MAX221CUE ,%V, 1レA, Single RS-232 Transceiver with AutoShutdownELECTRICAL CHARACTERISTICS(V = +5V ±10%, C1–C4 = 0.1μF, T = T to T , unless otherwise noted. Typica ..
MAX221CUE ,%V, 1レA, Single RS-232 Transceiver with AutoShutdownApplicationsMaintenance/Diagnostic PortsIndustrial SystemsTelecommunications Typical Operating Circ ..
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MAX221CUE
%V, 1レA, Single RS-232 Transceiver with AutoShutdown
General DescriptionThe 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 theINVALIDpin 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.
ApplicationsMaintenance/Diagnostic Ports
Industrial Systems
Telecommunications
Set-Top Boxes
FeaturesSingle RS-232 Transceiver in a Small 16-Pin
TSSOP Package1μA Supply CurrentAutoShutdown Saves Power Without
Changes to BIOSGuaranteed 250kbps Data Rate
MAX221
+5V, 1μA, Single RS-232 Transceiver
with AutoShutdownypical Operating Circuit19-1520; Rev 0; 8/99
Pin Configuration
Ordering Information
MAX221
+5V, 1μA, Single RS-232 Transceiver
with AutoShutdown
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC = +5V ±10%, C1–C4 = 0.1μF, TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VCC..........................................................................-0.3V to +6V
V+ ...............................................................(VCC- 0.3V) to +14V
V- ...........................................................................-14V to +0.3V
Input Voltages
TIN..........................................................-0.3V to (V+ + 0.3V)
RIN.................................................................................±30V
FORCEON, FORCEOFF, EN.................-0.3V to (VCC+ 0.3V)
Output Voltages
TOUT..............................................(V- - 0.3V) to (V+ + 0.3V)
ROUT, INVALID....................................-0.3V to (VCC+ 0.3V)
Short-Circuit Duration, TOUT.....................................Continuous
Continuous Power Dissipation (TA= +70°C)
TSSOP (derated 6.7mW/°C above +70°C)................533mW
SSOP (derated 7.1mW/°C above +70°C)..................571mW
Operating Temperature Range
MAX221C_ _.....................................................0°C to +70°C
MAX221E_ _..................................................-40°C to +85°C
Maximum Junction Temperature ...................................+150°C
Storage Temperature Range ...........................-65°C to +150°C
Lead Temperature (soldering, 10sec)............................+300°C
MAX221
+5V, 1μA, Single RS-232 Transceiver
with AutoShutdown
TIMING CHARACTERISTICS(VCC= +5V ±10%, C1–C4 = 0.1μF, TA = TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
ELECTRICAL CHARACTERISTICS (continued)(VCC = +5V ±10%, C1–C4 = 0.1μF, TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
Note 1:Transmitter skew is measured at the transmitter zero crosspoints.
MAX221
+5V, 1μA, Single RS-232 Transceiver
with AutoShutdown
Typical Operating Characteristics(VCC= +5V, 250kbps data rate, 0.1μF capacitors, transmitter loaded with 3kWand CL, TA= +25°C, unless otherwise noted.)
Pin Description
MAX221
+5V, 1μA, Single RS-232 Transceiver
with AutoShutdown
_______________Detailed Description
Dual Charge-Pump Voltage ConverterThe 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 TransmitterThe 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 3kΩin parallel with 1000pF.
When FORCEOFFis 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 ReceiverThe 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 ENhigh 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 INVALIDoutput is pulled low when no
valid RS-232 signal level is detected on the receiver
input. INVALIDis functional in any mode (Figures 2
and 3).
AutoShutdownThe MAX221 achieves 1μA supply current with Maxim’s
AutoShutdown feature, which operates when FORCEON
is low and FORCEOFFis 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 FORCEOFFoverride
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 ShutdownFor direct software control, use INVALIDto indicate a
DTR or Ring Indicator signal. Connect FORCEOFFand
FORCEON together to disable AutoShutdown so the
line acts like a SHDNinput.
MAX221
+5V, 1μA, Single RS-232 Transceiver
with AutoShutdown
Table 1. Output Control Truth TableX = Don’t care
Table 2. INVALIDTruth TableFigure 2c. AutoShutdown Logic
