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MAX3233ECPP+

P1-P3P4-P6P7-P9P10-P12
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
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/
MAX3235E is awake. If another system outputs valid
RS-232 signal transitions within that time, the RS-232
ports on both systems remain enabled.
Software-Controlled Shutdown
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.
±15kV ESD Protection
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
MAX3233E/MAX3235E
±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors
8 _______________________________________________________________________________________
Table 2. INVALID Truth Table
LowNo
HighYes
INVALID OUTPUT
RS-232 SIGNAL
PRESENT AT ANY
RECEIVER INPUT
RECEIVER INPUT LEVELS (V)
-2.7
-0.3
+2.7
+0.3
0
INDETERMINATE
INVALID HIGH
INVALID LOW
INVALID HIGH
INDETERMINATE
Figure 3a. Receiver Positive/Negative Thresholds for
INVALID
V
CC
0
V+
V-
V
CC
0
INVALID
OUTPUT
TRANSMITTER
INPUTS
RECEIVER
INPUTS
}
INVALID
REGION
TRANSMITTER
OUTPUTS
t
AUTOSHDN
t
WU
t
WU
t
INVL
t
INVH
t
AUTOSHDN
Figure 3b. AutoShutdown Plus,
INVALID,
and READY Timing Diagram
MAX3233E/MAX3235E
±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors
_______________________________________________________________________________________ 9
event, Maxim’s E versions keep working without
latchup, whereas competing RS-232 products can
latch and must be powered down to remove latchup.
ESD protection can be tested in various ways; the
transmitter outputs and receiver inputs of this product
family are characterized for protection to the following
limits:
1) ±15kV using the Human Body Model
2) ±8kV using the Contact Discharge method specified
in IEC 1000-4-2
3) ±15kV using IEC 1000-4-2’s Air-Gap Discharge
method
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, test methodology, and test results.
Human Body Model
Figure 5a shows the Human Body Model and Figure 5b
shows the current waveform it generates when dis-
charged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of inter-
est, which is then discharged into the test device
through a 1.5kΩ resistor.
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and per-
formance of finished equipment; it does not specifically
refer to integrated circuits. The MAX3233E/MAX3235E
help you design equipment that meets Level 4 (the high-
est level) of IEC 1000-4-2, without the need for additional
ESD-protection components.
The major difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak cur-
rent in IEC 1000-4-2, because series resistance is lower
in the IEC 1000-4-2 model. Hence, the ESD withstand
voltage measured to IEC 1000-4-2 is generally lower than
FORCEON
MASTER SHDN LINE
0.1µF1MΩ
FORCEOFF
MAX3233E
MAX3235E
POWER-
MANAGEMENT
UNIT
Figure 4. AutoShutdown Plus Initial Turn-On to Wake Up
Another System
Figure 5b. Human Body Current Waveform
CHARGE-CURRENT
LIMIT RESISTOR
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
C
s
100pF
R
C
1MΩ R
D
1500Ω
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
Figure 5a. Human Body ESD Test Model
Figure 6a. IEC 1000-4-2 ESD Test Model
CHARGE CURRENT
LIMIT RESISTOR
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
C
s
150pF
R
C
50MΩ to 100MΩ R
D
330Ω
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
P1-P3P4-P6P7-P9P10-P12

MAX3233ECPP+

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IC TXRX RS-232 DL 20-DIP
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