Datasheet

MAX3040–MAX3045
required input current. At this time the SR latch resets
and Q1 turns off. When Q1 turns off, EN reverts to a
standard, high-impedance CMOS input. Whenever V
CC
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
to V
CC
.
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
V
CC
ramp rates (0.1V/µs and 1V/µs). The photos show
the V
CC
ramp, the single-ended signal on each side of
the 100Ω 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 ______________________________________________________________________________________
V
CC
TIMER
TIMER
EN
EN
(HOT SWAP)
10µs
85µA
Q1 Q2
5.6kΩ
700µA
Figure 9. Simplified Structure of the Driver Enable Pin (EN)