MAX1481 Datasheet, PDF (12/16 Pages) Maxim Integrated Products – Software-Selectable, Half-/Full-Duplex, Slew-Rate-Limited, 12Mbps, RS-485/RS-422 Transceivers in uMAX Package

Software-Selectable, Half-/Full-Duplex, Slew-Rate-Limited,
12Mbps, RS-485/RS-422 Transceivers in µMAX Package
V_OH
RO
V_OL
1V A
-1V B
1.5V
OUTPUT
1.5V
R_PHL
R_PLH
INPUT
Figure 11. Receiver Propagation Delays
3V
RE
1.5V
0V
V_CC
RO
RO
0V
1.5V
R_ZL(SHDN), R_ZL
R_LZ
1.5V _{OUTPUT NORMALLY LOW}
OUTPUT NORMALLY HIGH
1.5V
R_ZH(SHDN), R_ZH
R_HZ
V_OL + 0.5V
V_OH - 0.5V
Figure 12. Receiver Enable and Disable Times
(MAX1481/MAX1484 only)
B
ATE
V_ID
RR
RECEIVER
OUTPUT
A
20dB/div
Figure 13. Receiver Propagation Delay Test Circuit
Low-Power Shutdown Mode
(MAX1481 only)
Low-power shutdown mode is initiated by bringing both
RE high and DE low. In shutdown, the MAX1481 typi-
cally draws only 0.1µA of supply current.
RE and DE may be driven simultaneously; the parts are
guaranteed not to enter shutdown if RE is high and DE
is low for less than 50ns. If the inputs are in this state
for at least 600ns, the parts are guaranteed to enter
shutdown.
Enable times t__ZH and t__ZL in the Switching Character-
istics tables assume the part was not in low-power shut-
down. Enable times t_ZH_(SHDN) and t_ZL_(SHDN) assume
the parts were shut down. It takes drivers and receivers
0Hz
250kHz/div
2.5MHz
Figure 14. Driver Output Waveform and FFT Plot of
MAX1484/MAX1486 Transmitting a 20kHz signal
longer to become enabled from the low-power shutdown
mode (t__ZH(SHDN), t__ZL(SHDN)) than from the
driver/receiver disable mode (t__ZH, t__ZL).
Driver Output Protection
Excessive output current and power dissipation caused
by faults or by bus contention are prevented by two
mechanisms. A foldback current limit on the output
stage provides immediate protection against short cir-
cuits over the whole common-mode voltage range (see
Typical Operating Characteristics). In addition, a ther-
mal shutdown circuit forces the driver outputs into a
high-impedance state if the die temperature becomes
excessive.
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