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19-0246; Rev 1; 7/95
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver
_______________General Description
The MAX218 RS-232 transceiver is intended for batterypowered EIA/TIA-232E and V.28/V.24 communications interfaces that need two drivers and two receivers with minimum power consumption. It provides a wide +1.8V to +4.25V operating voltage range while maintaining true RS-232 and EIA/TIA-562 voltage levels. The MAX218 runs from two alkaline, NiCd, or NiMH cells without any form of voltage regulator. A shutdown mode reduces current consumption to 1A, extending battery life in portable systems. While shut down, all receivers can remain active or can be disabled under logic control, permitting a system incorporating the CMOS MAX218 to monitor external devices while in low-power shutdown mode. A guaranteed 120kbps data rate provides compatibility with popular software for communicating with personal computers. Three-state drivers are provided on all receiver outputs so that multiple receivers, generally of different interface standards, can be wire-ORed at the UART. The MAX218 is available in 20-pin DIP, SO, and SSOP packages.
____________________________Features
BETTER THAN BIPOLAR! o Operates Directly from Two Alkaline, NiCd, or NiMH Cells o +1.8V to +4.25V Supply Voltage Range o 120kbps Data Rate o Low-Cost Surface-Mount Components o Meets EIA/TIA-232E Specifications o 1A Low-Power Shutdown Mode o Both Receivers Active During Low-Power Shutdown o Three-State Receiver Outputs o Flow-Through Pinout o On-Board DC-DC Converters o 20-Pin SSOP, Wide SO, or DIP Packages
MAX218
______________Ordering Information
PART MAX218CPP MAX218CWP MAX218CAP MAX218C/D MAX218EPP MAX218EWP MAX218EAP TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 20 Plastic DIP 20 Wide SO 20 SSOP Dice* 20 Plastic DIP 20 Wide SO 20 SSOP
________________________Applications
Battery-Powered Equipment Computers Printers Peripherals Instruments Modems
*Contact factory for dice specifications.
__________Typical Operating Circuit
1 LX VCC 19 V+ V-
__________________Pin Configuration
TOP VIEW
LX 1 20 GND 19 V+ 18 C1+ 17 GND
1.8V TO 4.25V
6
15
N.C. 2 SHDN 3 EN 4 GND 5 VCC 6
ON/OFF
3
MAX218
SHDN T1 T2 R1 R2 4
C1+ 18 C116
7 T1IN 8 T2IN 9 R1OUT 10 R2OUT EN ENABLE
T1OUT 14 T2OUT 13 R1IN 12 R2IN 11 GND 5, 17, 20
MAX218
16 C115 V14 T1OUT 13 T2OUT 12 R1IN 11 R2IN
T1IN 7 T2IN 8 R1OUT 9 R2OUT 10
DIP/SO/SSOP 1
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver MAX218
ABSOLUTE MAXIMUM RATINGS
Supply Voltages VCC ....................................................................-0.3V to +4.6V V+ .......................................................... (VCC - 0.3V) to +7.5V V- .......................................................................+0.3V to -7.4V VCC to V- ..........................................................................+12V LX ................................................................-0.3V to (1V + V+) Input Voltages-- - ---- T_IN, EN, SHDN ................................................. -0.3V to +7V R_IN .................................................................................25V Output Voltages T_OUT.............................................................................15V) R_OUT ....................................................-0.3V to (VCC + 0.3V) Short-Circuit Duration, R_OUT, T_OUT to GND ....... Continuous Continuous Power Dissipation (TA = +70C) Plastic DIP (derate 11.11mW/C above +70C) ..........889mW Wide SO (derate 10.00mW/C above +70C)..............800mW SSOP (derate 8.00mW/C above +70C) ...................640mW Operating Temperature Ranges MAX218C_ P ..................................................... 0C to +70C MAX218E_ P ................................................... -40C to +85C 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
(Circuit of Figure 1, VCC = 1.8V to 4.25V, C1 = 0.47F, C2 = C3 = C4 = 1F, L1 = 15H, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.0V, TA = +25C.) PARAMETER DC CHARACTERISTICS Operating Voltage Range Supply Current (Note 1) Shutdown Supply Current LOGIC Input Logic Threshold Low Input Logic Threshold High Input Hysteresis Input Leakage Current Output Voltage Low Output Voltage High Output Leakage Current Input Voltage Range Input Threshold Low Input Threshold High Input Hysteresis Input Resistance Output Voltage Swing Output Resistance Output Short-Circuit Current Note 1: Entire supply current for the circuit of Figure 1. -15V < R_IN < +15V All transmitter outputs loaded with 3k to ground VCC = 0V, -2V < T_OUT < +2V 3 5 300 24 100 EIA/TIA-232E TRANSMITTER OUTPUTS 6 V mA VCC = 2.0V to 4.25V VCC = 1.8V to 4.25V VCC = 1.8V to 4.25V VCC = 1.8V to 3.6V 0.7 5 7 ---- --- T_IN, EN, SHDN ---- --- T_IN, EN, SHDN T_IN ---- --- T_IN, EN, SHDN = 0V or VCC R_OUT, IOUT = 1.0mA R_OUT, IOUT = -0.4mA R_OUT, 0V R_OUT VCC, EN = 0V -25 0.4 0.3 3.0 2.8 VCC - 0.25 VCC - 0.08 0.05 10 +25 0.33 x VCC 0.67 x VCC 0.1 0.001 1 0.4 V V V A V V A V V V V k ---- --- No load, VCC = EN = SHDN = 3.0V, TA = +25C ---- --- SHDN = EN = 0V, all R_INs static ---- --- SHDN = 0V, EN = VCC, all R_INs static 1.8 1.9 0.04 0.04 4.25 3.0 10 10 V mA A CONDITIONS MIN TYP MAX UNITS
EIA/TIA-232E RECEIVER INPUTS
2
_______________________________________________________________________________________
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver
TIMING CHARACTERISTICS
(Circuit of Figure 1, VCC = 1.8V to 4.25V, C1 = 0.47F, C2 = C3 = C4 = 1F, L1 = 15H, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.0V, TA = +25C.) PARAMETER Data Rate Receiver Output Enable Time Receiver Output Disable Time Transmitter Output Enable Time Transmitter Output Disable Time Receiver Propagation Delay Transmitter Propagation Delay tER tDR tET tDT tPHLR tPLHR tPHLT tPLHT 150pF load 150pF load 2500pF || 3k load 2500pF || 3k load TA = +25C, VCC = 3.0V, RL = 3k to 7k, CL = 50pF to 2500pF, measured from +3V to -3V or -3V to +3V 3.0 SYMBOL CONDITIONS 1000pF || 3k load each transmitter, 150pF load each receiver MIN 120 90 200 140 500 290 260 1.9 1.8 700 700 2.7 2.7 30 300 500 450 TYP MAX UNITS kbps ns ns s ns ns s
MAX218
Transition Region Slew Rate
V/s
______________________________________________________________Pin Description
PIN 1 2 3 NAME LX N.C. ---- --- SHDN Inductor/Diode Connection Point Not internally connected Shutdown Control. Connect to VCC for normal operation. Connect to GND to shut down the power supply and to disable the drivers. Receiver status is not changed by this control. Receiver Output Enable Control. Connect to VCC for normal operation. Connect to GND to force the receiver outputs into high-Z state. Ground. Connect all GND pins to ground. Supply Voltage Input; 1.8V to 4.25V. Bypass to GND with at least 1F. See Capacitor Selection section. Transmitter Inputs Receiver Outputs; swing between GND and VCC. Receiver Inputs Transmitter Outputs; swing between V+ and V-. Negative Supply generated on-board Terminals for Negative Charge-Pump Capacitor Positive Supply generated on-board FUNCTION
4 5, 17, 20 6 7, 8 9, 10 11, 12 13, 14 15 16, 18 19
EN GND VCC T1IN, T2IN R1OUT, R2OUT R2IN, R1IN T2OUT, T1OUT VC1-, C1+ V+
_______________________________________________________________________________________
3
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver MAX218
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, VCC = 1.8V, all transmitter outputs loaded with 3k, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
1 TRANSMITTER FULL DATA RATE 1 TRANSMITTER 1/8 DATA RATE RL = 3k + 2500pF 240kbps 80 60 40 20 0 1.8 2.4 3.0 3.6 4.2 SUPPLY VOLTAGE (V) 120kbps 20kbps 0kbps
MAX3218-01
TRANSMITTING SUPPLY CURRENT vs. LOAD CAPACITANCE
VCC = 2.4V 90 SUPPLY CURRENT (mA) 80 70 60 50 40 30 20 0 1000 2000 3000 4000 5000 LOAD CAPACITANCE (pF) 20kbps 120kbps 235kbps TRANSMITTER 1 OPERATING AT SPECIFIED BIT RATE, TRANSMITTER 2 OPERATING AT 1/16 THAT RATE.
MAX3218-02
140 120 SUPPLY CURRENT (mA) 100
100
TIME TO EXIT SHUTDOWN (ONE TRANSMITTER HIGH, ONE TRANSMITTER LOW)
SHDN VOH
2V/div T_OUT
VCC = 1.8V RL = 3k || 2500pF 100s/div
VOL
TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE AT 120kbps
TRANSMITTER OUTPUT VOLTAGE (V) 6 4 2 0 -2 -4 VOUT-6 -8 0 1000 2000 3000 4000 5000 LOAD CAPACITANCE (pF) 0 0 2
MAX3218-04
SLEW RATE vs. TRANSMITTER CAPACITANCE
MAX3218-05
8 VOUT+
12 10 SLEW RATE (V/s) +SLEW 8 6 4 DATA RATE 120kbps, TRANSMITTERS LOADED WITH 3k PLUS INDICATED CAPACITANCE 1000 2000 3000 4000 -SLEW
5000
LOAD CAPACITANCE (pF)
4
_______________________________________________________________________________________
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver MAX218
15H 1 1.8V TO 4.25V 6 1F C4 3 LX VCC D1 1N6050 19 V+ V15 18 16 1F C3 0.47F C1 1F C2
MAX218
ON/OFF SHDN T1
C1+ C1-
The transmitters and receivers are guaranteed to operate at 120kbps data rates, providing compatibility with LapLinkTM and other high-speed communications software. A shutdown mode extends battery life by reducing supply current to 0.04A. While shut down, all receivers can either remain active or be disabled under logic control. With this feature, the MAX218 can be in low-power shutdown mode and still monitor activity on external devices. Three-state drivers are provided on both receiver outputs.
7 T1IN
T1OUT 14
Switch-Mode Power Supply
The switch-mode power supply uses a single inductor with one diode and three small capacitors to generate 6.5V from an input voltage in the 1.8V to 4.25V range.
8 T2IN 9 R1OUT
T2 R1
T2OUT 13 R1IN 12
10 R2OUT EN ENABLE 4
R2 GND
R2IN 11
Inductor Selection Use a 15H inductor with a saturation current rating of at least 350mA and less than 1 resistance. Table 1 lists suppliers of inductors that meet the 15H/350mA/1 specifications. Diode Selection Key diode specifications are fast recovery time (<10ns), average current rating (>100mA), and peak current rating (>350mA). Inexpensive fast silicon diodes, such as the 1N6050, are generally recommended. More expensive Schottky diodes improve efficiency and give slightly better performance at very low VCC voltages. Table 1 lists suppliers of both surface-mount and through-hole diodes. 1N914s are usually satisfactory, but specifications and performance vary widely with different manufacturers. Capacitor Selection Use capacitors with values at least as indicated in Figure 1. Capacitor C2 determines the ripple on V+, but not the absolute voltage. Capacitors C1 and C3 determine both the ripple and the absolute voltage of V-. Bypass VCC to GND with at least 1F (C4) placed close to pins 5 and 6. If the VCC line is not bypassed elsewhere (e.g., at the power supply), increase C4 to 4.7F. You may use ceramic or polarized capacitors in all locations. If you use polarized capacitors, tantalum types are preferred because of the high operating frequency of the power supplies (about 250kHz). If aluminum electrolytics are used, higher capacitance values may be required.
5, 17, 20
Figure 1. Single-Supply Operation
_______________Detailed Description
The MAX218 line driver/receiver is intended for batterypowered EIA/TIA-232 and V.28/V.24 communications interfaces that require two drivers and two receivers. The operating voltage extends from 1.8V to 4.25V, yet the device maintains true RS-232 and EIA/TIA-562 transmitter output voltage levels. This wide supply voltage range permits direct operation from a variety of batteries without the need for a voltage regulator. For example, the MAX218 can be run directly from a single lithium cell or a pair of alkaline cells. It can also be run directly from two NiCd or NiMH cells from full-charge voltage down to the normal 0.9V/cell end-of-life point. The 4.25V maximum supply voltage allows the two rechargeable cells to be trickle- or fast-charged while driving the MAX218. The circuit comprises three sections: power supply, transmitters, and receivers. The power-supply section converts the supplied input voltage to 6.5V, providing the voltages necessary for the drivers to meet true RS-232 levels. External components are small and inexpensive.
TM LapLink is a trademark of Traveling Software, Inc.
_______________________________________________________________________________________ 5
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver MAX218
Table 1. Suggested Component Suppliers
MANUFACTURER Inductors--Surface Mount Murata-Erie Sumida TDK Diodes--Surface Mount Central Semiconductor Motorola Philips Diodes--Through-Hole Motorola 1N6050, Silicon 1N5817, Schottky USA (408) 749-0510 USA (408) 991-7420 CMPSH-3, Schottky MMBD6050LT1, Silicon PMBD6050, Silicon USA (516) 435-1110 USA (408) 749-0510 USA (401) 762-3800 USA (516) 435-1824 USA (408) 991-7420 USA (401) 767-4493 LQH4N150K-TA CD43150 NLC453232T-150K USA (404) 436-1300 Japan (075) 951-9111 USA (708) 956-0666 Japan (03) 3607-5111 USA (708) 803-6100 Japan (03) 3278-5111 USA (404) 436-3030 Japan (075) 955-6526 USA (708) 956-0702 Japan (03) 3607-5428 USA (708) 803-6296 Japan (03) 3278-5358 PART NUMBER PHONE FAX
RS-232 Drivers
The two drivers are identical, and deliver EIA/TIA-232E and EIA/TIA-562 output voltage levels when V DD is between 1.8V and 4.25V. The transmitters drive up to 3k in parallel with 1000pF at up to 120kbps. Connect unused driver inputs-- either GND or VCC. Disable the -- to --- drivers by taking SHDN low. The transmitter-- -- outputs are --- forced into a high-impedance state when SHDN is low.
Shutdown ---- --- When SHDN is low, the power supplies are disabled and the transmitters are put into a high-impedance - ---- -- state. Receiver operation is not affected by taking SHDN low. Power consumption is dramatically reduced in shutdown mode. Supply current is minimized when the receiver inputs are static in any of three states: floating (ground), GND, or VCC.
RS-232 Receivers
The two receivers are identical, and accept both EIA/TIA-232E and EIA/TIA-562 input signals. The CMOS receiver outputs swing rail-to-rail. When EN is high, - -- --the receivers are active regardless of the state of -- SHDN. When EN is low, the receiver outputs are put into a high-impedance state. This allows two RS-232 ports (or two ports of different types) to be wired-ORed at the UART. ---- --- SHDN and EN determine the MAX218's mode of operation, as shown in Table 2.
__________Applications Information
Operation from Regulated/Unregulated Dual System Power Supplies
The MAX218 is intended for use with three different power-supply sources: it can be powered directly from a battery, from a 3.0V or 3.3V power supply, or simultaneously from both. Figure 1 shows the single-supply configuration. Figure 2 shows the circuit for operation from both a 3V supply and a raw battery supply--an ideal configuration where a regulated 3V supply is being derived from two cells. In this application, the MAX218's logic levels remain appropriate for interface with 3V logic, yet most of the power for the MAX218 is drawn directly from the battery, without suffering the efficiency losses of the DC-DC converter. This prolongs battery life. Bypass the input supplies with 0.1F at VCC (C4) and at least 1F at the inductor (C5). Increase C5 to 4.7F if the power supply has no other bypass capacitor connected to it.
Operating Modes
Table 2. Operating Modes
---- ---- RECEIVER DRIVER DC-DC SUPPLY SHDN EN OUTPUT OUTPUT CONVERTER CURRENT L L H H 6 L H L H High-Z Enabled High-Z Enabled High-Z High-Z Enabled Enabled OFF OFF ON ON Minimum Minimum Normal Normal
_______________________________________________________________________________________
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver
15H 3V DC-DC CONVERTER 1F C5 6 0.1F C4 3 SHDN T1 VCC D1 1N6050 1F C2 V+ V15 18 16 1F C3 0.47F C1
1 LX
19
MAX878 OR MAX756 OR MAX856
MAX218
C1+ C1-
ON/OFF
7 T1IN
T1OUT 14
8 T2IN 9 R1OUT
T2 R1
T2OUT 13 R1IN 12
power straight from the battery, but still provides logiclevel compatibility with the 3V logic. Keep communications cables short to minimize capacitive loading. Lowering the capacitive loading on the transmitter outputs reduces the MAX218's power consumption. Using short, low-capacitance cable also helps transmission at the highest data rates. ---- --- Keep the SHDN pin low -- -- power is being applied to while- -- the MAX218, and take SH D N high only after VCC has risen above about 1.5V. This avoids active operation at very low voltages, where currents of up to 150mA can be drawn. This is especially important -- systems pow-- with --- ered from rechargeable cells; if SHDN is high while the cells are being trickle charged from a deep discharge, the MAX218 could draw a significant amount of the charging current until the battery voltage rises above 1.5V.
MAX218
10 R2OUT EN ENABLE 4
R2
R2IN 11 GND 5, 17, 20
Figure 2. Operating from Unregulated and Regulated Supplies
Pin Configuration Change The Pin Configuration shows pin 2 as N.C. (no connect). Early samples had a bypass capacitor for the internal reference connected to pin 2, which was labeled REF. This bypass capacitor proved to be unnecessary and the connection has been omitted. Pin 2 may now be connected to ground, left open, or bypassed to GND with a capacitor.
Low-Power Operation
The following suggestions will help you get maximum life out of your batteries. Shut the MAX218 down when it is not being used for transmission. The receivers can remain active when the MAX218 is shut down, to alert your system to external activity. Transmit at the highest practical data rate. Although this raises the supply current while transmission is in progress, the transmission will be over sooner. As long as the MAX218 is shut down as soon as each transmission ends, this practice will save energy. Operate your whole system from the raw battery voltage rather than suffer the losses of a regulator or DCDC converter. If this is not possible, but your system is powered from two cells and employs a 3V DC-DC converter to generate the main logic supply, use the circuit of Figure 2. This circuit draws most of the MAX218's
EIA/TIA-232E and _____________EIA/TIA-562 Standards
RS-232 circuits consume much of their power because the EIA/TIA-232E standard demands that the transmitters deliver at least 5V to receivers with impedances that can be as low as 3k. For applications where power consumption is critical, the EIA/TIA-562 standard provides an alternative. EIA/TIA-562 transmitter output voltage levels need only reach 3.7V, and because they have to drive the same 3k receiver loads, the total power consumption is considerably reduced. Since the EIA/TIA-232E and EIA/TIA-562 receiver input voltage thresholds are the same, interoperability between EIA/TIA-232E and EIA/TIA-562 devices is guaranteed. Maxim's MAX560 and MAX561 are EIA/TIA-562 transceivers that operate on a single supply from 3.0V to 3.6V, and the MAX562 transceiver operates from 2.7V to 5.25V while producing EIA/TIA-562 levels.
_______________________________________________________________________________________
7
1.8V to 4.25V-Powered, True RS-232 Dual Transceiver MAX218
______3V-Powered EIA/TIA-232 and EIA/TIA-562 Transceivers from Maxim
PART MAX212 MAX3212 MAX218 No. OF SUPPLY No. OF RECEIVERS VOLTAGE TRANSMITTERS/ ACTIVE IN (V) RECEIVERS SHUTDOWN 3.0 to 3.6 2.7 to 3.6 1.8 to 4.25 3/5 3/5 2/2 2/2 4/5 4/5 3/5 2/2 2/2 2/2 2/2 2/2 3/5 5 5 2 2 2 0 5 2 2 2 2 2 1 GUARANTEED DATA RATE (kbps) 120 120 120 120 120 120 230 120 120 120 120 120 120 EIT/TIA232 OR 562 232 232 232 232 562 562 562 562 232 232 232 232 232 Drives mice AutoShutdown, complementary receiver, drives mice, transient detection Operates directly from a battery without a voltage regulator Same as MAX218, but with AutoShutdown Pin-compatible with MAX213 Pin-compatible with MAX214 Wide supply range 0.1F capacitors 0.1F capacitors 0.1F capacitors Pin-compatible with MAX232 0.1F capacitors, 2 complementary receivers, drives mice 0.1F capacitors, AutoShutdown, complementary receivers, drives mice FEATURES
MAX3218 1.8 to 4.25 MAX560 MAX561 MAX562 MAX563 MAX3222 MAX3223 MAX3232 MAX3241 MAX3243 3.0 to 3.6 3.0 to 3.6 2.7 to 5.25 3.0 to 3.6 3.0 to 5.5 3.0 to 5.5 3.0 to 5.5 3.0 to 5.5 3.0 to 5.5
___________________Chip Topography
LX SHDN C1+ EN GND C1V0.101" (2.565mm) GND V+
GND V CC T1IN T2IN R1IN R2OUT R2IN R1OUT 0.122" (3.099mm) T1OUT T2OUT
TRANSISTOR COUNT: 571 SUBSTRATE CONNECTED TO GND
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) 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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