MAX13450E_1011 Datasheet, PDF(14/17 Page) Maxim Integrated Products – RS-485 Transceivers with Integrated 100Ω/120Ω Termination Resistors

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RS-485 Transceivers with Integrated

100â¦/120â¦ Termination Resistors

Thermal Shutdown

When the devicesâ temperature goes over +150NC, the

termination resistor turns off, and the transmitter shuts

down while the receiver stays active.

Fail Safe

The MAX13450E guarantee a logic-high receiver output

when the receiver inputs are shorted or open, or when

they are connected to a terminated transmission line with

all drivers disabled. This is done by setting the receiver

input threshold between -50mV and -200mV. If the dif-

ferential receiver input voltage (A - B) is greater than

or equal to -50mV, RO is logic-high. 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

receiverâs differential input voltage is pulled to 0V by the

termination resistor. With the receiver thresholds of the

MAX13450E, this results in RO being logic-high.

The MAX13451E has the same fail-safe receiver behavior

as the MAX13450E when the INV input is low. When the

INV input is high, RO is low under the fail-safe condition.

ESD Protection

As with all Maxim devices, ESD-protection structures

are incorporated on all pins to protect against elec-

trostatic discharges encountered during handling and

assembly. The driver outputs and receiver inputs of the

MAX13450E/MAX13451E have extra protection against

static electricity. The ESD structures withstand high ESD

in all states: normal operation, shutdown, and powered

down. After an ESD event, the MAX13450E/MAX13451E

keep working without latchup or damage.

ESD protection can be tested in various ways. The trans-

mitter outputs and receiver inputs of the MAX13450E/

MAX13451E are characterized for protection to the fol-

lowing limits:

â¢ Q30kV using the Human Body Model

â¢ Q 15kV using the Air Gap Discharge Method specified

in IEC 61000-4-2

â¢ Q 7kV using the Contact Discharge Method specified

in IEC 61000-4-2

ESD Test Conditions

ESD performance depends on a variety of conditions.

Contact Maxim for a reliability report that documents test

setup, test methodology, and test results.

Human Body Model

Figure 11a shows the Human Body Model, and Figure

11b shows the current waveform it generates when dis-

charged into a low impedance. This model consists of a

100pF capacitor charged to the ESD voltage of interest,

which is then discharged into the test device through a

1.5kI resistor.

IEC 61000-4-2

The IEC 61000-4-2 standard covers ESD testing and

performance of finished equipment. However, it does not

specifically refer to integrated circuits. The MAX13450E/

MAX13451E help equipment designs 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 61000-4-2 model. Hence,

the ESD withstand voltage measured to IEC 61000-4-2

is generally lower than that measured using the Human

Body Model. Figure 11c shows the IEC 61000-4-2 model,

and Figure 11d shows the current waveform for the IEC

61000-4-2 ESD Contact Discharge test.

Applications Information

Typical Applications

The MAX13450E transceiver is designed for full-duplex,

bidirectional data communications on point-to-point

or multipoint bus transmission lines (Figure 12). The

MAX13451E transceiver is designed for half-duplex,

bidirectional data communications on point-to-point or

multipoint bus transmission lines (Figure 13).

256 Transceivers on the Bus

The standard RS-485 receiver input impedance is one-

unit load, and the standard driver can drive up to 32-unit

loads. The MAX13450E/MAX13451E have a 1/8-unit load

receiver input impedance, allowing up to 256 transceiv-

ers 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 MAX13450E/MAX13451E feature reduced slew-rate

drivers that minimize EMI and reduce reflections caused

by improperly terminated cables, allowing error-free data

transmission up to 500kbps.

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