■ Industrial Control, Utility Meters Building Automation, Instrumentation, Point of Sale
The SP3070E-3078E differential line transceivers are suitable for bidirectional communication
on balanced multipoint bus transmission lines and comply with both RS485 and RS422 EIA
Standards. Each device consists of a differential driver and differential receiver. All devices
operate from a 3.3V power supply.
High receiver input impedance allows a large number of transceivers to share a common
data bus while maintaining signal margin and without excessive loading or use of expensive
repeaters. The high impedance driver output is maintained over the entire common-mode
voltage range from -7 to +12V. Receivers will failsafe to logic 1 output when inputs are open,
shorted or terminated. Drivers include built-in short-circuit protection and a thermal-overload
shutdown to protect against excessive power dissipation from bus contention or cable faults.
All RS485 receiver inputs and driver outputs are ESD protected up to ±15kV (Air-Gap and
Human Body Model) and up to ±8kV Contact discharge (IEC 61000-4-2). The SP3070ESP3078E devices may not achieve optimal transmit performance if the connected receiver
includes a biasing network to 5.0V without a termination resistor. Please see Exar Application
Note ANI#21 for further details.
-50mV, RO is High. If (A – B) - 200mV, RO is low.
3-2RE
Receiver Output Enable. When RE is low, RO is enabled.
When RE is high, RO is high impedance. RE should be
high and DE low to enter shutdown mode. RE is a hotswap input.
4-3DE
Driver Output Enable. When DE is high, outputs are
enabled. When DE is low, outputs are high impedance. DE
should be low and RE high to enter shutdown mode. DE is
a hot-swap input.
534DI
Driver Input. With DE high, a low level on DI forces
noninverting output low and inverting output high. Similarly,
a high level on DI forces noninverting output high and
inverting output low.
6, 745GNDGround
95-YNoninverting Driver Output
106-ZInverting Driver Output
117-BInverting Receiver Input
--7BInverting Receiver Input and Inverting Driver Output
128-ANoninverting Receiver Input
--6A
Noninverting Receiver Input and Noninverting Driver
Output
1418V
CC
Positive Supply VCC. Bypass VCC to GND with a 0.1uF
capacitor.
The SP307XE family of high speed transceivers for RS-485/RS-422 communication
contain one driver and one receiver. These
devices feature fail-safe circuitry, which
guarantees a logic-high receiver output when
the receiver inputs are open or shorted, or
when they are connected to a terminated
transmission line with all drivers disabled. The
SP3070E, SP3072E, SP3073E, SP3075E,
SP3076E and SP3078E also feature a
hotswap capability allowing live insertion
without error data transfer. The SP3070E,
SP3071E and SP3072E feature reduced
slew-rate drivers that minimize EMI and
reduce reections 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-impedance state.
RECEIVER INPUT FILTERING
SP3070E-SP3075E receivers incorporate
input ltering in addition to input hysteresis.
This ltering enhances noise immunity with
differential signals that have very slow rise
and fall times. Receiver propagation delay
increases by 25% due to this ltering.
FAIL SAFE
The SP3070E 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 disabled. If A - B is less than or equal
DETAILED DESCRIPTION
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 ZeroV 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 communication 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 dened logic level.
Leakage currents up to 10µA from the highimpedance 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 capacitance could cause coupling of
VCC or GND to the enable inputs. Without
the hot-swap capability, 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
transparent, resetting the hot-swap tolerable input.
15KV ESD PROTECTION
As with all Exar devices, ESD-protection
structures are incorporated on all pins to
protect against electrostatic discharges
encountered during handling and assembly.
The driver output and receiver inputs of
the SP3070E family of devices have extra
protection against static electricity. Exar's
engineering 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 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
specied in IEC 61000-4-2
■ ±15kV Airgap
ESD TEST CONDITIONS
ESD performance depends on a variety
of conditions. Contact Exar for a reliability
report that documents test setup, methodology and results.
IEC 61000-4-2
The IEC 61000-4-2 standard covers ESD
testing and performance of nished equipment. However, it does not specically refer
to integrated circuits. The SP3070E family
of devices helps you design equipment to
meet IEC 61000-4-2, without the need for
additional ESD-protection components.
The major difference between tests done
using the Human Body Model and IEC
61000-4-2 is higher peak current in IEC
61000-4-2, because series resistance is
lower in the IEC 1000-4-2 model. Hence,
the ESD withstand voltage measured to
EC 61000-4-2 is generally lower than that
measured using the human body model.
The air-gap test involves approaching the
device with a charged probe. The contactdischarge 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 connected 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 connected to the line.
REDUCED EMI AND REFLECTIONS
The SP3070E, SP3071E and SP3072E
feature reduced slew-rate drivers that mini-
mize EMI and reduce reections 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 shutdown, the devices typically draw only 50nA
of supply current.
RE and DE can be driven simultaneously;
the parts are guaranteed not to enter shutdown 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 tZH and tZL assume the part was
not in a low-power shutdown state. Enable
times t
were shut down. It takes drivers and receivers
ZH(SHDN)
and t
assume the parts
ZL(SHDN)
longer to become enabled from low-power
shutdown mode t
driver/receiver-disable mode (tZH, tZL)
ZH(SHDN)
and t
ZL(SHDN)
than from
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.
Two mechanisms prevent excessive output
current and power dissipation caused by
faults or by bus contention. First, current
limit on the ouput stage, provides immediate protection against short circuits over the
whole common-mode voltage range.
15
Page 16
Second, a thermal-shutdown circuit, forces
PART
NUMBER
Half/Full
Duplex
Datarate
Mbps
Shutdown
Receiver
Driver Enable
Trans.
On Bus
Pin
Count
Industry Standard
Pinout
Pin
Compatible
Upgrade from:
SP3070EFull0.25YesYes25614MAX3070E, 75180
SP3071EFull0.25NoNo2568MAX 3071E, 75179SP3493
SP3072EHalf0.25YesYes2568MAX 3072E, 75176SP3483
SP3073EFull0.5YesYes25614MAX 3073E, 75180
SP3074EFull0.5NoNo2568MAX 3074E, 75179
SP3075EHalf0.5YesYes2568MAX 3075E, 75176SP3494
SP3076EFull16YesYes25614MAX 3076E, 75180SP3491
SP3077EFull16NoNo2568MAX3077E, 75179SP3490
SP3078EHalf16YesYes
2568
MAX 3078E, 75176SP3485,
SP3481
the driver outputs into a high-impedance
state if the die temperature becomes excessive.
LINE LENGTH
The RS-485/RS422 standard covers line
lengths up to 4000ft.
TYPICAL APPLICATIONS
The SP3072E, SP3075E and SP3078E
transceivers are designed for bidirectional
data communications on multipoint bus
transmission lines.
DETAILED DESCRIPTION
To minimize reections, terminate the line at
both ends in its characteristic impedance,
and keep stub lengths off the main line as
short as possible. The slew-rate-limited
SP3070E - SP3075E are more tolerant of
imperfect termination.
06/10/091.0.0Convert to Exar format, update ordering information, correct
subscript on pages 5-7 and change revision to 1.0.0
09/30/101.0.1Correct type error on page 7 on driver switching character-
istics table. Change SP3076E,3077E and 3078E Receiver
enable time from shutdown from 1800ns to 3000ns.
12/02/101.0.2Add reference to Application Note ANI#21 and change ESD
protection levels to IEC 61000-4-2.
Notice
EXAR Corporation reserves the right to make changes to any products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no representation that the circuits are free of patent infringement. Charts and schedules contained herein are
only for illustration purposes and may vary depending upon a user's specic application. While the information in this publication has been carefully
checked;
no responsibility, however, is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can
reasonably be expected to cause failure of the life support system or to signicantly affect its safety or effectiveness. Products are not authorized for
use in such applications unless EXAR Corporation receives, in writting, assurances to its satisfaction that: (a) the risk of injury or damage has been
minimized ; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances.
Copyright 2010 EXAR Corporation
Datasheet December 2010
For technical support please email Exar's Serial Technical Support group at: [email protected]
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.