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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 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
♦Single RS-232 Transceiver in a Small 16-Pin
TSSOP Package
♦1µA Supply Current
♦AutoShutdown Saves Power Without
Changes to BIOS
♦Guaranteed 250kbps Data Rate
MAX221
+5V, 1µA, 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
VCC
GND
TOUT
FORCEON
TIN
INVALID
ROUT
TOP VIEW
MAX221
TSSOP/SSOP
C1+
V+
C2-
C1-
C2+
V-
RIN
MAX221
FORCEON
EN
12
1
ROUT9
FORCEOFF 16
INVALID 10
GND
14
TIN
11
C2-
6
C2+
5
C1-
4
C1+
2
RIN 8
TOUT 13
V- 7
V+ 3
VCC
VCC
C4
0.1µF
C3
0.1µF
0.1µF 15
C1
0.1µF
C2
0.1µF
CBYPASS
+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 -40°C to +85°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
16 TSSOP
16 SSOP
16 TSSOP
AutoShutdown is a trademark of Maxim Integrated Products.
Pin Configuration
Ordering Information
MAX221EAE -40°C to +85°C 16 SSOP
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +5V ±10%, C1–C4 = 0.1µF, TA= TMIN to 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
Figure 3
Figure 3
No load, TA= +25°C
Figure 3
ISOURCE = 1.0mA
ISINK = 1.6mA
CONDITIONS
ICC = 1µA, Figure 3
ROUT; ISINK = 3.2mA
Figure 3
TIN; EN, FORCEOFF, FORCEON
TA= +25°C, Figure 1
EN = VCC, 0 ≤ROUT ≤VCC
TIN = 0 to VCC
ROUT; ISOURCE = 1.0mA
µs30tINVL
Receiver Positive or Negative
Threshold to INVALID Low
µs1tINVH
Receiver Positive or Negative
Threshold to INVALID High
µs250tWU
Receiver Threshold to
Transmitter Enabled
VVCC - 0.6
INVALID Output Voltage High
V0.4
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
µA
±0.05 ±10
Negative threshold
Output Leakage Current
V
3.5
VOH
Output Voltage High
mA
510
ICC
VCC Supply Current
UNITSMIN TYP MAXSYMBOLPARAMETER
V
0.4
VOL
Output Voltage Low
V
0.8
VIL
Input Threshold Low
µA
110
ISHDN
Shutdown Supply Current
µA
110
IAS
AutoShutdown Supply Current
µA
±1
IIN
Input Leakage Current
TIN, EN, FORCEOFF V
2.4
VIH
Input Threshold High
DC CHARACTERISTICS
LOGIC INPUTS
AUTOSHUTDOWN
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
_______________________________________________________________________________________ 3
TIMING CHARACTERISTICS
(VCC = +5V ±10%, C1–C4 = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V ±10%, C1–C4 = 0.1µF, TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER
VCC = V+ = V- = 0, VOUT = ±2V
Driver loaded with 3kΩto ground
TA= +25°C, VCC = 5V
VCC = 5V, no hysteresis in shutdown
TA= +25°C, VCC = 5V
TA= +25°C, VCC = 5V
mA±10 ±60Output Short-Circuit Current
Ω300Output Resistance
V±5 ±9Output Voltage Swing
kΩ357Input Resistance
V0.5Input Hysteresis
V1.7 2.4Input Threshold High
V0.8 1.2Input Threshold Low
V-25 25Input Voltage Range
RL= 3kΩto 7kΩ, CL= 50pF to 1000pF,
VCC = 4.5V
CONDITIONS
kbps
250
Maximum Data Rate
UNITSMIN TYP MAXSYMBOLPARAMETER
TA= +25°C, VCC = 5V, RL= 3kΩto 7kΩ,
CL= 500pF to 1000pF, measured from
-3V to +3V or +3V to -3V
(Note 1)
Normal operation
Normal operation
CL= 150pF
V/µs
3630
Transition-Region Slew Rate
ns
50
|tPHL - tPLH|
Receiver Skew
ns
200
|tPHL - tPLH|
Transmitter Skew
ns
200
Receiver Output Disable Time
ns
300
Receiver Output Enable Time
µs
0.15
tPHL, tPLH
Receiver Propagation Delay
Note 1: Transmitter skew is measured at the transmitter zero crosspoints.
RECEIVER INPUT
TRANSMITTER OUTPUT
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VCC = +5V, 250kbps data rate, 0.1µF capacitors, transmitter loaded with 3kΩand CL, TA= +25°C, unless otherwise noted.)
-10
-6
-8
-2
-4
2
0
4
8
6
10
01000 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
01000 2000 3000 4000 5000
SLEW RATE vs.
LOAD CAPACITANCE
MAX221-02
LOAD CAPACITANCE (pF)
SLEW RATE (V/µs)
+SLEW
-SLEW
0
10
20
30
40
50
01000 2000 3000 4000 5000
OPERATING SUPPLY
CURRENT vs. LOAD CAPACITANCE
MAX221-03
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
250kbps
20kbps
120kbps
FUNCTIONPIN NAME
1EN 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 VCC +4.5V to +5.5V Supply Voltage
14 GND Ground
13 TOUT RS-232 Transmitter Output
MAX221
+5V, 1µA, 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 3kΩin 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.
MAX221
FORCEON
EN
12
1
ROUT9
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
0.1µF
0.1µF
C1
0.1µF
C2
0.1µF
CBYPASS
+5V
TO POWER-
MANAGEMENT
UNIT
5k
3k
INVALID
C3
0.1µF
15
Figure 1. Shutdown Current Test Circuit
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
6 _______________________________________________________________________________________
Table 1. Output Control Truth Table
1 No
Shutdown
(AutoShutdown) High-Z1 High-Z0
1
1
1
OPERATION
STATUS
X0
VALID
RECEIVER
LEVEL
EN
X
Shutdown
(Forced Off)
X
Normal Operation
(Forced On)
X0
Yes
Normal Operation
(AutoShutdown)
No
Yes0
0
High-Z
Active
Active
High-Z
TOUT
Active
High-Z
Active
0
FORCEOFF
1
0
1
1
1
1
High-Z
High-Z
Active
Active
ROUT
High-Z
Active
Active
X
FORCEON
1
X
1
0
0
0
X = Don’t care
RS-232 SIGNAL PRESENT
AT RECEIVER INPUT INVALID OUTPUT
Yes High
No Low
Table 2. INVALID Truth Table
+0.3V
-0.3V
INVALID
TO MAX221
POWER SUPPLY
AND TRANSMITTER
RIN
* TRANSMITTER IS DISABLED, REDUCING SUPPLY CURRENT TO 1µA IF
RECEIVER INPUT IS BETWEEN +0.3V AND -0.3V FOR AT LEAST 30µs.
30µs
COUNTER
R
+2.7V
-2.7V
INVALID
TO MAX221
POWER SUPPLY
RIN
* TRANSMITTER IS ENABLED IF:
RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V;
RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30µs.
30µs
COUNTER
R
Figure 2b. Transmitter Enabled Using AutoShutdown
Figure 2a. Entering 1µA Supply Mode via AutoShutdown
FORCEOFF POWER DOWN
INVALID
FORCEON
INVALID IS AN INTERNALLY GENERATED SIGNAL USED BY
THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT.
POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE
OPERATIONAL STATUS OF THE TRANSMITTER AND POWER SUPPLIES.
Figure 2c. AutoShutdown Logic
Applications Information
Using
INVALID
INVALID indicates when an RS-232 signal is present at
the receiver input, and therefore when the port is in use.
INVALID can be used in alternative shutdown control
schemes where it relieves the processor from constantly
polling the port for activity.
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; either polarized or nonpolarized
capacitors are acceptable. If polarized capacitors are
used, connect polarity as shown in the
Typical Operating
Circuit
. The charge pump requires 0.1µF capacitors.
Increasing the capacitor values (e.g., by a factor of 2)
reduces ripple on the transmitter output and slightly
reduces power consumption. C2, C3, and C4 can be
increased without changing C1’s value. However, do not
increase C1’s value without also increasing the values of
C2, C3, and C4 to maintain the proper ratios (C1 to the
other capacitors).
When using the minimum 0.1µF capacitors, make sure
the capacitance does not degrade excessively with
temperature. If in doubt, use capacitors with a larger
nominal value. The capacitor’s equivalent series resis-
tance (ESR) usually rises at low temperatures and influ-
ences the amount of ripple on V+ and V-.
Power-Supply Decoupling
In most circumstances, a 0.1µF VCC bypass capacitor
is adequate. In applications that are sensitive to power-
supply noise, use a capacitor of the same value as the
charge-pump capacitor C1. Connect bypass capaci-
tors as close to the IC as possible.
Transmitter Output when
Exiting Shutdown
Figure 5 shows the transmitter output when exiting shut-
down mode. The transmitter is loaded with 3kΩin paral-
lel with 2500pF. The transmitter output displays no
ringing or undesirable transients as the MAX221 comes
out of shutdown. Note that the transmitter is enabled only
when the magnitude of V- exceeds approximately 3V.
High Data Rates
The MAX221 maintains the RS-232 ±5.0V minimum
transmitter output voltage even at high data rates.
Figure 6 shows a transmitter loopback test circuit.
Figure 7 shows the loopback test result at 120kbps,
and Figure 8 shows the same test at 250kbps.
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
_______________________________________________________________________________________ 7
FORCEON
MASTER SHDN LINE
0.1µF1MΩ
FORCEOFF
MAX221
POWER-
MANAGEMENT
UNIT
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
Mouse or Another System
V-
VCC
0
V+
0
VCC
tINVL
tWU
INVALID
REGION
RECEIVER
INPUT
VOLTAGE
(V)
INVALID
OUTPUT
(V)
tINVH
TRANSMITTER ENABLED, INVALID HIGH
RECEIVER INPUT LEVEL
AUTOSHUTDOWN, TRANSMITTER DISABLED,
1µA SUPPLY CURRENT, INVALID LOW
TRANSMITTER ENABLED, INVALID HIGH
-2.7V
-0.3V
+2.7V
+0.3V
0
INDETERMINATE
INDETERMINATE
b)
a)
Figure 3. AutoShutdown Trip Levels
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8
_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
TRANSISTOR COUNT: 157
___________________Chip Information
2µs/div
5V/div
5V/div
5V/div
TIN
TOUT
ROUT
Figure 7. Loopback Test Result at 120kbps
Figure 8. Loopback Test Result at 250kbps
2µs/div
5V/div
5V/div
5V/div
TIN
TOUT
ROUT
Figure 6. Loopback Test Circuit
MAX221
5k
RIN
ROUT
EN
C2-
C2+
C1-
C1+
V-
V+
VCC
C4
C3
C1
C2
0.1µF
+5V
FORCEOFF
FORCEON INVALID
TOUT
TIN
GND
VCC
0V
1000pF
5V/div FORCEON =
FORCEOFF
TOUT
5V/div
50µs/div
TIN = GND
TIN = VCC
Figure 5. Transmitter Output Exiting Shutdown or
Powering Up
