M
/
±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,
Up to 1Mbps, True RS-232 Transceivers
10
______________________________________________________________________________________
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).
MAX3222E/MAX3237E/MAX3241E/
MAX3246E Shutdown Mode
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.
T1OUT
R1OUTB
Tx
5k
UART
V
CC
T1IN
LOGIC
TRANSITION
DETECTOR
R1IN
R1OUT
THREE-STATED
EN = V
CC
SHDN = GND
V
CC
TO
μ
P
Rx
PREVIOUS
RS-232
Tx
UART
PROTECTION
DIODE
PROTECTION
DIODE
SHDN = GND
V
CC
V
CC
GND
Rx
5k
a
)
OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM
A
A
ACTIVE RECEIVER OUTPUT IN SHUTDOWN.
b
)
NEW MAX3237E/MAX3241E: EN SHUTS DOWN RECEIVER OUTPUTS
B
B
(EXCEPT FOR B OUTPUTS), SO NO CURRENT FLOWS TO UART IN SHUTDOWN.
B
B
B OUTPUTS INDICATE RECEIVER ACTIVITY DURING SHUTDOWN WITH EN HIGH.
GND
MAX3237E/MAX3241E
Figure 2. Detection of RS-232 Activity when the UART and
Interface are Shut Down; Comparison of MAX3237E/MAX3241E
(b) with Previous Transceivers (a)
40
μ
s/div
SHDN
T2OUT
T1OUT
5V/div
0
2V/div
0
V
CC
= 3.3V
C1–C4 = 0.1
μ
F
Figure 3. Transmitter Outputs Recovering from Shutdown or
Powering Up