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MAX3232CSE+ 开发手册 - Maxim Integrated（美信）
制造商:
Maxim Integrated（美信）
分类:
接口芯片
封装:
SOIC-16
描述:
MAXIM INTEGRATED PRODUCTS MAX3232CSE+. 收发器, RS232, 2驱动器, 3V-5.5电源, SOIC-16
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MAX3232CSE+数据手册
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The RS-232 port in most portable systems transmits and receives for only a small percentage of the time
that power is applied; for the rest of the time it may waste power needlessly. An ideal RS-232 transceiver,
therefore, should shut itself down when not transmitting or receiving.
Early RS-232 ICs for portable systems provided a shutdown pin, but the result was complete shutdown
(deep sleep) in which the chip had no way to detect incoming data. So, the next step was to provide
receivers that remained active during shutdown.
The operating system can theoretically shut down an RS-232 port if, after a suitable delay, it sees no
incoming data transitions or status-line changes. But the choice of delay period presents a problem—you
can miss data if you happen to power down just as a data burst begins, and you'll probably miss some of
the data that wakes up the system and initiates power-up. For these reasons, designers seldom go to the
trouble of introducing a monitoring delay by rewriting the BIOS/operating system.
Maxim engineers had the following goals in designing a new RS-232 transceiver:
1. Use power only when transmitting and receiving data.
2. Meet goal #1 with no compromise in performance.
3. Meet goal #1 with no increase in cost.
An obvious approach is to include a timer that shuts down the IC after a desired time interval. But this
thwarts goal #3 by increasing the die area. The better solution is to monitor all incoming data lines for valid
levels of RS-232 signal voltage. All receiver inputs will be near ground, for example, if the RS-232 port is
not connected or if the far-end transceiver is turned off. Either way, the absence of valid signal levels
causes the chip to enter its shutdown mode automatically, reducing the typical no-load supply current to
1µA.
Maxim has recently introduced four devices with automatic shutdown (Table 2). Most include an output
(valid RS-232) that indicates to the system processor whether an active RS-232 port is connected at the
other end of the cable. The MAX3212 goes one step further; it includes a transition-detect circuit whose
latched output, applied as an interrupt, can wake up the system when a change of state occurs on any
incoming line.
Table 2. RS-232 Transceivers with Automatic-Shutdown Circuitry
Device
Supply
Range(V)
No. of Drivers/
Receivers
No-Load Supply Current
(mA typ/max)
No. of Receivers Active in
Standby
MAX3212 2.7 to 3.6 3/5 1/10 5
MAX3218 1.8 to 4.25 2/2 1/10 2
MAX3223 3 to 3.6 2/2 1/10 2
MAX3243 3 to 3.6 3/5 1/10 5
To see the benefits of automatic shutdown, compare the supply currents of Maxim's earlier RS-232
transceivers against those of their auto-shutdown counterparts:
Original Device No-Load I
SUPPLY
(µA max) Auto-Shutdown Device No-Load I
SUPPLY
(µA max)
MAX3222 500 MAX3223 10
MAX3241 1000 MAX3243 10
MAX218 3000 MAX3218 10
MAX212 3000 MAX3212 10
Auto-shutdown devices have FORCE ON/active-low FORCE OFF controls (Figure 2) that can override the
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