required input current. At this time the SR latch resets

and Q1 turns off. When Q1 turns off, EN reverts to a

drops below 1V, the hot-swap input is reset.

The EN12 and EN34 input structures are identical to the

EN input. For the EN input, there is a complimentary cir-

cuit employing two PMOS devices pulling the EN input

Hot-Swap Line Transient

The circuit of Figure 10 shows a typical offset termina-

tion used to guarantee a greater than 200mV offset

when a line is not driven. The 50pF represents the mini-

mum parasitic capacitance which would exist in a typi-

cal application. In most cases, more capacitance exists

in the system and will reduce the magnitude of the

glitch. During a “hot-swap” event when the driver is

connected to the line and is powered up, the driver

must not cause the differential signal to drop below

200mV. Figures 11 and 12 show the results of the

MAX3040–MAX3045 during power-up for two different

the 100

Ω termination, the differential signal across the

termination, and shows the hot-swap line transient

stays above the 200mV RS-485 specification.

Operation of Enable Pins

The MAX3040–MAX3045 family has two enable-func-

tional versions:

The MAX3040/MAX3041/MAX3042B have two transmit-

ter enable inputs EN12 and EN34. EN12 controls the

transmitters 1 and 2, and EN34 controls transmitters 3

and 4. EN12 and EN34 are active-high and the part will

enter the low-power shutdown mode when both are

pulled low. The transmitter outputs are high impedance

when disabled (Table 2).

The MAX3043/MAX3044/MAX3045B have two transmit-

ter enable inputs EN and EN, which are active-high and

active-low, respectively. When EN is logic high or EN is

logic low all transmitters are active. When EN is pulled

low and EN is driven high, all transmitters are disabled

and the part enters the low-power shutdown mode. The

transmitter outputs are high impedance when disabled

(Table 3).

Applications Information

Typical Applications

The MAX3040–MAX3045 offer optimum performance

when used with the MAX3093E/MAX3095 5V quad

receivers or MAX3094E/MAX3096 3V quad differential

line receivers. Figure 13 shows a typical RS-485 con-

nection for transmitting and receiving data and Figure

14 shows a typical multi-point connection.

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

Transmitters

10

______________________________________________________________________________________

TIMER

TIMER

EN

EN

(HOT SWAP)

10

µs

85

µA

Q1

Q2

5.6k

Ω

700

µA

Figure 9. Simplified Structure of the Driver Enable Pin (EN)