MAX3535EEWI-T Maxim Integrated, MAX3535EEWI-T Datasheet - Page 16

• Manufacturer Part Number: MAX3535EEWI-T
• Description: RS-422/RS-485 Interface IC
• Manufacturer: Maxim Integrated

Specifications of MAX3535EEWI-T

• Data Rate: 1136 Kbps
• Operating Supply Voltage: 3 V to 5.5 V
• Supply Current: 5.9 mA
• Operating Temperature Range: 0 C to + 70 C
• Mounting Style: SMD/SMT
• Input Voltage: 0.8 V to 2 V
• Maximum Power Dissipation: 750 mW
• Output Voltage: 0.4 V to 3.7 V
• Product: RS-422/RS-485 Combination

MAX3535E/MXL1535E
MAX3535E/MXL1535E
16
+3V to +5V, 2500V
Transceivers with ±15kV ESD Protection
The MAX3535E/MXL1535E isolated RS-485/RS-422 full-
duplex transceivers provide 2500V
tion between the RS-485/RS-422 isolation side and the
processor or logic side. These devices allow fast,
1000kbps communication across an isolation barrier even
when the common-mode voltages (i.e., the ground poten-
tials) on either side of the barrier are subject to large dif-
ferences. The isolation barrier consists of two parts. The
first part is a capacitive isolation barrier (integrated high-
voltage capacitors) that allows data transmission
between the logic side and the RS-485/RS-422 isolation
side. Data is sampled and encoded before it is transmit-
ted across the isolation barrier introducing sampling jitter
and further delay into the communication system.
The second part of the isolation barrier consists of an
external transformer with the required primary-to-sec-
ondary isolation, allowing the transmission of operating
power from the logic side across the isolation barrier to
the isolation side. Connect the primary of the external
transformer to the MAX3535E/MXL1535E’s 420kHz
transformer driver outputs ST1 and ST2. Since the
MXL1535E and the MAX3535E operate with different
supply-voltage requirements at their respective isolated
and logic sides, different isolation transformers must be
used with each device (see the Transformer Selection
section). The only external components needed to
complete the system are the isolation transformer, two
diodes, and two low-voltage, 10µF decoupling capaci-
tors (see the Typical Application Circuit ).
The MAX3535E/MXL1535E include one differential dri-
ver, one receiver, and internal circuitry to send the RS-
485 signals and logic signals across the isolation barrier
(including the isolation capacitors). The MAX3535E/
MXL1535E receivers are 1/8 unit load, allowing up to 256
devices on a single bus.
The MAX3535E/MXL1535E feature fail-safe circuitry
ensuring the receiver output maintains a logic-high
state when the receiver inputs are open or shorted, or
when connected to a terminated transmission line with
all drivers disabled (see the Fail Safe section).
The MAX3535E/MXL1535E feature driver slew-rate
select that minimizes electromagnetic interference
(EMI) and reduces reflections caused by improperly
terminated cables at data rates below 400kbps. The
Detailed Description
RMS
of galvanic isola-
RMS
Isolated RS-485/RS-422
driver outputs are short-circuit protected for sourcing or
sinking current and have overvoltage protection. Other
features include hot-swap capability, which holds the
driver off if the driver logic signals are floated after
power is applied. The MAX3535E/MXL1535E have
error-detection circuitry that alerts the processor when
there is a fault and disables the driver until the fault is
removed.
The MAX3535E/MXL1535E guarantee a logic-high
receiver output when the receiver inputs are shorted or
open, or when connected to a terminated transmission
line with all drivers disabled. The receiver threshold is
fixed between -10mV and -200mV. If the differential
receiver input voltage (A - B) is greater than or equal to
-10mV, RO1 is logic-high (Table 2). In the case of a ter-
minated bus with all transmitters disabled, the receiv-
er’s differential input voltage is pulled to zero by the
termination. Due to the receiver thresholds of the
MAX3535E/MXL1535E, this results in a logic-high at
RO1 with a 10mV minimum noise margin.
Two mechanisms prevent excessive output current and
power dissipation caused by faults or by bus con-
tention. The first, a foldback current limit on the output
stage, provides immediate protection against short cir-
cuits over the entire common-mode voltage range. The
second, a thermal-shutdown circuit, forces the driver
outputs into a high-impedance state if the die tempera-
ture exceeds +150°C.
RE functions as both an input and an output. As an
input, RE controls the receiver output enable (RO1). As
an output, RE is used to indicate when there are faults
associated with the operation of the part. This dual
functionality is made possible by using an output driver
stage that can easily be overdriven by most logic
gates. When an external gate is not actively driving RE,
it is driven either high using a 100µA internal pullup
current (fault present), or low using a 60µA internal pull-
down current (no fault). When using RE to control the
receiver-enable output function, be sure to drive it
using a gate that has enough sink and source capabili-
ty to overcome the internal drive.
Driver Output Protection
Monitoring Faults on RE
Maxim Integrated
Fail Safe