Datasheet

MAX3233E/MAX3235E
±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors
_______________________________________________________________________________________ 7
applied to any RS-232 receiver or transmitter input. As a
result, the system saves power without changes to the
existing BIOS or operating system.
Figures 2a and 2b depict invalid and valid RS-232
receiver voltage levels. INVALID indicates the receiver
input’s condition, and is independent of FORCEON and
FORCEOFF states. Figure 2 and Tables 1 and 2 sum-
marize the operating modes. FORCEON and FORCE-
OFF override AutoShutdown Plus circuitry. When nei-
ther control is asserted, the IC selects between these
states automatically based on the last receiver or trans-
mitter input edge received.
When shut down, the device’s charge pumps turn off,
V+ is pulled to V
CC
, V- is pulled to ground, and the
transmitter outputs are high impedance. The time
required to exit shutdown is typically 100µs (Figure 7).
Table 1. Output Control Truth Table
X = Don’t care
*
INVALID connected to FORCEON
**
INVALID connected to FORCEON and FORCEOFF
OPERATION STATUS FORCEON
FORCEOFF
VALID
RECEIVER
LEVEL
Rx or Tx EDGE
WITHIN 30sec
T_OUT R_OUT
Shutdown (Forced Off) X 0 X X High-Z Active
Normal Operation (Forced On) 1 1 X X Active Active
Normal Operation
(AutoShutdown Plus)
0 1 X Yes Active Active
Shutdown
(AutoShutdown Plus)
0 1 X No High-Z Active
Normal Operation
INVALID*
1 Yes X Active Active
Normal Operation
INVALID*
1 X Yes Active Active
Shutdown
INVALID*
1 No No High-Z Active
Normal Operation
(AutoShutdown)
INVALID* INVALID**
Yes X Active Active
Shutdown (AutoShutdown)
INVALID* INVALID**
No X High-Z Active
AUTOSHDN*
R_IN
T_IN
R
S
30sec
TIMER
EDGE
DETECT
EDGE
DETECT
FORCEOFF
FORCEON
*AUTOSHDN IS ONLY AN INTERNAL SIGNAL.
Figure 2c. AutoShutdown Plus Logic
POWERDOWN*
AUTOSHDN
FORCEOFF
FORCEON
POWERDOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL
STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES.
*
Figure 2d. Power-Down Logic