MAX3248EEAI-T Maxim Integrated, MAX3248EEAI-T Datasheet - Page 8

• Manufacturer Part Number: MAX3248EEAI-T
• Description: RS-232 Interface IC
• Manufacturer: Maxim Integrated
• Series: MAX3238E, MAX3248Er

Tables 1 and 2 and Figure 3 summarize the MAX3238E/
MAX2348Es’ operating modes. FORCEON and FORCE-
OFF override the automatic circuitry and force the
transceiver into its normal operating state or into its low-
power standby state. When neither control is asserted,
the IC enters AutoShutdown Plus mode and selects
between these states automatically, based on the last
receiver or transmitter input edge received.
When shut down, the devices’ charge pumps turn off,
V+ decays to V
mitter outputs are disabled (high impedance). The time
required to recover from shutdown is typically 25µs
(Figure 4b).
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 feature so the line acts like a SHDN input.
As with all Maxim devices, ESD protection structures
are incorporated to protect against electrostatic dis-
charges (ESDs) encountered during handling and
assembly. The MAX3238E/MAX3248E RS-232 transmit-
ters and receivers, as well as the I/O have extra protec-
tion against static electricity found in normal operation.
Maxim’s engineers developed state-of-the-art struc-
tures to protect these pins against ESD of ±15kV with-
out damage. After an ESD event, the MAX3238E/
MAX3248E keep working without latchup.
ESD protection can be tested in various ways. The pins
are characterized for protection to ±15kV and ±8kV
(see Electrical Characteristics).
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
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-
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
Table 2. INVALID Truth Table
8
RS-232 SIGNAL PRESENT AT
_______________________________________________________________________________________
ANY RECEIVER INPUT
Yes
No
CC,
Software-Controlled Shutdown
V- decays to ground, and the trans-
ESD Test Conditions
Human Body Model
INVALID OUTPUT
ESD Protection
H
L
Figure 3a. INVALID Functional Diagram, INVALID Low
Figure 3b. INVALID Functional Diagram, INVALID High
Figure 3c. AutoShutdown Plus Logic
Figure 3d. Power-Down Logic
+2.7V
+0.3V
-0.3V
-2.7V
R_IN
R_IN
INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V
FOR LESS THAN 60µs.
INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST 60µs.
* POWER DOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
R_IN
T_IN
AUTOSHDN
FORCEOFF
FORCEON
DETECT
DETECT
EDGE
EDGE
FORCEON
FORCEOFF
30s TIMER
TIMER
TIMER
60µs
60µs
S
R
R
R
POWERDOWN*
INVALID
INVALID
AUTOSHDN