Rainbow Electronics MAX3079E - Manual (Page 16)

MAX3070E–MAX3079E
MAX3079E Programming
The MAX3079E has several programmable operating
modes. Transmitter rise and fall times are programma-
ble, resulting in maximum data rates of 250kbps,
500kbps, and 16Mbps. To select the desired data rate,
drive SRL to one of three possible states by using a
three-state driver: V
CC , GND, or unconnected. For
250kbps operation, set the three-state device in high-
impedance mode or leave SRL unconnected. For
500kbps operation, drive SRL high or connect it to V
CC .
For 16Mbps operation, drive SRL low or connect it to
GND. SRL can be changed during operation without
interrupting data communications.
Occasionally, twisted-pair lines are connected backward
from normal orientation. The MAX3079E has two pins that
invert the phase of the driver and the receiver to correct
this problem. For normal operation, drive TXP and RXP
low, connect them to ground, or leave them unconnect-
ed (internal pulldown). To invert the driver phase, drive
TXP high or connect it to V
CC
. To invert the receiver
phase, drive RXP high or connect it to V CC . Note that the
receiver threshold is positive when RXP is high.
The MAX3079E can operate in full- or half-duplex
mode. Drive the H/F pin low, leave it unconnected
(internal pulldown), or connect it to GND for full-duplex
operation. Drive H/F high for half-duplex operation. In
full-duplex mode, the pin configuration of the driver and
receiver is the same as that of a MAX3070E. In half-
duplex mode, the receiver inputs are switched to the
driver outputs, connecting outputs Y and Z to inputs A
and B, respectively. In half-duplex mode, the internal
full-duplex receiver input resistors are still connected to
pins 11 and 12.
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electro-
static discharges encountered during handling and
assembly. The driver outputs and receiver inputs of the
MAX3070E family of devices have extra protection
against static electricity. Maxim’s engineers have devel-
oped state-of-the-art structures to protect these pins
against ESD of ±15kV without damage. The ESD struc-
tures withstand high ESD in all states: normal operation,
shutdown, and powered down. After an ESD event, the
MAX3070E–MAX3079E keep working without latchup or
damage.
ESD protection can be tested in various ways. The
transmitter outputs and receiver inputs of the
MAX3070E–MAX3079E are characterized for protection
to the following limits:
• ±15kV using the Human Body Model
• ±6kV using the Contact Discharge method specified
in IEC 1000-4-2
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 10a shows the Human Body Model, and Figure
10b 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
1.5k
Ω resistor.
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and
performance of finished equipment. However, it does
not specifically refer to integrated circuits. The
MAX3070E family of devices helps you design equip-
ment to meet IEC 1000-4-2, without the need for addi-
tional ESD-protection components.
The major difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak
+3.3V, ±15kV ESD-Protected, Fail-Safe,
Hot-Swap, RS-485/RS-422 Transceivers
16 ______________________________________________________________________________________
DE
DE
(HOT SWAP)
5k Ω
TIMER
TIMER
V CC
10 µs
M2 M1
500 µA
100 µA
SR LATCH
Figure 9. Simplified Structure of the Driver Enable Pin (DE)