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MAX3225ECAP View Datasheet(PDF) - Maxim Integrated

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MAX3225ECAP Datasheet PDF : 21 Pages
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MAX3224E/MAX3225E/
MAX3226E/MAX3227E/MAX3244E/MAX3245E
±15kV ESD-Protected, 1µA, 1Mbps 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
+0.3V
R_IN
30μs
TIMER
INVALID
-0.3V
R
INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST 30μs.
Figure 3a. INVALID Functional Diagram, INVALID Low
T_IN
EDGE
DETECT
R_IN
EDGE
DETECT
FORCEOFF
S
30s
TIMER
R
AUTOSHDN
FORCEON
Figure 3c. AutoShutdown Plus Logic
+2.7V
R_IN
30μs
TIMER
INVALID
-2.7V
R
INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V
FOR LESS THAN 30μs.
Figure 3b. INVALID Functional Diagram, INVALID High
Table 2. INVALID Truth Table
RS-232 SIGNAL
PRESENT AT ANY
RECEIVER INPUT
Yes
No
INVALID OUTPUT
High
Low
peripheral transmitters are turned off, and the UART dri-
ving the transmitter inputs is inactive. The system turns
on again when a valid transition is applied to any
RS-232 receiver or transmitter input. As a result, the sys-
tem saves power without changes to the existing BIOS
or operating system.
Figures 3a and 3b depict valid and invalid RS-232
receiver voltage levels. INVALID indicates the receiver
input’s condition, and is independent of FORCEON and
FORCEOFF states. Figure 3 and Tables 1 and 2 sum-
marize the operating modes of the MAX3224E–
MAX3227E/MAX3244E/MAX3245E. FORCEON and
FORCEOFF override AutoShutdown Plus circuitry.
When neither control is asserted, the IC selects
between these states automatically based on the last
receiver or transmitter input edge received.
FORCEOFF
FORCEON
AUTOSHDN
POWERDOWN*
* POWERDOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
Figure 3d. Power-Down Logic
When shut down, the device’s charge pumps turn off,
V+ is pulled to VCC, V- is pulled to ground, the transmit-
ter outputs are high impedance, and READY
(MAX3224E–MAX3227E) is driven low. The time
required to exit shutdown is typically 100µs (Figure 8).
By connecting FORCEON to INVALID, the MAX3224E–
MAX3227E/MAX3244E/MAX3245E shut down when no
valid receiver level and no receiver or transmitter edge is
detected for 30s, and wake up when a valid receiver
level or receiver or transmitter edge is detected.
+2.7V
+0.3V
0
-0.3V
-2.7V
INVALID HIGH
INDETERMINATE
INVALID LOW
INDETERMINATE
INVALID HIGH
Figure 4a. Receiver Positive/Negative Thresholds for INVALID
Maxim Integrated
11
 

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