MAX3226 MAXIM [Maxim Integrated Products], MAX3226 Datasheet - Page 10

• Manufacturer Part Number: MAX3226
• Description: 1uA Supply Current, 1Mbps, 3.0V to 5.5V, RS-232 Transceivers with AutoShutdown Plus
• Manufacturer: MAXIM [Maxim Integrated Products]

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 MAX3224–
MAX3227/MAX3244/MAX3245 devices. 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.
When shut down, the device’s charge pumps turn off,
V+ is pulled to V
ter outputs are high impedance, and READY
(MAX3224–MAX3227) is driven low. The time required
to exit shutdown is typically 100µs (Figure 8).
1µA Supply Current, 1Mbps, 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
Figure 3a. INVALID Functional Diagram, INVALID Low
Figure 3b. INVALID Functional Diagram, INVALID High
Table 2. INVALID Truth Table
10
+0.3V
-0.3V
+2.7V
R_IN
-2.7V
R_IN
INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V
FOR LESS THAN 30 s.
INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST 30 s.
______________________________________________________________________________________
PRESENT AT ANY
RECEIVER INPUT
RS-232 SIGNAL
Yes
No
CC
, V- is pulled to ground, the transmit-
INVALID OUTPUT
TIMER
TIMER
30µs
30µs
R
R
High
Low
INVALID
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.
By connecting FORCEON and FORCEOFF to INVALID,
the MAX3224–MAX3227/MAX3244/MAX3245 shutdown
when no valid receiver level is detected and wake up
Figure 3c. AutoShutdown Plus Logic
Figure 3d. Power-Down Logic
Figure 4a. Receiver Positive/Negative Thresholds for INVALID
* POWERDOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
R_IN
T_IN
AUTOSHDN
FORCEOFF
+2.7V
+0.3V
-0.3V
-2.7V
FORCEON
DETECT
DETECT
0
EDGE
EDGE
FORCEON
INDETERMINATE
INDETERMINATE
INVALID HIGH
INVALID HIGH
INVALID LOW
FORCEOFF
TIMER
30sec
S
R
POWERDOWN*
AUTOSHDN