP3070E family of transceivers has a 1/8-
unit load receiver input impedance (96kΩ),
allowing up to 256 transceivers to be con-
nected in parallel on one communication
line. Any combination of these devices as
well as other RS-485 transceivers with a
total of 32 unit loads or fewer can be con-
nected to the line.
reduced emi and reflections
The SP3070E, SP3071E and SP3072E
feature reduced slew-rate drivers that mini-
mize EMI and reduce reflections caused by
improperly terminated cables, allowing error-
free data transmission up to 250kbps. The
SP3073E, SP3074E and SP3075E offer
higher driver output slew-rate limits, allowing
transmit speeds up to 500kbps.
low power shutdown mode
Low-power shutdown mode is initiated by
bringing both RE high and DE low. In shut-
down, the devices typically draw only 50nA
of supply current.
RE and DE can be driven simultaneously;
the parts are guaranteed not to enter shut-
down if RE is high and DE is low for less
than 50ns. If the inputs are in this state for
at least 600ns, the parts are guaranteed to
enter shutdown.
Enable times t_ZH and t_ZL assume the part was
not in a low-power shutdown state. Enable
times t_ZH(SHDN) and t_ZL(SHDN) assume the parts
were shut down. It takes drivers and receivers
longer to become enabled from low-power
shutdown mode t_ZH(SHDN) and t_ZL(SHDN) than from
driver/receiver-disable mode (t_ZH, t_ZL)
machine model
The machine model for ESD tests all pins
using a 200pF storage capacitor and zero
discharge resistance. The objective is to
emulate the stress caused when I/O pins
are contacted by handling equipment during
test and assembly.
driver output protection
Two mechanisms prevent excessive output
current and power dissipation caused by
faults or by bus contention. First, current
limit on the ouput stage, provides immedi-
ate protection against short circuits over the
whole common-mode voltage range.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
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SP3070E-SP3078E_100_061109