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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 1A supply current with
Maxim's revolutionary AutoShutdownTM 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
1A Supply Current
o
AutoShutdown Saves Power Without
Changes to BIOS
o
Guaranteed 250kbps Data Rate
MAX221
+5V, 1A, Single RS-232 Transceiver
with AutoShutdown
________________________________________________________________
Maxim Integrated Products
1
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
EN
FORCEOFF
V
CC
GND
TOUT
FORCEON
TIN
INVALID
ROUT
TOP VIEW
MAX221
TSSOP/SSOP
C1+
V+
C2-
C1-
C2+
V-
RIN
MAX221
FORCEON
EN
12
1
ROUT
9
FORCEOFF
16
INVALID
10
GND
14
TIN
11
C2-
6
C2+
5
C1-
4
C1+
2
RIN 8
TOUT 13
V-
7
V+
3
V
CC
V
CC
C4
0.1
F
C3
0.1
F
0.1
F
15
C1
0.1
F
C2
0.1
F
C
BYPASS
+5V
TO POWER-
MANAGEMENT
UNIT
CAPACITORS MAY BE POLARIZED OR UNPOLARIZED.
5k
Typical Operating Circuit
19-1520; Rev 0; 8/99
PART
MAX221CUE
MAX221CAE
MAX221EUE
-40C to +85C
0C to +70C
0C to +70C
TEMP. RANGE
PIN-PACKAGE
16 TSSOP
16 SSOP
16 TSSOP
AutoShutdown is a trademark of Maxim Integrated Products.
Pin Configuration
Ordering Information
MAX221EAE
-40C to +85C
16 SSOP
MAX221
+5V, 1A, Single RS-232 Transceiver
with AutoShutdown
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
CC
= +5V 10%, C1C4 = 0.1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25C.)
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.
V
CC
..........................................................................-0.3V to +6V
V+ ...............................................................(V
CC
- 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 (V
CC
+ 0.3V)
Output Voltages
TOUT ..............................................(V- - 0.3V) to (V+ + 0.3V)
ROUT, INVALID ....................................-0.3V to (V
CC
+ 0.3V)
Short-Circuit Duration, TOUT .....................................Continuous
Continuous Power Dissipation (T
A
= +70C)
TSSOP (derated 6.7mW/C above +70C) ................533mW
SSOP (derated 7.1mW/C above +70C) ..................571mW
Operating Temperature Range
MAX221C_ _ .....................................................0C to +70C
MAX221E_ _ ..................................................-40C to +85C
Maximum Junction Temperature ................................... +150C
Storage Temperature Range ........................... -65C to +150C
Lead Temperature (soldering, 10sec) ............................ +300C
Figure 3
Figure 3
No load, T
A
= +25C
Figure 3
I
SOURCE
= 1.0mA
I
SINK
= 1.6mA
CONDITIONS
I
CC
= 1A, Figure 3
ROUT; I
SINK
= 3.2mA
Figure 3
TIN; EN, FORCEOFF, FORCEON
T
A
= +25C, Figure 1
EN = V
CC
, 0
ROUT
V
CC
TIN = 0 to V
CC
ROUT; I
SOURCE
= 1.0mA
s
30
t
INVL
Receiver Positive or Negative
Threshold to INVALID Low
s
1
t
INVH
Receiver Positive or Negative
Threshold to INVALID High
s
250
t
WU
Receiver Threshold to
Transmitter Enabled
V
V
CC
- 0.6
INVALID Output Voltage High
V
0.4
INVALID Output Voltage Low
V
-0.3
0.3
Receiver Input Threshold,
Transmitter Disabled
-2.7
Positive threshold
V
2.7
Receiver Input Threshold,
Transmitter Enabled
A
0.05
10
Negative threshold
Output Leakage Current
V
3.5
V
OH
Output Voltage High
mA
5
10
I
CC
V
CC
Supply Current
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
V
0.4
V
OL
Output Voltage Low
V
0.8
V
IL
Input Threshold Low
A
1
10
I
SHDN
Shutdown Supply Current
A
1
10
I
AS
AutoShutdown Supply Current
A
1
I
IN
Input Leakage Current
TIN, EN, FORCEOFF
V
2.4
V
IH
Input Threshold High
DC CHARACTERISTICS
LOGIC INPUTS
AUTOSHUTDOWN
MAX221
+5V, 1A, Single RS-232 Transceiver
with AutoShutdown
_______________________________________________________________________________________
3
TIMING CHARACTERISTICS
(V
CC
= +5V 10%, C1C4 = 0.1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25C.)
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +5V 10%, C1C4 = 0.1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25C.)
CONDITIONS
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
V
CC
= V+ = V- = 0, V
OUT
= 2V
Driver loaded with 3k
to ground
T
A
= +25C, V
CC
= 5V
V
CC
= 5V, no hysteresis in shutdown
T
A
= +25C, V
CC
= 5V
T
A
= +25C, V
CC
= 5V
mA
10
60
Output Short-Circuit Current
300
Output Resistance
V
5
9
Output Voltage Swing
k
3
5
7
Input Resistance
V
0.5
Input Hysteresis
V
1.7
2.4
Input Threshold High
V
0.8
1.2
Input Threshold Low
V
-25
25
Input Voltage Range
R
L
= 3k
to 7k
, C
L
= 50pF to 1000pF,
V
CC
= 4.5V
CONDITIONS
kbps
250
Maximum Data Rate
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
T
A
= +25C, V
CC
= 5V, R
L
= 3k
to 7k
,
C
L
= 500pF to 1000pF, measured from
-3V to +3V or +3V to -3V
(Note 1)
Normal operation
Normal operation
C
L
= 150pF
V/s
3
6
30
Transition-Region Slew Rate
ns
50
|
t
PHL
- t
PLH
|
Receiver Skew
ns
200
|
t
PHL
- t
PLH
|
Transmitter Skew
ns
200
Receiver Output Disable Time
ns
300
Receiver Output Enable Time
s
0.15
t
PHL,
t
PLH
Receiver Propagation Delay
Note 1:
Transmitter skew is measured at the transmitter zero crosspoints.
RECEIVER INPUT
TRANSMITTER OUTPUT
MAX221
+5V, 1A, Single RS-232 Transceiver
with AutoShutdown
4
_______________________________________________________________________________________
Typical Operating Characteristics
(V
CC
= +5V, 250kbps data rate, 0.1F capacitors, transmitter loaded with 3k
and C
L
, T
A
= +25C, unless otherwise noted.)
-10
-6
-8
-2
-4
2
0
4
8
6
10
0
1000
2000
3000
4000
5000
TRANSMITTER OUTPUT
VOLTAGE vs. LOAD CAPACITANCE
MAX221-01
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
250kbps
250kbps
120kbps
20kbps
20kbps
120kbps
0
10
20
30
40
50
0
1000
2000
3000
4000
5000
SLEW RATE vs.
LOAD CAPACITANCE
MAX221-02
LOAD CAPACITANCE (pF)
SLEW RATE (V/
s)
+SLEW
-SLEW
0
10
20
30
40
50
0
1000
2000
3000
4000
5000
OPERATING SUPPLY
CURRENT vs. LOAD CAPACITANCE
MAX221-03
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
250kbps
20kbps
120kbps
FUNCTION
PIN
NAME
1
EN
Receiver Enable Control. Drive low for normal operation. Drive high to force the receiver output
(ROUT) into a high-impedance state.
2
C1+
Positive Terminal of the Voltage Doubler Charge-Pump Capacitor
3
V+
Positive Voltage Generated by the Charge Pump
7
V-
Negative Voltage Generated by the Charge Pump
6
C2-
Negative Terminal of the Inverting Charge-Pump Capacitor
5
C2+
Positive Terminal of the Inverting Charge-Pump Capacitor
4
C1-
Negative Terminal of the Voltage Doubler Charge-Pump Capacitor
12
FORCEON
Drive high to override automatic circuitry, keeping transmitter and charge pump on.
FORCEOFF must be high (Table 1).
11
TIN
TTL/CMOS Transmitter Input
10
INVALID
Output of the Invalid Signal Detector. INVALID is pulled low if no valid RS-232 level is present on
the receiver input.
9
ROUT
TTL/CMOS Receiver Output
8
RIN
RS-232 Receiver Input
Pin Description
16
FORCEOFF
Force-Off Input, active low. Drive low to shut down transmitter, receiver, and on-board charge
pump. This overrides all automatic circuitry and FORCEON (Table 1).
15
V
CC
+4.5V to +5.5V Supply Voltage
14
GND
Ground
13
TOUT
RS-232 Transmitter Output
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 V
CC
, 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
I
SHDN
RIN 8
TOUT 13
V-
7
V+
3
V
CC
C4
0.1
F
0.1
F
C1
0.1
F
C2
0.1
F
C
BYPASS
+5V
TO POWER-
MANAGEMENT
UNIT
5k
3k
INVALID
C3
0.1
F
15
Figure 1. Shutdown Current Test Circuit
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