SP335E
18
RS-232/RS-485/RS-422 TRANSCEIVER WITH INTERNAL TERMINATION REV. 1.0.0
PRODUCT SUMMARY
The SP335 is an advanced multiprotocol transceiver supporting RS-232, RS-485, and RS-422 serial
standards. Integrated cable termination and multiple configuration modes allow all three protocols to be used
interchangeably over a single cable or connector with no additional switching components. Full operation
requires only four external charge pump capacitors.
INTERNALLY SWITCHED CABLE TERMINATION
Enabling and disabling the RS-485/422 termination resistor is one of the largest challenges system designers
face when sharing a single connector or pair of lines across multiple serial protocols. A termination resistor
may be necessary for accurate RS-485/422 communication, but must be removed when the lines are used for
RS-232. SP335 provides an elegant solution to this problem by integrating the termination resistor and
switching control, and allowing it to be switched in and out of the circuit with a single pin. No external switching
components are required. Termination on the receiver inputs will be enabled if both TERM and RS-485/
RS-232
are high.
ENHANCED FAILSAFE
The enhanced failsafe feature of the SP335 guarantees a logic-high receiver output when the receiver inputs
are open, shorted, or terminated but idle/undriven. The enhanced failsafe interprets 0V differential as a logic
high with a minimum 50mV noise margin, while maintaining compliance with the EIA/TIA-485 standard of
±200mV. No external biasing resistors are required, further easing the usage of multiple protocols over a single
connector.
±15kV ESD PROTECTION
ESD protection structures are incorporated on all pins to protect against electrostatic discharges encountered
during handling and assembly. The bus pins (driver outputs and receiver inputs) have extra protection
structures, which have been tested up to ±15kV without damage. These structures withstand high ESD in all
states: normal operation, in shutdown, and when powered off.
ESD protection is be tested in various ways. Exar uses the following methods to qualify the protection
structures designed into SP335:
±8kV using IEC 61000-4-2 Contact Discharge
±15kV using IEC 61000-4-2 Airgap Discharge
±15kV using the Human Body Model (HBM)
The IEC 61000-4-2 standard is more rigorous than HBM, resulting in lower voltage levels compared with HBM
for the same level of ESD protection. Because IEC 61000-4-2 specifies a lower series resistance, the peak
current is higher than HBM. The SP335 has passed both HBM and IEC 61000-4-2 testing without damage.
VARIABLE LOGIC LEVEL VOLTAGE
The SP335 includes a V
L
pin, which reduces the logic level thresholds to interface with processors operating at
reduced supply voltages. This pin should be connected to the supply voltage of the processor, or can be
connected to V
CC
for typical logic levels.
