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參數(shù)資料
| 型號(hào)： | MAX221ECAE+T |
| 廠商： | Maxim Integrated Products |
| 文件頁(yè)數(shù)： | 5/8頁(yè) |
| 文件大?。?/td> | 0K |
| 描述： | IC TXRX RS-232 5V 16-SSOP |
| 產(chǎn)品培訓(xùn)模塊： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 標(biāo)準(zhǔn)包裝： | 2,000 |
| 類(lèi)型： | 收發(fā)器 |
| 驅(qū)動(dòng)器/接收器數(shù)： | 1/1 |
| 規(guī)程： | RS232 |
| 電源電壓： | 4.5 V ~ 5.5 V |
| 安裝類(lèi)型： | 表面貼裝 |
| 封裝/外殼： | 16-SSOP（0.209"，5.30mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 16-SSOP |
| 包裝： | 帶卷 (TR) |
MAX221
+5V, 1A, Single RS-232 Transceiver
with AutoShutdown
_______________________________________________________________________________________
5
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX221’s internal power supply consists of a dual
charge pump that provides a positive output voltage
(doubling charge pump) and a negative voltage (invert-
ing charge pump) from a single +5V supply. The
charge pumps operate in continuous mode. Each
charge pump requires a flying capacitor (C1, C2) and a
reservoir capacitor (C3, C4) to generate the V+ and V-
supplies.
RS-232 Transmitter
The transmitter is an inverting level translator that con-
verts CMOS-logic levels to 5.0V EIA/TIA-232 levels. It
guarantees a 250kbps data rate with worst-case loads
of 3k
in parallel with 1000pF.
When FORCEOFF is driven to ground, or when the
AutoShutdown circuitry senses invalid voltage levels on
the receiver input, the transmitter is disabled and the out-
put is forced into a high-impedance state. The transmitter
input does not have a pull-up resistor.
RS-232 Receiver
The MAX221’s receiver converts RS-232 signals to
CMOS-logic output levels. The receiver has an inverting
three-state output and can be active or inactive. In shut-
down (FORCEOFF = low) or in AutoShutdown, the
receiver is active (Table 1). Drive EN high to place the
receiver in a high-impedance state. The receiver is high
impedance when the MAX221 is in shutdown (FORCE-
OFF = low).
The MAX221’s INVALID output is pulled low when no
valid RS-232 signal level is detected on the receiver
input. INVALID is functional in any mode (Figures 2
and 3).
AutoShutdown
The MAX221 achieves 1A supply current with Maxim’s
AutoShutdown feature, which operates when FORCEON
is low and FORCEOFF is high. When the device senses
no valid signal levels on the receiver input for 30s, the
on-board charge pump and driver are shut off, reducing
supply current to 1A. This occurs if the RS-232 cable is
disconnected or the connected peripheral transmitter is
turned off. The MAX221 turns on again when a valid
level is applied to the RS-232 receiver input. As a result,
the system saves power without changes to the existing
BIOS or operating system.
Table 1 and Figure 2c summarize the MAX221 operat-
ing modes. FORCEON and FORCEOFF override
AutoShutdown. When neither control is asserted, the
device selects between these states automatically,
based on the receiver input level. Figures 2a, 2b, and
3a depict valid and invalid RS-232 receiver levels.
Figure 3 shows the input levels and timing diagram for
AutoShutdown operation.
A device or another system with AutoShutdown con-
nected to the MAX221 may need time to wake up.
Figure 4 shows a circuit that forces the transmitter on
for 100ms, allowing enough time for the other system to
realize that the MAX221 is awake. 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 VCC, V- is pulled to ground, and the
transmitter output is high impedance. The time required
to exit shutdown is typically 100s (Figure 3b).
Software-Controlled Shutdown
For direct software control, use INVALID to indicate a
DTR or Ring Indicator signal. Connect FORCEOFF and
FORCEON together to disable AutoShutdown so the
line acts like a SHDN input.
MAX221
FORCEON
EN
12
1
ROUT
9
FORCEOFF
16
10
GND
14
TIN
11
C2-
6
C2+
5
C1-
4
C1+
2
ISHDN
RIN 8
TOUT 13
V-
7
V+
3
VCC
C4
0.1
F
0.1
F
C1
0.1
F
C2
0.1
F
CBYPASS
+5V
TO POWER-
MANAGEMENT
UNIT
5k
3k
INVALID
C3
0.1
F
15
Figure 1. Shutdown Current Test Circuit
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