MAX3228AE MAXIM [Maxim Integrated Products], MAX3228AE Datasheet - Page 8

• Manufacturer Part Number: MAX3228AE
• Manufacturer: MAXIM [Maxim Integrated Products]

±15kV ESD-Protected +2.5V to +5.5V
RS-232 Transceivers in UCSP and WLP
Figure 3. AutoShutdown Trip Levels
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
8
RECEIVER
VOLTAGE
OUTPUT
INVALID
MANAGEMENT
_______________________________________________________________________________________
a)
b)
INPUT
POWER-
(V)
(V)
UNIT
+2.7V
+0.3V
V
V
Mouse or Another System
-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/AE
MAX3229E/AE
0.1μF
FORCEON
1MΩ
t
INVH
INVALID
REGION
t
WU
The MAX3228E/AE and MAX3229E/AE achieve a 1µA
supply current with Maxim’s AutoShutdown feature,
which operates when FORCEON is low and FORCEOFF
is high. When these devices sense no valid signal lev-
els on all receiver inputs for 30µs, the on-board charge
pump and drivers are shut off, reducing V
current to 1µA. This occurs if the RS-232 cable is dis-
connected 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/AE
and MAX3229E/AE operating modes. FORCEON and
FORCEOFF override AutoShutdown. When neither con-
trol is asserted, the IC selects between these states
automatically, 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 tim-
ing diagram 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
system to realize that the MAX3228E/AE and
MAX3229E/AE are active. If the other system transmits
valid RS-232 signals 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
not connected, the MAX3228E/AE and MAX3229E/AE
will always be active. Pulling these pins to ground will
draw current from the V
culated from the voltage supplied at V
(typ) 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
(Table 2). Therefore, if FORCEON and FORCEOFF are
PIN NAME
FORCEON
POWER-ON DEFAULT
CC
, V- is pulled to ground, and the
FORCEON and FORCEOFF
L
supply. This current can be cal-
High
High
V
L
Logic Supply Input
AutoShutdown
Internal pullup
Internal pullup
L
MECHANISM
and the 60kΩ
CC
CC
supply
, the