MAX3233E-MAX3235E MAXIM [Maxim Integrated Products], MAX3233E-MAX3235E Datasheet - Page 8

• Manufacturer Part Number: MAX3233E-MAX3235E
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 3b. AutoShutdown Plus, INVALID, and READY Timing Diagram
±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors
By connecting FORCEON to INVALID, the device shuts
down when no valid receiver level and no receiver or
transmitter edge is detected for 30sec. It wakes up
when a valid receiver level or receiver or transmitter
edge is detected.
By connecting FORCEON and FORCEOFF to INVALID,
the device shuts down when no valid receiver level is
detected and wakes up when a valid receiver level is
detected.
A system with AutoShutdown Plus may need time to
wake up. Figure 4 shows a circuit that forces the
transmitters on for 100ms, allowing enough time
for another system to realize that the MAX3233E/
Figure 3a. Receiver Positive/Negative Thresholds for INVALID
8
INVALID
OUTPUT
_______________________________________________________________________________________
TRANSMITTER
TRANSMITTER
+2.7
+0.3
RECEIVER
OUTPUTS
-0.3
-2.7
INPUTS
INPUTS
0
V
V
CC
V+
CC
V-
0
0
t
INVL
INDETERMINATE
INDETERMINATE
INVALID HIGH
INVALID HIGH
INVALID LOW
t
INVH
t
AUTOSHDN
t
WU
MAX3235E is awake. If another system outputs valid
RS-232 signal transitions within that time, the RS-232
ports on both systems remain enabled.
If direct software control is desired, use INVALID to
indicate DTR or Ring Indicator signal. Tie FORCEOFF
and FORCEON together to bypass the AutoShutdown
Plus so the line acts like a SHDN input.
As with all Maxim devices, ESD-protection structures are
incorporated on all pins to protect against electrostatic
discharges encountered during handling and assembly.
The driver outputs and receiver inputs have extra pro-
tection 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
Table 2. INVALID Truth Table
PRESENT AT ANY
RECEIVER INPUT
RS-232 SIGNAL
t
AUTOSHDN
Yes
No
Software-Controlled Shutdown
±15kV ESD Protection
t
WU
INVALID OUTPUT
High
Low
}
INVALID
REGION