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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 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
PART
TEMP. RANGE
PIN-PACKAGE
MAX218CPP
0°C to +70°C
20 Plastic DIP
MAX218CWP
0°C to +70°C
20 Wide SO
MAX218CAP
0°C to +70°C
20 SSOP
MAX218C/D
0°C to +70°C
Dice*
MAX218EPP
-40°C to +85°C
20 Plastic DIP
MAX218EWP
-40°C to +85°C
20 Wide SO
MAX218EAP
-40°C to +85°C
20 SSOP
*Contact factory for dice specifications.
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
1
19
LX
GND
V+
C1+
GND
1
2
3
4
5
6
7
8
20
19
18
17
16
15
14
13
LX
V+
1.8V
TO
4.25V
15
6
V-
V
CC
N.C.
18
C1+
SHDN
MAX218
3
16
EN
ON/OFF
SHDN
C1-
MAX218
GND
C1-
V-
T1OUT
T2OUT
7
T1IN
T1OUT
14
T1
V
CC
8
T2IN
T2OUT
13
T2
T1IN
9
R1OUT
R1IN
12
T2IN
R1
R1OUT
12
11
R1IN
R2IN
9
10
10
R2OUT
R2IN
11
R2
R2OUT
EN
GND
5,
17, 20
4
ENABLE
DIP/SO/SSOP
________________________________________________________________ Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
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, S
—
H
—
D
—
–
................................................. -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
CONDITIONS
MIN
TYP
MAX
UNITS
DC CHARACTERISTICS
Operating Voltage Range
1.8
4.25
V
No load, V
CC
= EN = S
—
H
—
D
—
–
= 3.0V, T
A
= +25°C
Supply Current (Note 1)
1.9
3.0
mA
S
—
H
—
D
—
–
= EN = 0V, all R_INs static
S
—
H
—
D
—
–
= 0V, EN = V
CC
, all R_INs static
0.04
10
Shutdown Supply Current
µA
0.04
10
LOGIC
T_IN, EN, S
—
H
—
D
—
–
Input Logic Threshold Low
0.33 x V
CC
V
T_IN, EN, S
—
H
—
D
—
–
Input Logic Threshold High
0.67 x V
CC
V
Input Hysteresis
T_IN
0.1
V
T_IN, EN, S
—
H
—
D
—
–
= 0V or V
CC
Input Leakage Current
0.001
±1
µA
Output Voltage Low
R_OUT, I
OUT
= 1.0mA
0.4
V
Output Voltage High
R_OUT, I
OUT
= -0.4mA
V
CC
- 0.25
V
CC
- 0.08
V
Output Leakage Current
R_OUT, 0V
²
R_OUT
²
V
CC
, EN = 0V
0.05
±10
µA
EIA/TIA-232E RECEIVER INPUTS
Input Voltage Range
-25
+25
V
V
CC
= 2.0V to 4.25V
0.4
Input Threshold Low
V
V
CC
= 1.8V to 4.25V
0.3
V
CC
= 1.8V to 4.25V
3.0
Input Threshold High
V
V
CC
= 1.8V to 3.6V
2.8
Input Hysteresis
0.7
V
Input Resistance
-15V < R_IN < +15V
3
5
7
k
½
EIA/TIA-232E TRANSMITTER OUTPUTS
Output Voltage Swing
All transmitter outputs loaded with 3k
½
to ground
±5
±6
V
Output Resistance
V
CC
= 0V, -2V < T_OUT < +2V
300
½
Output Short-Circuit Current
±24
±100
mA
Note 1:
Entire supply current for the circuit of Figure 1.
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
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
1000pF
||
3k
½
load each transmitter,
150pF load each receiver
Data Rate
120
kbps
Receiver Output Enable Time
t
ER
90
300
ns
Receiver Output Disable Time
t
DR
200
500
ns
Transmitter Output Enable Time
t
ET
140
450
µs
Transmitter Output Disable Time
t
DT
500
ns
t
PHLR
150pF load
150pF load
2500pF
||
3k
½
290
700
Receiver Propagation Delay
ns
t
PLHR
260
700
t
PHLT
load
1.9
2.7
Transmitter Propagation Delay
µs
2500pF
||
3k
½
t
PLHT
1.8
2.7
load
T
A
= +25°C, V
CC
= 3.0V, R
L
= 3k
½
to 7k
½
,
Transition Region Slew Rate
C
L
= 50pF to 2500pF, measured from
+3V to -3V or -3V to +3V
3.0
30
V/µs
______________________________________________________________Pin Description
PIN
NAME
FUNCTION
1
LX
Inductor/Diode Connection Point
2
N.C.
Not internally connected
S
—
H
—
D
—
–
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.
3
Receiver Output Enable Control. Connect to V
CC
for normal operation. Connect to GND to
force the receiver outputs into high-Z state.
4
EN
5, 17, 20
GND
Ground. Connect all GND pins to ground.
Supply Voltage Input; 1.8V to 4.25V. Bypass to GND with at least 1µF. See Capacitor
Selectionsection.
6
V
CC
7, 8
T1IN, T2IN
Transmitter Inputs
9, 10
R1OUT, R2OUT
Receiver Outputs; swing between GND and V
CC.
11, 12
R2IN, R1IN
Receiver Inputs
13, 14
T2OUT, T1OUT
Transmitter Outputs; swing between V+ and V-.
15
V-
Negative Supply generated on-board
16, 18
C1-, C1+
Terminals for Negative Charge-Pump Capacitor
19
V+
Positive Supply generated on-board
_______________________________________________________________________________________
3
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, V
CC
= 1.8V, all transmitter outputs loaded with 3k
½
, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs.
SUPPLY VOLTAGE
TRANSMITTING SUPPLY CURRENT
vs. LOAD CAPACITANCE
140
100
1 TRANSMITTER FULL DATA RATE
1 TRANSMITTER 1/8 DATA RATE
R
L
= 3k
W
+ 2500pF
V
CC
= 2.4V
90
80
70
120
235kbps
100
TRANSMITTER 1 OPERATING
AT SPECIFIED BIT RATE,
TRANSMITTER 2 OPERATING
AT 1/16 THAT RATE.
240kbps
80
60
50
60
120kbps
20kbps
120kbps
40
20
40
20kbps
0kbps
30
0
20
0
1000
2000
3000
4000
5000
1.8
2.4
3.0
3.6
4.2
SUPPLY VOLTAGE (V)
LOAD CAPACITANCE (pF)
TIME TO EXIT SHUTDOWN
(ONE TRANSMITTER HIGH,
ONE TRANSMITTER LOW)
SHDN
V
OH
2V/div
T_OUT
V
CC =
1.8V
R
L
= 3k
W
|| 2500pF
V
OL
100
m
s/div
SLEW RATE vs.
TRANSMITTER CAPACITANCE
TRANSMITTER OUTPUT VOLTAGE vs.
LOAD CAPACITANCE AT 120kbps
12
8
6
4
2
10
V
OUT+
+SLEW
8
-SLEW
6
0
-2
4
DATA RATE 120kbps,
TRANSMITTERS LOADED WITH
3k
W
PLUS INDICATED CAPACITANCE
-4
V
OUT-
2
-6
0
-8
1000
0
1000
2000
3000
4000
5000
0
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
LOAD CAPACITANCE (pF)
4
_______________________________________________________________________________________
1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver
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.
D1
1N6050
15
m
H
1
m
F
C2
19
1
V+
LX
1.8V
TO
4.25V
6
15
V-
V
CC
1
m
F
C3
1
m
F
C4
18
C1+
MAX218
0.47
m
F
3
16
C1
ON/OFF
SHDN
C1-
T1IN
T1OUT
7
14
T1
8
T2IN
T2OUT
13
T2
R1OUT
9
R1IN
12
R1
Inductor Selection
Use a 15µH inductor with a saturation current rating of at
least 350mA and less than 1
½
resistance. Table 1 lists
suppliers of inductors that meet the 15µH/350mA/1
½
specifications.
10
R2OUT
R2IN
11
R2
EN
GND
4
5,
17, 20
ENABLE
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.
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.
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.
™ LapLink is a trademark of Traveling Software, Inc.
_______________________________________________________________________________________
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