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.
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
MAX221
Ordering Information
PART
MAX221CUE
MAX221CAE
MAX221EUE
MAX221EAE
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
Applications
Maintenance/Diagnostic Ports
Industrial Systems
Telecommunications
Set-Top Boxes
+5V
Typical Operating Circuit
15
V
CC
V+
3
C3
0.1µF
Pin Configuration
TOP VIEW
EN 1
C1+ 2
V+ 3
C1- 4
C2+ 5
C2- 6
V- 7
RIN 8
16 FORCEOFF
15 V
CC
14 GND
C
BYPASS
C1
0.1µF
0.1µF
2 C1+
4 C1-
5
C2+
C2-
MAX221
V-
7
C4
0.1µF
C2
0.1µF
6
11 TIN
TOUT 13
MAX221
13 TOUT
12 FORCEON
11 TIN
10 INVALID
9
ROUT
1
EN
INVALID
10
TO POWER-
MANAGEMENT
UNIT
V
CC
9 ROUT
5k
RIN 8
TSSOP/SSOP
12
FORCEON
GND
14
FORCEOFF
16
CAPACITORS MAY BE POLARIZED OR UNPOLARIZED.
AutoShutdown is a trademark of Maxim Integrated Products.
________________________________________________________________
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.
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
MAX221
ABSOLUTE MAXIMUM RATINGS
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
= +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
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.
ELECTRICAL CHARACTERISTICS
(V
CC
= +5V ±10%, C1–C4 = 0.1µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
DC CHARACTERISTICS
V
CC
Supply Current
Shutdown Supply Current
AutoShutdown Supply Current
LOGIC INPUTS
Input Leakage Current
Input Threshold Low
Input Threshold High
Output Voltage Low
Output Voltage High
Output Leakage Current
AUTOSHUTDOWN
Receiver Input Threshold,
Transmitter Enabled
Receiver Input Threshold,
Transmitter Disabled
INVALID
Output Voltage Low
INVALID
Output Voltage High
Receiver Threshold to
Transmitter Enabled
Receiver Positive or Negative
Threshold to
INVALID
High
Receiver Positive or Negative
Threshold to
INVALID
Low
t
WU
t
INVH
t
INVL
Figure 3
I
CC
= 1µA, Figure 3
I
SINK
= 1.6mA
I
SOURCE
= 1.0mA
Figure 3
Figure 3
Figure 3
V
CC
- 0.6
250
1
30
Positive threshold
Negative threshold
-2.7
-0.3
0.3
0.4
2.7
V
V
V
V
µs
µs
µs
I
IN
V
IL
V
IH
V
OL
V
OH
TIN = 0 to V
CC
TIN;
EN, FORCEOFF,
FORCEON
TIN,
EN, FORCEOFF
ROUT; I
SINK
= 3.2mA
ROUT; I
SOURCE
= 1.0mA
EN
= V
CC
, 0
≤
ROUT
≤
V
CC
3.5
±0.05
±10
2.4
0.4
±1
0.8
µA
V
V
V
V
µA
I
CC
I
SHDN
I
AS
No load, T
A
= +25°C
T
A
= +25°C, Figure 1
5
1
1
10
10
10
mA
µA
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +5V ±10%, C1–C4 = 0.1µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
RECEIVER INPUT
Input Voltage Range
Input Threshold Low
Input Threshold High
Input Hysteresis
Input Resistance
TRANSMITTER OUTPUT
Output Voltage Swing
Output Resistance
Output Short-Circuit Current
Driver loaded with 3kΩ to ground
V
CC
= V+ = V- = 0, V
OUT
= ±2V
±5
300
±10
±60
±9
V
Ω
mA
T
A
= +25°C, V
CC
= 5V
T
A
= +25°C, V
CC
= 5V
V
CC
= 5V, no hysteresis in shutdown
T
A
= +25°C, V
CC
= 5V
3
-25
0.8
1.2
1.7
0.5
5
7
2.4
25
V
V
V
V
kΩ
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX221
TIMING CHARACTERISTICS
(V
CC
= +5V ±10%, C1–C4 = 0.1µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Maximum Data Rate
Receiver Propagation Delay
Receiver Output Enable Time
Receiver Output Disable Time
Transmitter Skew
Receiver Skew
Transition-Region Slew Rate
t
PHL,
t
PLH
SYMBOL
CONDITIONS
R
L
= 3kΩ to 7kΩ, C
L
= 50pF to 1000pF,
V
CC
= 4.5V
C
L
= 150pF
Normal operation
Normal operation
MIN
250
0.15
300
200
200
50
T
A
= +25°C, V
CC
= 5V, R
L
= 3kΩ to 7kΩ,
C
L
= 500pF to 1000pF, measured from
-3V to +3V or +3V to -3V
3
6
30
TYP
MAX
UNITS
kbps
µs
ns
ns
ns
ns
V/µs
|
t
PHL
- t
PLH
|
|
t
PHL
- t
PLH
|
(Note 1)
Note 1:
Transmitter skew is measured at the transmitter zero crosspoints.
_______________________________________________________________________________________
3
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
MAX221
Typical Operating Characteristics
(V
CC
= +5V, 250kbps data rate, 0.1µF capacitors, transmitter loaded with 3kΩ and C
L
, T
A
= +25°C, unless otherwise noted.)
TRANSMITTER OUTPUT
VOLTAGE vs. LOAD CAPACITANCE
TRANSMITTER OUTPUT VOLTAGE (V)
8
6
4
2
0
-2
-4
-6
-8
-10
0
1000
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
0
0
1000
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
0
0
1000
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
20kbps
120kbps
10
250kbps
20kbps
120kbps
250kbps
MAX221-01
SLEW RATE vs.
LOAD CAPACITANCE
MAX221-02
OPERATING SUPPLY
CURRENT vs. LOAD CAPACITANCE
MAX221-03
10
50
50
40
SUPPLY CURRENT (mA)
SLEW RATE (V/µs)
+SLEW
30
-SLEW
20
40
250kbps
30
20
10
120kbps
20kbps
Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NAME
EN
C1+
V+
C1-
C2+
C2-
V-
RIN
ROUT
INVALID
TIN
FORCEON
TOUT
GND
V
CC
FORCEOFF
FUNCTION
Receiver Enable Control. Drive low for normal operation. Drive high to force the receiver output
(ROUT) into a high-impedance state.
Positive Terminal of the Voltage Doubler Charge-Pump Capacitor
Positive Voltage Generated by the Charge Pump
Negative Terminal of the Voltage Doubler Charge-Pump Capacitor
Positive Terminal of the Inverting Charge-Pump Capacitor
Negative Terminal of the Inverting Charge-Pump Capacitor
Negative Voltage Generated by the Charge Pump
RS-232 Receiver Input
TTL/CMOS Receiver Output
Output of the Invalid Signal Detector.
INVALID
is pulled low if no valid RS-232 level is present on
the receiver input.
TTL/CMOS Transmitter Input
Drive high to override automatic circuitry, keeping transmitter and charge pump on.
FORCEOFF
must be high (Table 1).
RS-232 Transmitter Output
Ground
+4.5V to +5.5V Supply Voltage
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).
4
_______________________________________________________________________________________
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
+5V
C
BYPASS
C1
0.1µF
I
SHDN
0.1µF
2 C1+
4 C1-
5
C2
0.1µF
6
C2+
C2-
TOUT 13
3k
9 ROUT
5k
RIN 8
15
V
CC
V+
3
C3
0.1µF
MAX221
V-
7
C4
0.1µF
11 TIN
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).
MAX221
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 V
CC
, V- is pulled to ground, and the
transmitter output is high impedance. The time required
to exit shutdown is typically 100µs (Figure 3b).
1
EN
INVALID
FORCEOFF
10
TO POWER-
MANAGEMENT
UNIT
12
FORCEON
16
GND
14
Figure 1. Shutdown Current Test Circuit
_______________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.
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.
RS-232 Receiver
The MAX221’s receiver converts RS-232 signals to
CMOS-logic output levels. The receiver has an inverting
_______________________________________________________________________________________
5
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