Datasheet

Detailed Description
The MAX3293/MAX3294/MAX3295 are low-power trans-
mitters for RS-485/RS-422 communication. The MAX3295
operates at data rates up to 20Mbps, the MAX3294 up
to 2.5Mbps (slew-rate limited), and the MAX3293 up to
250kbps (slew-rate limited). These devices are enabled
using an active-high driver enable (DE) input. When
disabled, outputs enter a high-impedance state, and the
supply current reduces to 1µA.
The MAX3293/MAX3294/MAX3295 have a hot-swap input
structure that prevents disturbance on the differential signal
lines when a circuit board is plugged into a “hot” back-
plane (see the Hot-Swap Capability section). Drivers are
also short-circuit current limited and are protected against
excessive power dissipation by thermal-shutdown circuitry.
Driver
The driver accepts a single-ended, logic-level input
(DI) and translates it to a differential RS-485/RS-422
level output (Y and Z). Driving DE high enables the
driver, while pulling DE low places the driver outputs
(Y and Z) into a high-impedance state (see Table 1).
Low-Power Shutdown
Force DE low to disable the MAX3293/MAX3294/
MAX3295. In shutdown mode, the device consumes a
maximum of 10µA of supply current.
Hot-Swap Capability
Hot-Swap Input
When circuit boards are inserted into a “hot” or pow-
ered backplane, disturbances to the enable can lead
to data errors. Upon initial circuit board insertion, the
processor undergoes its power-up sequence. During
this period, the output drivers are high impedance
and are unable to drive the DE input of the MAX3293/
MAX3294/MAX3295 to a defined logic level. Leakage
currents up to 10µA from the high-impedance out-
put could cause DE to drift to an incorrect logic state.
Additionally, parasitic circuit board capacitance could
cause coupling of V
CC
or GND to DE. These factors could
improperly enable the driver.
The MAX3293/MAX3294/MAX3295 eliminate all above
issues with hot-swap circuitry. When V
CC
rises, an inter-
nal pulldown circuit holds DE low for approximately 10µs.
After the initial power-up sequence, the pulldown circuit
becomes transparent, resetting the hot-swap tolerable
input.
Figure 7. Differential Power-Up Glitch (0.1V/µs)
Figure 6. Simplified Structure of the Driver Enable Input (DE)
X = Don’t care.
Table 1. MAX3293/MAX3294/
MAX3295 (RS-485/RS-422) Transmitting
Function Table
INPUTS OUTPUTS
DE DI Y Z
0 X Shutdown Shutdown
1 0 0 1
1 1 1 0
DIFFERENTIAL POWER-UP GLITCH
(0.1V/µs)
4µs/div
2V/div
V
CC
Y
Z
Y-Z
0V
10mV/div
AC-COUPLED
10mV/div
AC-COUPLED
20mV/div
V
CC
TIMER
TIMER
EN
DE
(HOT SWAP)
10µs
100µA
M1 M2
5.6kΩ
2mA
MAX3293–MAX3295 20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
www.maximintegrated.com
Maxim Integrated │ 8