參數(shù)資料
型號(hào)： MAX3228-MAX3229
廠商： Maxim Integrated Products, Inc.
英文描述： +2.5V to +5.5V RS-232 Transceivers in UCSP
中文描述： 2.5V至5.5V的RS - 232收發(fā)器的UCSP封裝
文件頁(yè)數(shù)： 8/14頁(yè)
文件大小： 238K
代理商： MAX3228-MAX3229
M
+2.5V to +5.5V RS-232 Transceivers
in UCSP
8
_______________________________________________________________________________________
AutoShutdown
The MAX3228/MAX3229 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 levels on all receiv-
er inputs for 30μs, the on-board charge pump and dri-
vers are shut off, reducing V
CC
supply current to 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 MAX3228/
MAX3229 operating modes. FORCEON and
FORCEOFF
override AutoShutdown. When neither control is assert-
ed, 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 timing 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 sys-
tem to realize that the MAX3228/MAX3229 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 devices
’
charge pumps are off,
V+ is pulled to V
CC
, V- is pulled to ground, and the
transmitter outputs are high-impedance. The time
required to exit shutdown is typically 100μs (Figure 3b).
FORCEON and
FORCEOFF
In case FORCEON and
FORCEOFF
are inaccessible,
these pins have 60
(typ) pullup resistors connected to
V
L
(Table 2). Therefore, if FORCEON and
FORCEOFF
are not connected, the MAX3228 and MAX3229 will
always be active. Pulling these pins to ground will draw
current from the V
L
supply. This current can be calcu-
lated from the voltage supplied at V
L
and the 60k
(typ) pullup resistor.
V
L
Logic Supply Input
Unlike other RS-232 interface devices, where the
receiver outputs swing between 0 and V
CC
, the
Figure 3. AutoShutdown Trip Levels
V-
V
CC
0
V+
0
V
CC
t
INVL
t
WU
INVALID
REGION
RECEIVER
INPUT
VOLTAGE
(V)
INVALID
OUTPUT
(V)
t
INVH
TRANSMITTERS ENABLED, INVALID HIGH
R
AUTOSHUTDOWN, TRANSMITTERS DISABLED,
1
μ
A SUPPLY CURRENT, INVALID LOW
TRANSMITTERS ENABLED, INVALID HIGH
a)
b)
-2.7V
-0.3V
+2.7V
+0.3V
0
INDETERMINATE
INDETERMINATE
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a System
FORCEON
MASTER SHDN LINE
0.1
μ
F
1M
FORCEOFF
MAX3228
MAX3229
POWER-
MANAGEMENT
UNIT
PIN NAME
FORCEON
FORCEOFF
POWER-ON DEFAULT
High
High
MECHANISM
Internal pullup
Internal pullup
Table 2. Power-On Default States
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