MAX3229EEBV MAXIM [Maxim Integrated Products], MAX3229EEBV Datasheet - Page 8

• Manufacturer Part Number: MAX3229EEBV
• Manufacturer: MAXIM [Maxim Integrated Products]

±15kV ESD-Protected +2.5V to +5.5V
RS-232 Transceivers in UCSP
Figure 3. AutoShutdown Trip Levels
8
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
RECEIVER
VOLTAGE
OUTPUT
INVALID
_______________________________________________________________________________________
MANAGEMENT
a)
b)
INPUT
POWER-
(V)
(V)
UNIT
Mouse or Another System
+2.7V
+0.3V
V
V
-0.3V
-2.7V
CC
V+
CC
V-
0
0
0
AUTOSHUTDOWN, TRANSMITTERS DISABLED,
TRANSMITTERS ENABLED, INVALID HIGH
TRANSMITTERS ENABLED, INVALID HIGH
MASTER SHDN LINE
1µA SUPPLY CURRENT, INVALID LOW
t
INVL
INDETERMINATE
INDETERMINATE
FORCEOFF
MAX3228E
MAX3229E
0.1µF
FORCEON
1MΩ
t
INVH
INVALID
REGION
t
WU
The MAX3228E/MAX3229E achieve a 1µA supply cur-
rent with Maxim’s AutoShutdown feature, which oper-
ates when FORCEON is low and FORCEOFF is high.
When these devices sense no valid signal levels on all
receiver inputs for 30µs, the on-board charge pump
and drivers are shut off, reducing V
1µA. This occurs if the RS-232 cable is disconnected or
the connected peripheral transmitters are turned off.
The device turns on again when a valid level is applied
to any RS-232 receiver input. As a result, the system
saves power without changes to the existing BIOS or
operating system.
Table 3 and Figure 2c summarize the MAX3228E/
MAX3229E operating modes. FORCEON and FORCE-
OFF override AutoShutdown. When neither control is
asserted, the IC selects between these states automati-
cally, based on receiver input levels. Figures 2a, 2b,
and 3a depict valid and invalid RS-232 receiver levels.
Figures 3a and 3b show the input levels and timing dia-
gram for AutoShutdown operation.
A system with AutoShutdown may need time to wake
up. Figure 4 shows a circuit that forces the transmitters
on for 100ms, allowing enough time for the other sys-
tem to realize that the MAX3228E/MAX3229E are
active. If the other system transmits valid RS-232 sig-
nals within that time, the RS-232 ports on both systems
remain enabled.
When shut down, the device’s charge pumps are off,
V+ is pulled to V
transmitter outputs are high-impedance. The time
required to exit shutdown is typically 100µs (Figure 3b).
In case FORCEON and FORCEOFF are inaccessible,
these pins have 60kΩ (typ) pullup resistors connected to
V
are not connected, the MAX3228E and MAX3229E will
always be active. Pulling these pins to ground will draw
current from the V
ed from the voltage supplied at V
pullup resistor.
Unlike other RS-232 interface devices, where the
receiver outputs swing between 0 and V
Table 2. Power-On Default States
L
FORCEOFF
PIN NAME
FORCEON
(Table 2). Therefore, if FORCEON and FORCEOFF
POWER-ON DEFAULT
L
CC
supply. This current can be calculat-
, V- is pulled to ground, and the
FORCEON and FORCEOFF
High
High
V
L
Logic Supply Input
L
CC
and the 60kΩ (typ)
AutoShutdown
supply current to
Internal pullup
Internal pullup
MECHANISM
CC
, the