±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,
Up to 1Mbps, True RS-232 Transceivers
MAX3222E/MAX3232E/MAX3237E/MAX3241E
†
/MAX3246E
V
CC
5V/div
0
SHDN
T2OUT
V
CC
PROTECTION
DIODE
Rx
PREVIOUS
RS-232
2V/div
0
5kΩ
UART
Tx
GND
SHDN = GND
V
CC
= 3.3V
C1–C4 = 0.1µF
40µs/div
T1OUT
a)
OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM
A ACTIVE RECEIVER OUTPUT IN SHUTDOWN.
V
CC
TO
µP
LOGIC
TRANSITION
DETECTOR
Figure 3. Transmitter Outputs Recovering from Shutdown or
Powering Up
MAX3222E/MAX3237E/MAX3241E/
MAX3246E Shutdown Mode
MAX3237E/MAX3241E
R1OUTB
V
CC
PROTECTION
DIODE
Rx
R1OUT
THREE-STATED
EN = V
CC
5kΩ
R1IN
UART
Tx
GND
T1IN
SHDN = GND
T1OUT
Supply current falls to less than 1µA in shutdown mode
(SHDN = low). The MAX3237E’s supply current falls
to10nA (typ) when all receiver inputs are in the invalid
range (-0.3V < R_IN < +0.3). When shut down, the
device’s charge pumps are shut off, V+ is pulled down
to V
CC
, V- is pulled to ground, and the transmitter out-
puts are disabled (high impedance). The time required
to recover from shutdown is typically 100µs, as shown
in Figure 3. Connect
SHDN
to V
CC
if shutdown mode is
not used.
SHDN
has no effect on R_OUT or R_OUTB
(MAX3237E/MAX3241E).
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated to protect against electrostatic dis-
charges encountered during handling and assembly.
The driver outputs and receiver inputs of the
MAX3222E/MAX3232E/MAX3237E/MAX3241E/MAX3246E
have extra protection against static electricity. Maxim’s
engineers have developed state-of-the-art structures to
protect these pins against ESD of ±15kV without damage.
The ESD structures withstand high ESD in all states:
normal operation, shutdown, and powered down. After
an ESD event, Maxim’s E versions keep working without
latchup, whereas competing RS-232 products can latch
and must be powered down to remove latchup.
Furthermore, the MAX3237E logic I/O pins also have
±15kV ESD protection. Protecting the logic I/O pins to
±15kV makes the MAX3237E ideal for data cable
applications.
9
b)
NEW MAX3237E/MAX3241E: EN SHUTS DOWN RECEIVER OUTPUTS
B (EXCEPT FOR B OUTPUTS), SO NO CURRENT FLOWS TO UART IN SHUTDOWN.
B B OUTPUTS INDICATE RECEIVER ACTIVITY DURING SHUTDOWN WITH EN HIGH.
Figure 2. Detection of RS-232 Activity when the UART and
Interface are Shut Down; Comparison of MAX3237E/MAX3241E
(b) with Previous Transceivers (a)
The complementary outputs on the MAX3237E/
MAX3241E (R_OUTB) are always active, regardless of the
state of
EN
or
SHDN.
This allows the device to be used
for ring indicator applications without forward biasing
other devices connected to the receiver outputs. This is
ideal for systems where V
CC
drops to zero in shutdown
to accommodate peripherals such as UARTs (Figure 2).
_______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
