_______________General Description
The MAX218 RS-232 transceiver is intended for battery-
powered 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
1µA, extending battery life in portable systems. While
shut down, all receivers can remain active or can be
disabled under logic control, permitting a system incor-
porating 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.
________________________Applications
Battery-Powered Equipment
Computers
Printers
Peripherals
Instruments
Modems
____________________________Features
BETTER THAN BIPOLAR!
♦Operates Directly from Two Alkaline, NiCd,
or NiMH Cells
♦+1.8V to +4.25V Supply Voltage Range
♦120kbps Data Rate
♦Low-Cost Surface-Mount Components
♦Meets EIA/TIA-232E Specifications
♦1µA Low-Power Shutdown Mode
♦Both Receivers Active During Low-Power Shutdown
♦Three-State Receiver Outputs
♦Flow-Through Pinout
♦On-Board DC-DC Converters
♦20-Pin SSOP, Wide SO, or DIP Packages
______________Ordering Information
*Contact factory for dice specifications.
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
________________________________________________________________
Maxim Integrated Products
1
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
GND
V+
C1+
GND
EN
SHDN
N.C.
LX
TOP VIEW
C1-
V-
T1OUT
T2OUT
T2IN
T1IN
VCC
GND
12
11
9
10
R1IN
R2IN
R2OUT
R1OUT
DIP/SO/SSOP
MAX218
__________________Pin Configuration
R1
R2
T1
T2
T1OUT
T2OUT
T1IN
T2IN
R1OUT
R2OUT
R1IN
R2IN
GND
EN
VCC
SHDN
LX
C1+
C1-
V-
6
3
7
8
9
10 11
12
13
14
16
18
15
45, 17, 20
MAX218
ENABLE
ON/OFF
1.8V
TO
4.25V
1V+
19
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0246; Rev 1; 7/95
PART TEMP. RANGE
MAX218CPP 0°C to +70°C
MAX218C/D 0°C to +70°C Dice*
20 Plastic DIP
PIN-PACKAGE
MAX218CAP 0°C to +70°C 20 SSOP
MAX218EPP -40°C to +85°C
MAX218EAP -40°C to +85°C 20 SSOP
20 Plastic DIP
MAX218EWP -40°C to +85°C 20 Wide SO
MAX218CWP 0°C to +70°C 20 Wide SO
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VCC = 1.8V to 4.25V, C1 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, TA= TMIN to TMAX, unless otherwise noted.
Typical values are at VCC = 3.0V, 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.
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, S
—
H
—
D
—
N
–................................................. -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= +70°C)
Plastic DIP (derate 11.11mW/°C above +70°C) ..........889mW
Wide SO (derate 10.00mW/°C above +70°C)..............800mW
SSOP (derate 8.00mW/°C above +70°C) ...................640mW
Operating Temperature Ranges
MAX218C_ P..................................................... 0°C to +70°C
MAX218E_ P................................................... -40°C to +85°C
Storage Temperature Range ........................... -65°C to +150°C
Lead Temperature (soldering, 10sec) ........................... +300°C
All transmitter outputs loaded with 3kΩto ground
-15V < R_IN < +15V
No load, VCC = EN = S
—
H
—
D
—
N
–= 3.0V, TA= +25°C
VCC = 1.8V to 3.6V
VCC = 1.8V to 4.25V
VCC = 1.8V to 4.25V
VCC = 2.0V to 4.25V
R_OUT, IOUT = 1.0mA
T_IN, EN, S
—
H
—
D
—
N
–= 0V or VCC
T_IN
T_IN, EN, S
—
H
—
D
—
N
–
S
—
H
—
D
—
N
–= EN = 0V, all R_INs static
S
—
H
—
D
—
N
–= 0V, EN = VCC, all R_INs static
R_OUT, 0V ≤R_OUT ≤VCC, EN = 0V
T_IN, EN, S
—
H
—
D
—
N
–
R_OUT, IOUT = -0.4mA
CONDITIONS
V±5 ±6Output Voltage Swing
kΩ357Input Resistance V0.7Input Hysteresis
V
2.8
Input Threshold High 3.0
V
0.3
Input Threshold Low 0.4 V-25 +25Input Voltage Range
µA0.05 ±10Output Leakage Current VVCC - 0.25 VCC - 0.08Output Voltage High
mA1.9 3.0Supply Current (Note 1) V1.8 4.25Operating Voltage Range
V0.4Output Voltage Low µA0.001 ±1Input Leakage Current V0.1Input Hysteresis V0.67 x VCC
Input Logic Threshold High
0.04 10 µA
0.04 10
Shutdown Supply Current
V0.33 x VCC
Input Logic Threshold Low
UNITSMIN TYP MAXPARAMETER
VCC = 0V, -2V < T_OUT < +2V mA±24 ±100Output Short-Circuit Current Ω300Output Resistance
DC CHARACTERISTICS
EIA/TIA-232E RECEIVER INPUTS
LOGIC
EIA/TIA-232E TRANSMITTER OUTPUTS
Note 1: Entire supply current for the circuit of Figure 1.
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
_______________________________________________________________________________________ 3
TIMING CHARACTERISTICS
(Circuit of Figure 1, VCC = 1.8V to 4.25V, C1 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, TA= TMIN to TMAX, unless otherwise noted.
Typical values are at VCC = 3.0V, TA= +25°C.)
1000pF || 3kΩload each transmitter,
150pF load each receiver
TA= +25°C, VCC = 3.0V, RL= 3kΩto 7kΩ,
CL= 50pF to 2500pF, measured from
+3V to -3V or -3V to +3V
2500pF || 3kΩload
150pF load
150pF load
2500pF || 3kΩload
CONDITIONS
ns200 500tDR
Receiver Output Disable Time ns90 300tER
kbps120Data Rate
Receiver Output Enable Time
V/µs3.0 30Transition Region Slew Rate
1.8 2.7tPLHT
Transmitter Propagation Delay
µs140 450tET
Transmitter Output Enable Time
ns
290 700tPHLR 260 700tPLHR
Receiver Propagation Delay
µs
1.9 2.7tPHLT
UNITS
MIN TYP MAX
SYMBOLPARAMETER
ns500tDT
Transmitter Output Disable Time
______________________________________________________________Pin Description
Receiver InputsR2IN, R1IN11, 12
Transmitter Outputs; swing between V+ and V-.T2OUT, T1OUT13, 14
Negative Supply generated on-boardV-15
Terminals for Negative Charge-Pump CapacitorC1-, C1+16, 18
Positive Supply generated on-boardV+19
Ground. Connect all GND pins to ground.GND5, 17, 20
Supply Voltage Input; 1.8V to 4.25V. Bypass to GND with at least 1µF. See
Capacitor
Selection
section.
VCC
6
Transmitter InputsT1IN, T2IN7, 8
Receiver Outputs; swing between GND and VCC.
R1OUT, R2OUT9, 10
Receiver Output Enable Control. Connect to VCC for normal operation. Connect to GND to
force the receiver outputs into high-Z state.
EN4
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.
S
—
H
—
D
—
N
–
3
PIN
Not internally connectedN.C.2
Inductor/Diode Connection PointLX1
FUNCTIONNAME
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
4 _______________________________________________________________________________________
8
-8 0
TRANSMITTER OUTPUT VOLTAGE vs.
LOAD CAPACITANCE AT 120kbps
MAX3218-04
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
3000
0
-2
-6
-4
1000 2000 5000
6
4
2
4000
VOUT+
VOUT-
12
0
SLEW RATE vs.
TRANSMITTER CAPACITANCE
MAX3218-05
LOAD CAPACITANCE (pF)
SLEW RATE (V/µs)
3000
4
2
01000 2000 5000
10
8
6
4000
+SLEW
-SLEW
DATA RATE 120kbps,
TRANSMITTERS LOADED WITH
3kΩ PLUS INDICATED CAPACITANCE
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, VCC = 1.8V, all transmitter outputs loaded with 3kΩ, TA = +25°C, unless otherwise noted.)
120
140
01.8
SUPPLY CURRENT vs.
SUPPLY VOLTAGE
MAX3218-01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.6
60
40
20
2.4 3.0
80
100
4.2
1 TRANSMITTER FULL DATA RATE
1 TRANSMITTER 1/8 DATA RATE
RL = 3kΩ + 2500pF
240kbps
120kbps
20kbps
0kbps
100
20 0
TRANSMITTING SUPPLY CURRENT
vs. LOAD CAPACITANCE
MAX3218-02
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
3000
60
50
30
40
1000 2000 5000
90
80
70
4000
20kbps
120kbps
VCC = 2.4V
TRANSMITTER 1 OPERATING
AT SPECIFIED BIT RATE,
TRANSMITTER 2 OPERATING
AT 1/16 THAT RATE.
235kbps
VOH
SHDN
T_OUT
2V/div
VOL
TIME TO EXIT SHUTDOWN
(ONE TRANSMITTER HIGH,
ONE TRANSMITTER LOW)
100µs/div
VCC = 1.8V
RL = 3kΩ || 2500pF
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
_______________________________________________________________________________________ 5
_______________Detailed Description
The MAX218 line driver/receiver is intended for battery-
powered 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 volt-
age 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.
The transmitters and receivers are guaranteed to oper-
ate at 120kbps data rates, providing compatibility with
LapLink™ and other high-speed communications soft-
ware. A shutdown mode extends battery life by reduc-
ing supply current to 0.04µA. 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.
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.
Inductor Selection
Use a 15µH inductor with a saturation current rating of at
least 350mA and less than 1Ωresistance. Table 1 lists
suppliers of inductors that meet the 15µH/350mA/1Ω
specifications.
Diode Selection
Key diode specifications are fast recovery time (<10ns),
average current rating (>100mA), and peak current rat-
ing (>350mA). Inexpensive fast silicon diodes, such as
the 1N6050, are generally recommended. More expen-
sive 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 specifica-
tions and performance vary widely with different manu-
facturers.
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 1µF (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
4.7µF.
You may use ceramic or polarized capacitors in all
locations. If you use polarized capacitors, tantalum
types are preferred because of the high operating fre-
quency of the power supplies (about 250kHz). If alu-
minum electrolytics are used, higher capacitance val-
ues may be required.
™ LapLink is a trademark of Traveling Software, Inc.
R1
R2
T1
T2
T1OUT
T2OUT
T1IN
T2IN
R1OUT
R2OUT
R1IN
R2IN
GND
EN
VCC
SHDN
LX
C1+
C1-
V-
6
3
7
8
9
10 11
12
13
14
16
18
15
45, 17, 20
MAX218
ENABLE
ON/OFF
1.8V
TO
4.25V
1V+
19
1µF
C4
1µF
C2
1µF
C3
0.47µF
C1
15µHD1
1N6050
Figure 1. Single-Supply Operation
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
6 _______________________________________________________________________________________
RS-232 Drivers
The two drivers are identical, and deliver EIA/TIA-232E
and EIA/TIA-562 output voltage levels when VDD is
between 1.8V and 4.25V. The transmitters drive up to
3kΩin parallel with 1000pF at up to 120kbps. Connect
unused driver inputs to either GND or VCC. Disable the
drivers by taking S
—
H
—
D
—
N
–low. The transmitter outputs are
forced into a high-impedance state when S
—
H
—
D
—
N
–is low.
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
S
—
H
—
D
—
N
–. 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.
Operating Modes
S
—
H
—
D
—
N
–and EN determine the MAX218’s mode of opera-
tion, as shown in Table 2.
Table 2. Operating Modes
Shutdown
When S
—
H
—
D
—
N
–is low, the power supplies are disabled and
the transmitters are put into a high-impedance state.
Receiver operation is not affected by taking S
—
H
—
D
—
N
–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.
__________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 simulta-
neously 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 pro-
longs battery life.
Bypass the input supplies with 0.1µF at VCC (C4) and at
least 1µF at the inductor (C5). Increase C5 to 4.7µF if
the power supply has no other bypass capacitor con-
nected to it.
MANUFACTURER PART NUMBER PHONE FAX
Murata-Erie LQH4N150K-TA USA (404) 436-1300
Japan (075) 951-9111 USA (404) 436-3030
Japan (075) 955-6526
Sumida CD43150 USA (708) 956-0666
Japan (03) 3607-5111 USA (708) 956-0702
Japan (03) 3607-5428
TDK NLC453232T-150K USA (708) 803-6100
Japan (03) 3278-5111 USA (708) 803-6296
Japan (03) 3278-5358
Central Semiconductor CMPSH-3, Schottky USA (516) 435-1110 USA (516) 435-1824
Motorola MMBD6050LT1, Silicon USA (408) 749-0510 USA (408) 991-7420
Philips PMBD6050, Silicon USA (401) 762-3800 USA (401) 767-4493
Motorola 1N6050, Silicon
1N5817, Schottky USA (408) 749-0510 USA (408) 991-7420
Table 1. Suggested Component Suppliers
–
S
—
H
—
D
—
N
–EN RECEIVER
OUTPUT DRIVER
OUTPUT DC-DC
CONVERTER
L L High-Z High-Z OFF
L H Enabled High-Z OFF
H L High-Z Enabled ON
H H Enabled Enabled ON
SUPPLY
CURRENT
Minimum
Minimum
Normal
Normal
Inductors—Surface Mount
Diodes—Surface Mount
Diodes—Through-Hole
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
_______________________________________________________________________________________ 7
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 exter-
nal 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 transmis-
sion ends, this practice will save energy.
Operate your whole system from the raw battery volt-
age rather than suffer the losses of a regulator or DC-
DC converter. If this is not possible, but your system is
powered from two cells and employs a 3V DC-DC con-
verter to generate the main logic supply, use the circuit
of Figure 2. This circuit draws most of the MAX218’s
power straight from the battery, but still provides logic-
level compatibility with the 3V logic.
Keep communications cables short to minimize capaci-
tive loading. Lowering the capacitive loading on the
transmitter outputs reduces the MAX218’s power con-
sumption. Using short, low-capacitance cable also
helps transmission at the highest data rates.
Keep the S
—
H
—
D
—
N
–pin low while power is being applied to
the MAX218, and take S
—
H
—
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 with systems pow-
ered from rechargeable cells; if S
—
H
—
D
—
N
–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.
Pin Configuration Change
The
Pin Configuration
shows pin 2 as N.C. (no con-
nect). 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.
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 transmit-
ters deliver at least 5V to receivers with impedances
that can be as low as 3kΩ. 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
3kΩreceiver loads, the total power consumption is con-
siderably 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 produc-
ing EIA/TIA-562 levels.
R1
R2
T1
T2
T1OUT
T2OUT
T1IN
T2IN
R1OUT
R2OUT
R1IN
R2IN
GND
EN
VCC
SHDN
LX
C1+
C1-
V-
6
3
7
8
9
10 11
12
13
14
16
18
15
45, 17, 20
MAX218
ENABLE
ON/OFF
1V+
19
0.1µF
C4
1µF
C5
1µF
C2
1µF
C3
0.47µF
C1
15µHD1
1N6050
3V
DC-DC
CONVERTER
MAX878
OR
MAX756
OR
MAX856
Figure 2. Operating from Unregulated and Regulated Supplies
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
© 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX218
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
___________________Chip Topography
TRANSISTOR COUNT: 571
SUBSTRATE CONNECTED TO GND
C1+
GND
T1OUT
SHDN
EN
T2OUT
GND
T1IN
LX V+
R2IN
R1OUT
T2IN R2OUT
0.101"
(2.565mm)
0.122"
(3.099mm)
R1IN
C1-
V-
GND
VCC
______3V-Powered EIA/TIA-232 and EIA/TIA-562 Transceivers from Maxim
0.1µF capacitors, AutoShutdown,
complementary receivers, drives mice
23212013/53.0 to 5.5MAX3243
0.1µF capacitors, 2 complementary
receivers, drives mice
23212022/23.0 to 5.5MAX3241
Pin-compatible with MAX23223212022/23.0 to 5.5MAX3232 0.1µF capacitors23212022/23.0 to 5.5MAX3223 0.1µF capacitors23212022/23.0 to 5.5MAX3222
Same as MAX218, but with AutoShutdown23212022/21.8 to 4.25MAX3218
AutoShutdown, complementary receiver,
drives mice, transient detection
23212053/52.7 to 3.6MAX3212
0.1µF capacitors56212022/23.0 to 3.6MAX563 Wide supply range56223053/52.7 to 5.25MAX562 Pin-compatible with MAX21456212004/53.0 to 3.6MAX561 Pin-compatible with MAX21356212024/53.0 to 3.6MAX560
Operates directly from a battery
without a voltage regulator
23212022/21.8 to 4.25MAX218
Drives mice23212053/53.0 to 3.6MAX212
FEATURES
EIT/TIA-
232
OR 562
GUARANTEED
DATA RATE
(kbps)
No. OF
RECEIVERS
ACTIVE IN
SHUTDOWN
No. OF
TRANSMITTERS/
RECEIVERS
SUPPLY
VOLTAGE
(V)
PART
