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 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.
____________________________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
1µA 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
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
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
V
CC
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
V
CC
6
ON/OFF
3
MAX218
SHDN
T1
T2
R1
R2
4
C1+ 18
C1-
16
7 T1IN
8 T2IN
9 R1OUT
10 R2OUT
EN
ENABLE
T1OUT 14
T2OUT 13
R1IN 12
R2IN 11
GND
5, 17, 20
MAX218
16 C1-
15 V-
14 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
V
CC
....................................................................-0.3V to +4.6V
V+ .......................................................... (V
CC
- 0.3V) to +7.5V
V- .......................................................................+0.3V to -7.4V
V
CC
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 (V
CC
+ 0.3V)
Short-Circuit Duration, R_OUT, T_OUT to GND ....... Continuous
Continuous Power Dissipation (T
A
= +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
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, V
CC
= 1.8V to 4.25V, C1 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, T
A
= T
MIN
to T
MAX
, unless otherwise noted.
Typical values are at V
CC
= 3.0V, T
A
= +25°C.)
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 3kΩ to ground
V
CC
= 0V, -2V < T_OUT < +2V
3
±5
300
±24
±100
EIA/TIA-232E TRANSMITTER OUTPUTS
±6
V
Ω
mA
V
CC
= 2.0V to 4.25V
V
CC
= 1.8V to 4.25V
V
CC
= 1.8V to 4.25V
V
CC
= 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 V
CC
R_OUT, I
OUT
= 1.0mA
R_OUT, I
OUT
= -0.4mA
R_OUT, 0V
≤
R_OUT
≤
V
CC
, EN = 0V
-25
0.4
0.3
3.0
2.8
V
CC
- 0.25
V
CC
- 0.08
0.05
±10
+25
0.33 x V
CC
0.67 x V
CC
0.1
0.001
±1
0.4
V
V
V
µA
V
V
µA
V
V
V
V
kΩ
— —
— –
No load, V
CC
= EN = SHDN = 3.0V, T
A
= +25°C
— —
— –
SHDN = EN = 0V, all R_INs static
— —
— –
SHDN = 0V, EN = V
CC
, all R_INs static
1.8
1.9
0.04
0.04
4.25
3.0
10
10
V
mA
µA
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, V
CC
= 1.8V to 4.25V, C1 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, T
A
= T
MIN
to T
MAX
, unless otherwise noted.
Typical values are at V
CC
= 3.0V, T
A
= +25°C.)
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
t
ER
t
DR
t
ET
t
DT
t
PHLR
t
PLHR
t
PHLT
t
PLHT
150pF load
150pF load
2500pF
||
3kΩ load
2500pF
||
3kΩ load
T
A
= +25°C, V
CC
= 3.0V, R
L
= 3kΩ to 7kΩ,
C
L
= 50pF to 2500pF, measured from
+3V to -3V or -3V to +3V
3.0
SYMBOL
CONDITIONS
1000pF
||
3kΩ 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
µs
ns
ns
µs
MAX218
Transition Region Slew Rate
V/µs
______________________________________________________________Pin Description
PIN
1
2
3
NAME
LX
N.C.
— —
— –
SHDN
Inductor/Diode Connection Point
Not internally connected
Shutdown Control. Connect to V
CC
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 V
CC
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 1µF. See
Capacitor
Selection
section.
Transmitter Inputs
Receiver Outputs; swing between GND and V
CC.
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
V
CC
T1IN, T2IN
R1OUT, R2OUT
R2IN, R1IN
T2OUT, T1OUT
V-
C1-, C1+
V+
_______________________________________________________________________________________
3
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
MAX218
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, V
CC
= 1.8V, all transmitter outputs loaded with 3kΩ, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs.
SUPPLY VOLTAGE
1 TRANSMITTER FULL DATA RATE
1 TRANSMITTER 1/8 DATA RATE
R
L
= 3kΩ + 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
V
CC
= 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
V
OH
2V/div
T_OUT
V
CC =
1.8V
R
L
= 3kΩ || 2500pF
100µs/div
V
OL
TRANSMITTER OUTPUT VOLTAGE vs.
LOAD CAPACITANCE AT 120kbps
TRANSMITTER OUTPUT VOLTAGE (V)
6
4
2
0
-2
-4
V
OUT-
-6
-8
0
1000
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
0
0
2
MAX3218-04
SLEW RATE vs.
TRANSMITTER CAPACITANCE
MAX3218-05
8
V
OUT+
12
10
SLEW RATE (V/µs)
+SLEW
8
6
4
DATA RATE 120kbps,
TRANSMITTERS LOADED WITH
3kΩ 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
15µH
1
1.8V
TO
4.25V
6
1µF
C4
3
LX
V
CC
D1
1N6050
19
V+
V-
15
18
16
1µF
C3
0.47µF
C1
1µF
C2
MAX218
ON/OFF
SHDN
T1
C1+
C1-
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.
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 15µH inductor with a saturation current rating of at
least 350mA and less than 1Ω resistance. 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 V
CC
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 V
CC
to GND with at least 1µF (C4) placed
close to pins 5 and 6. If the V
CC
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.
5, 17, 20
Figure 1. Single-Supply Operation
_______________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.
™ LapLink is a trademark of Traveling Software, Inc.
_______________________________________________________________________________________
5
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