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PDF MAX221 Data sheet ( Hoja de datos )
| Número de pieza | MAX221 | |
| Descripción | Single RS-232 Transceiver | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MAX221 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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19-1520; Rev 0; 8/99
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
General Description
The MAX221 is a +5V-powered, single transmit/receive
RS-232 and V.28 communications interface with auto-
matic shutdown/wake-up features and high data rate
capabilities.
The MAX221 achieves a low 1µA supply current with
Maxim’s revolutionary AutoShutdown™ feature.
AutoShutdown saves power without changes to the
existing BIOS or operating system by entering low-
power shutdown mode when the RS-232 cable is dis-
connected, or when the transmitter of the connected
peripheral is off. The MAX221 wakes up and drives the
INVALID pin high when an active RS-232 cable is con-
nected, signaling the host that a peripheral is connect-
ed to the communications port.
The MAX221 is available in a 16-pin SSOP package as
well as a 16-pin TSSOP that uses 50% less board space
than a 16-pin SO. For an equivalent RS-232 transceiver
with enhanced ±15kV ESD protection, refer to the
MAX221E data sheet.
Applications
Maintenance/Diagnostic Ports
Industrial Systems
Telecommunications
Set-Top Boxes
Features
o Single RS-232 Transceiver in a Small 16-Pin
TSSOP Package
o 1µA Supply Current
o AutoShutdown Saves Power Without
Changes to BIOS
o Guaranteed 250kbps Data Rate
PART
MAX221CUE
MAX221CAE
MAX221EUE
MAX221EAE
Ordering Information
TEMP. RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 TSSOP
16 SSOP
16 TSSOP
16 SSOP
Typical Operating Circuit
Pin Configuration
TOP VIEW
EN 1
C1+ 2
V+ 3
C1- 4
C2+ 5
C2- 6
V- 7
RIN 8
MAX221
16 FORCEOFF
15 VCC
14 GND
13 TOUT
12 FORCEON
11 TIN
10 INVALID
9 ROUT
TSSOP/SSOP
+5V
CBYPASS
C1
0.1µF
C2
0.1µF
0.1µF
2 C1+
4 C1-
5 C2+
6 C2-
11 TIN
15
VCC
MAX221
3
V+
C3
0.1µF
7
V-
TOUT 13
C4
0.1µF
9 ROUT
RIN 8
5k
1 EN
12 FORCEON
GND
14
INVALID 10
FORCEOFF 16
TO POWER-
MANAGEMENT
UNIT
VCC
AutoShutdown is a trademark of Maxim Integrated Products.
CAPACITORS MAY BE POLARIZED OR UNPOLARIZED.
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
1 page  
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
+5V ISHDN
CBYPASS
C1
0.1µF
C2
0.1µF
0.1µF
2 C1+
4 C1-
5 C2+
6 C2-
11 TIN
9 ROUT
15
VCC
MAX221
3
V+
C3
0.1µF
7
V-
TOUT 13
RIN 8
5k
C4
0.1µF
3k
1 EN
10
INVALID
12
FORCEON
GND
14
16
FORCEOFF
Figure 1. Shutdown Current Test Circuit
TO POWER-
MANAGEMENT
UNIT
_______________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 3kΩ 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 1µA 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 30µs, the
on-board charge pump and driver are shut off, reducing
supply current to 1µA. 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 100µs (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.
_______________________________________________________________________________________ 5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet MAX221.PDF ] | |
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