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19-1520; Rev 0; 8/99
+5V, 1A, 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 automatic 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 lowpower shutdown mode when the RS-232 cable is disconnected, 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 connected, signaling the host that a peripheral is connected 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 1A 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 0C to +70C 0C to +70C -40C to +85C -40C to +85C 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 VCC V+ 3 C3 0.1F
Pin Configuration
TOP VIEW
EN 1 C1+ 2 V+ 3 C1- 4 C2+ 5 C2- 6 V- 7 RIN 8 16 FORCEOFF 15 VCC 14 GND
CBYPASS C1 0.1F
0.1F 2 C1+ 4 C15 C2+ C2-
MAX221
V-
7 C4 0.1F
C2 0.1F
6
11 TIN
TOUT 13
MAX221
13 TOUT 12 FORCEON 11 TIN 10 INVALID 9 ROUT 1 EN INVALID 10 TO POWERMANAGEMENT UNIT VCC 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, 1A, Single RS-232 Transceiver with AutoShutdown MAX221
ABSOLUTE MAXIMUM RATINGS
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 = +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
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
(VCC = +5V 10%, C1-C4 = 0.1F, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER DC CHARACTERISTICS VCC 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 tWU tINVH tINVL Figure 3 ICC = 1A, Figure 3 ISINK = 1.6mA ISOURCE = 1.0mA Figure 3 Figure 3 Figure 3 VCC - 0.6 250 1 30 Positive threshold Negative threshold -2.7 -0.3 0.3 0.4 2.7 V V V V s s s IIN VIL VIH VOL VOH TIN = 0 to VCC TIN; EN, FORCEOFF, FORCEON TIN, EN, FORCEOFF ROUT; ISINK = 3.2mA ROUT; ISOURCE = 1.0mA EN = VCC, 0 ROUT VCC 3.5 0.05 10 2.4 0.4 1 0.8 A V V V V A ICC ISHDN IAS No load, TA = +25C TA = +25C, Figure 1 5 1 1 10 10 10 mA A A SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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+5V, 1A, Single RS-232 Transceiver with AutoShutdown
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V 10%, C1-C4 = 0.1F, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) 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 3k to ground VCC = V+ = V- = 0, VOUT = 2V 5 300 10 60 9 V mA TA = +25C, VCC = 5V TA = +25C, VCC = 5V VCC = 5V, no hysteresis in shutdown TA = +25C, VCC = 5V 3 -25 0.8 1.2 1.7 0.5 5 7 2.4 25 V V V V k SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX221
TIMING CHARACTERISTICS
(VCC = +5V 10%, C1-C4 = 0.1F, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Maximum Data Rate Receiver Propagation Delay Receiver Output Enable Time Receiver Output Disable Time Transmitter Skew Receiver Skew Transition-Region Slew Rate tPHL, tPLH SYMBOL CONDITIONS RL = 3k to 7k, CL = 50pF to 1000pF, VCC = 4.5V CL = 150pF Normal operation Normal operation MIN 250 0.15 300 200 200 50 TA = +25C, VCC = 5V, RL = 3k to 7k, CL = 500pF to 1000pF, measured from -3V to +3V or +3V to -3V 3 6 30 TYP MAX UNITS kbps s ns ns ns ns V/s
| tPHL - tPLH| | tPHL - tPLH |
(Note 1)
Note 1: Transmitter skew is measured at the transmitter zero crosspoints.
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3
+5V, 1A, Single RS-232 Transceiver with AutoShutdown MAX221
Typical Operating Characteristics
(VCC = +5V, 250kbps data rate, 0.1F capacitors, transmitter loaded with 3k and CL, TA = +25C, 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/s) +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+ C1C2+ C2VRIN ROUT INVALID TIN FORCEON TOUT GND VCC 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
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+5V, 1A, Single RS-232 Transceiver with AutoShutdown
+5V CBYPASS C1 0.1F ISHDN 0.1F 2 C1+ 4 C15 C2 0.1F 6 C2+ C2TOUT 13 3k 9 ROUT 5k RIN 8 15 VCC V+ 3 C3 0.1F
MAX221
V-
7 C4 0.1F
11 TIN
three-state output and can be active or inactive. In shutdown (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 (FORCEOFF = 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 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 operating 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 connected 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 RS232 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 100s (Figure 3b).
1
EN
INVALID FORCEOFF
10
TO POWERMANAGEMENT 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 (inverting 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 Vsupplies.
RS-232 Transmitter
The transmitter is an inverting level translator that converts 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 output 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
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5
+5V, 1A, Single RS-232 Transceiver with AutoShutdown MAX221
Table 1. Output Control Truth Table
OPERATION STATUS FORCEON FORCEOFF EN VALID RECEIVER LEVEL TOUT ROUT
Shutdown (Forced Off) Normal Operation (Forced On) Normal Operation (AutoShutdown) Shutdown (AutoShutdown)
X X 1 1 0 0 0 0
0 0 1 1 1 1 1 1
0 1 0 1 0 1 0 1
X X X X Yes Yes No No
High-Z High-Z Active Active Active Active High-Z High-Z
Active High-Z Active High-Z Active High-Z Active High-Z
X = Don't care
+0.3V TO MAX221 POWER SUPPLY AND TRANSMITTER INVALID
FORCEOFF FORCEON INVALID
POWER DOWN
RIN
-0.3V
30s COUNTER R
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.
* TRANSMITTER IS DISABLED, REDUCING SUPPLY CURRENT TO 1A IF RECEIVER INPUT IS BETWEEN +0.3V AND -0.3V FOR AT LEAST 30s.
Figure 2a. Entering 1A Supply Mode via AutoShutdown
Figure 2c. AutoShutdown Logic
Table 2. INVALID Truth Table
+2.7V TO MAX221 POWER SUPPLY INVALID
RS-232 SIGNAL PRESENT AT RECEIVER INPUT
30s COUNTER R
INVALID OUTPUT High Low
RIN
Yes No
-2.7V
* 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 30s.
Figure 2b. Transmitter Enabled Using AutoShutdown
6
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+5V, 1A, Single RS-232 Transceiver with AutoShutdown
Applications Information
Using INVALID
TRANSMITTER ENABLED, INVALID HIGH RECEIVER INPUT LEVEL +2.7V INDETERMINATE +0.3V 0 -0.3V INDETERMINATE -2.7V TRANSMITTER ENABLED, INVALID HIGH AUTOSHUTDOWN, TRANSMITTER DISABLED, 1A SUPPLY CURRENT, INVALID LOW
MAX221
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 0.1F 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 0.1F 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 resistance (ESR) usually rises at low temperatures and influences the amount of ripple on V+ and V-.
a)
RECEIVER INPUT VOLTAGE (V)
INVALID REGION
VCC INVALID OUTPUT (V) 0
tINVL
tINVH tWU
Power-Supply Decoupling
In most circumstances, a 0.1F VCC bypass capacitor is adequate. In applications that are sensitive to powersupply noise, use a capacitor of the same value as the charge-pump capacitor C1. Connect bypass capacitors as close to the IC as possible.
V+ VCC 0 V-
b)
Transmitter Output when Exiting Shutdown
Figure 5 shows the transmitter output when exiting shutdown mode. The transmitter is loaded with 3k in parallel 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.
Figure 3. AutoShutdown Trip Levels
POWERMANAGEMENT UNIT
MASTER SHDN LINE 0.1F 1M
High Data Rates
FORCEOFF FORCEON
MAX221
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.
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a Mouse or Another System
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+5V, 1A, Single RS-232 Transceiver with AutoShutdown MAX221
5V/div TIN = GND FORCEON = FORCEOFF 5V/div TIN
5V/div
TOUT
5V/div
TOUT
TIN = VCC 5V/div ROUT
50s/div
2s/div
Figure 5. Transmitter Output Exiting Shutdown or Powering Up
Figure 7. Loopback Test Result at 120kbps
+5V 0.1F C3 C1+ C1 C1C2+ C2 C2TIN ROUT 0V VCC EN FORCEOFF FORCEON 5k 1000pF GND INVALID TOUT RIN 5V/div ROUT VCC 5V/div TIN
V+ 5V/div VC4 TOUT
MAX221
2s/div
Figure 8. Loopback Test Result at 250kbps
___________________Chip Information
TRANSISTOR COUNT: 157
Figure 6. Loopback Test Circuit
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 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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