1 µA S u p p ly Cu rre n t , 1 Mb p s , 3 .0 V t o 5 .5 V,
RS -2 3 2 Tra n s c e ive rs w it h Au t o S h u t d o w n P lu s
EDGE
DETECT
+0.3V
T_IN
FORCEOFF
S
R_IN
AUTOSHDN
30sec
TIMER
30µs
TIMER
R
EDGE
DETECT
INVALID
R_IN
R
-0.3V
INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST 30µs.
FORCEON
Figure 3a. INVALID Functional Diagram, INVALID Low
Figure 3c. AutoShutdown Plus Logic
+2.7V
FORCEOFF
POWERDOWN*
FORCEON
R_IN
30µs
TIMER
R
AUTOSHDN
INVALID
-2.7V
* POWERDOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V
FOR LESS THAN 30µs.
Figure 3d. Power-Down Logic
Figure 3b. INVALID Functional Diagram, INVALID High
Table 2. INVALID Truth Table
INVALID HIGH
RS-232 SIGNAL
PRESENT AT ANY
RECEIVER INPUT
+2.7V
INVALID OUTPUT
INDETERMINATE
Yes
No
High
Low
+0.3V
0
INVALID LOW
INDETERMINATE
INVALID HIGH
-0.3V
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-
ma rize the op e ra ting mod e s of the MAX3224–
MAX3227/MAX3244/MAX3245 devices. FORCEON and
FORCEOFF ove rrid e AutoShutd own Plus c irc uitry.
Whe n ne ithe r c ontrol is a s s e rte d , the IC s e le c ts
between these states automatically based on the last
receiver or transmitter input edge received.
-2.7V
–7/MAX3245
Figure 4a. Receiver Positive/Negative Thresholds for INVALID
By connecting FORCEON to INVALID, the MAX3224–
MAX3227/MAX3244/MAX3245 shut down when no valid
receiver level and no receiver or transmitter edge is
detected for 30sec, and wake up when a valid receiver
level or receiver or transmitter edge is detected.
When shut down, the device’s charge pumps turn off,
V+ is pulled to V , V- is pulled to ground, the transmit-
CC
te r outp uts a re hig h imp e d a nc e , a nd READY
(MAX3224–MAX3227) is driven low. The time required
to exit shutdown is typically 100µs (Figure 8).
By connecting FORCEON and FORCEOFF to INVALID,
the MAX3224–MAX3227/MAX3244/MAX3245 shutdown
when no valid receiver level is detected and wake up
10 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
