±10kV ESD-Protected, Quad 5V RS-485/RS-422

Transmitters

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9

IEC 1000-4-4 Burst/Electrical Fast

Transient Test Levels

(For Communication Lines)

The stresses are applied while the MAX3040–MAX3045

are powered up. Test results are reported as:

1) Normal performance within the specification limits.

2) Temporary degradation or loss of function or perfor-

mance which is self-recoverable.

3) Temporary degradation, loss of function or perfor-

mance requiring operator intervention, such as sys-

tem reset.

4) Degradation or loss of function not recoverable due

to damage.

The MAX3040–MAX3045 meets classification 2 listed

above. Additionally, the MAX3040–MAX3045 will not

latchup during the IEC burst stress events.

Hot-Swap Capability

Hot-Swap Inputs

When circuit boards are plugged into a “hot” back-

plane, there can be disturbances to the differential sig-

nal levels that could be detected by receivers

connected to the transmission line. This erroneous data

could cause data errors to an RS-485/RS-422 system.

To avoid this, the MAX3040–MAX3045 have hot-swap

capable inputs.

When a circuit board is plugged into a “hot” backplane

there is an interval during which the processor is going

through its power-up sequence. During this time, the

processor’s output drivers are high impedance and will

be unable to drive the enable inputs of the

MAX3040–MAX3045 (EN, EN, EN_) to defined logic lev-

els. Leakage currents from these high impedance dri-

vers, of as much as 10µA, could cause the enable

inputs of the MAX3040–MAX3045 to drift high or low.

Additionally, parasitic capacitance of the circuit board

could cause capacitive coupling of the enable inputs to

enable inputs of the MAX3040–MAX3045 to drift to lev-

els that may enable the transmitter outputs (Y_ and Z_).

To avoid this problem, the hot-swap input provides a

method of holding the enable inputs of the

ramps up. This hot-swap input is able to overcome the

leakage currents and parasitic capacitances that may

pull the enable inputs to the enabled state.

Hot-Swap Input Circuitry

In the MAX3040–MAX3045 the enable inputs feature

hot-swap capability. At the input there are two NMOS

up from 0, an internal 10µs timer turns on Q2 and sets

the SR latch, which also turns on Q1. Transistors Q2, a

700µA current sink, and Q1, an 85µA current sink, pull

EN to GND through a 5.6k

Ω resistor. Q2 is designed to

pull the EN input to the disabled state against an exter-

nal parasitic capacitance of up to 100pF that is trying to

enable the EN input. After 10µs, the timer turns Q2 off

and Q1 remains on, holding the EN input low against

three-state output leakages that might enable EN. Q1

remains on until an external source overcomes the

U = HIGH-VOLTAGE SOURCE

SPARK GAP

U

50

Ω

COAXIAL

OUTPUT

Figure 7. Simplified Circuit Diagram of a Fast Transient/Burst

Generator

REPETITION PERIOD (DEPENDS ON THE TEST VOLTAGE LEVER,

IN CONFORMITY WITH THE VALUES INDICATED IN 6.1.2).

BURST

BURST DURATION

BURST PERIOD 300ms

PULSE

15ms

Figure 8. General Graph of a Fast Transient Burst