Maxim MAX218CWP, MAX218CPP, MAX218CAP, MAX218EAP, MAX218C-D Datasheet

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
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 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.

________________________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

MAX218CPP 0°C to +70°C
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
MAX218EWP -40°C to +85°C 20 Wide SO
MAX218EAP -40°C to +85°C 20 SSOP

*Contact factory for dice specifications.

PIN-PACKAGE

20 Plastic DIP

20 Plastic DIP

MAX218

__________Typical Operating Circuit

1

19

V+

1.8V

4.25V

ON/OFF

ENABLE

TO

LX

6

V

CC

MAX218

3

SHDN
T1IN

7

8
9

10

________________________________________________________________

T2IN
R1OUT

R2OUT

T1

T2

R1

R2

EN

4

GND

C1+

C1-

T1OUT

T2OUT

R1IN

R2IN

5, 17, 20

15

V-

18
16

14

13
12

11

__________________Pin Configuration

TOP VIEW

N.C.

SHDN

GND

V
T1IN
T2IN

R1OUT
R2OUT

LX

1
2
3

EN

4
5
6

CC

7
8
9

10

MAX218

DIP/SO/SSOP

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

GND

20

V+

19

C1+

18

GND

17

C1-

16

V-

15

T1OUT

14

T2OUT

13

R1IN

12

R2IN

11

1

1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver

ABSOLUTE MAXIMUM RATINGS

Supply Voltages

....................................................................-0.3V to +4.6V

V

CC

V+.......................................................... (V

V-.......................................................................+0.3V to -7.4V

to V-..........................................................................+12V

V

CC

LX ................................................................-0.3V to (1V + V+)

Input Voltages

MAX218

T_IN, EN, S—H—D—N–................................................. -0.3V to +7V

R_IN.................................................................................±25V

Output Voltages

T_OUT.............................................................................±15V)

R_OUT....................................................-0.3V to (V

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.

- 0.3V) to +7.5V

CC

CC

+ 0.3V)

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VCC= 1.8V to 4.25V, C1 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, TA= T
Typical values are at V

DC CHARACTERISTICS

Shutdown Supply Current

LOGIC

Input Logic Threshold Low
Input Logic Threshold High

EIA/TIA-232E RECEIVER INPUTS

Input Threshold Low

Input Threshold High

EIA/TIA-232E TRANSMITTER OUTPUTS

Note 1: Entire supply current for the circuit of Figure 1.

= 3.0V, TA= +25°C.)

CC

No load, VCC= EN = S—H—D—N–= 3.0V, TA= +25°C
S—H—D—N–= EN = 0V, all R_INs static
S—H—D—N–= 0V, EN = VCC, all R_INs static

T_IN, EN, S—H—D—N
T_IN, EN, S—H—D—N
T_IN
T_IN, EN, S—H—D—N–= 0V or V
R_OUT, I
R_OUT, I
R_OUT, 0V ≤ R_OUT ≤ VCC, EN = 0V

VCC= 2.0V to 4.25V
VCC= 1.8V to 4.25V
VCC= 1.8V to 4.25V
VCC= 1.8V to 3.6V

-15V < R_IN < +15V

All transmitter outputs loaded with 3kΩ to ground
VCC= 0V, -2V < T_OUT < +2V

OUT
OUT

CONDITIONS

–
–

CC

= 1.0mA

= -0.4mA

Short-Circuit Duration, R_OUT, T_OUT to GND ....... Continuous

Continuous Power Dissipation (T

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

CC

0.4

0.3

= +70°C)

A

to T

MIN

MAX

0.04 10

0.04 10

, unless otherwise noted.

UNITSMIN TYP MAXPARAMETER

CC

3.0

2.8

V1.8 4.25Operating Voltage Range

mA1.9 3.0Supply Current (Note 1)

µA

V0.33 x V
V0.67 x V
V0.1Input Hysteresis

µA0.001 ±1Input Leakage Current

V0.4Output Voltage Low
VVCC- 0.25 VCC- 0.08Output Voltage High

µA0.05 ±10Output Leakage Current

V-25 +25Input Voltage Range
V

V
V0.7Input Hysteresis

kΩ357Input Resistance

V±5 ±6Output Voltage Swing
Ω300Output Resistance

mA±24 ±100Output Short-Circuit Current

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 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, TA= T
Typical values are at V

Receiver Output Enable Time
Receiver Output Disable Time
Transmitter Output Enable Time
Transmitter Output Disable Time

Receiver Propagation Delay

Transmitter Propagation Delay

= 3.0V, TA= +25°C.)

CC

SYMBOLPARAMETER

CONDITIONS

1000pF || 3kΩ load each transmitter,
150pF load each receiver

ER
DR
ET
DT

150pF load

PHLR

150pF load

PLHR

2500pF || 3kΩ load

PHLT

2500pF || 3kΩ load

PLHT

TA= +25°C, VCC= 3.0V, RL= 3kΩ to 7kΩ,
CL= 50pF to 2500pF, measured from
+3V to -3V or -3V to +3V

to T

MIN

MIN TYP MAX

, unless otherwise noted.

MAX

290 700t
260 700t

1.9 2.7t

1.8 2.7t

UNITS

kbps120Data Rate

ns90 300t
ns200 500t
µs140 450t
ns500t

ns

µs

V/µs3.0 30Transition Region Slew Rate

______________________________________________________________Pin Description

PIN

Inductor/Diode Connection PointLX1
Not internally connectedN.C.2

–

3

6

S—H—D—N

EN4

V

CC

R1OUT, R2OUT9, 10

Shutdown Control. Connect to VCCfor 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 VCCfor normal operation. Connect to GND to
force the receiver outputs into high-Z state.

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

Selection

Transmitter InputsT1IN, T2IN7, 8
Receiver Outputs; swing between GND and V
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

section.

FUNCTIONNAME

Capacitor

CC.

MAX218

_______________________________________________________________________________________ 3

1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver

__________________________________________Typical Operating Characteristics

(Circuit of Figure 1, VCC= 1.8V, all transmitter outputs loaded with 3kΩ, TA = +25°C, unless otherwise noted.)

140

MAX218

120

100

80

60

40

SUPPLY CURRENT (mA)

20

0

SUPPLY CURRENT vs.

SUPPLY VOLTAGE

1 TRANSMITTER FULL DATA RATE
1 TRANSMITTER 1/8 DATA RATE
RL = 3kΩ + 2500pF

240kbps

120kbps

20kbps

0kbps

1.8

2.4 3.0

SUPPLY VOLTAGE (V)

TRANSMITTING SUPPLY CURRENT

100

MAX3218-01

3.6

4.2

90
80
70
60
50

SUPPLY CURRENT (mA)

40
30

20

vs. LOAD CAPACITANCE

VCC = 2.4V

235kbps

TRANSMITTER 1 OPERATING 
AT SPECIFIED BIT RATE, 
TRANSMITTER 2 OPERATING 
AT 1/16 THAT RATE.


120kbps

20kbps

1000

0

LOAD CAPACITANCE (pF)

2000

3000

4000

MAX3218-02

5000

TIME TO EXIT SHUTDOWN

(ONE TRANSMITTER HIGH,

ONE TRANSMITTER LOW)

SHDN

V

OH

2V/div

V

1.8V

CC =

= 3kΩ || 2500pF

R

L

100µs/div

T_OUT

V

OL

TRANSMITTER OUTPUT VOLTAGE vs. 

LOAD CAPACITANCE AT 120kbps

8
6
4
2

0

-2

-4

TRANSMITTER OUTPUT VOLTAGE (V)

-6

-8
1000

0

LOAD CAPACITANCE (pF)

2000

3000

V

V

OUT+

OUT-

4000

5000

MAX3218-04

12

10

8

6

4

SLEW RATE (V/µs)

2

0

0

SLEW RATE vs.

TRANSMITTER CAPACITANCE

+SLEW

-SLEW

DATA RATE 120kbps,
TRANSMITTERS LOADED WITH 
3kΩ PLUS INDICATED CAPACITANCE


1000

2000

LOAD CAPACITANCE (pF)

3000

4 _______________________________________________________________________________________

4000

MAX3218-05

5000

1.8V to 4.25V-Powered,

True RS-232 Dual Transceiver

D1

15µH

1.8V
TO

4.25V

ON/OFF

ENABLE

Figure 1. Single-Supply Operation

1µF
C4

6

V

3

SHDN

T1IN

7

T2IN

8

R1OUT

9

R2OUT

10

1N6050

C1+

C1-

1µF

C2

15

V-

1µF

C3

18

0.47µF

16

C1

14

13

12

11

19

1

LX

CC

EN

4

MAX218

T1

T2

R1

R2

V+

T1OUT

T2OUT

R1IN

R2IN

GND

5, 17, 20

_______________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.

The transmitters and receivers are guaranteed to oper­ate at 120kbps data rates, providing compatibility with
LapLink™ and other high-speed communications soft­ware. A shutdown mode extends battery life by reduc­ing 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 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 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 VCCvoltages. 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 VCCto GND with at least 1µF (C4) placed
close to pins 5 and 6. If the VCCline 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 fre­quency of the power supplies (about 250kHz). If alu­minum electrolytics are used, higher capacitance val­ues may be required.

MAX218

™ LapLink is a trademark of Traveling Software, Inc.

_______________________________________________________________________________________ 5

1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver

Table 1. Suggested Component Suppliers

MANUFACTURER PART NUMBER PHONE FAX

Inductors—Surface Mount

Murata-Erie LQH4N150K-TA

MAX218

Sumida CD43150

TDK NLC453232T-150K

Diodes—Surface Mount

Central Semiconductor CMPSH-3, Schottky USA [phone] USA [phone]
Motorola MMBD6050LT1, Silicon USA [phone] USA [phone]
Philips PMBD6050, Silicon USA [phone] USA [phone]

Diodes—Through-Hole

Motorola

1N6050, Silicon
1N5817, Schottky

USA [phone]
Japan [phone]

USA [phone]
Japan [phone]

USA [phone]
Japan [phone]

USA [phone] USA [phone]

USA [phone]
Japan [phone]

USA [phone]
Japan [phone]

USA [phone]
Japan [phone]

The two drivers are identical, and deliver EIA/TIA-232E

RS-232 Drivers

and EIA/TIA-562 output voltage levels when VDDis
between 1.8V and 4.25V. The transmitters drive up to
3kΩ in 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 opera­tion, as shown in Table 2.

Table 2. Operating Modes

–S—H—D—N–

L L High-Z High-Z OFF
L H Enabled High-Z OFF
H L High-Z Enabled ON
H H Enabled Enabled ON

EN

RECEIVER

OUTPUT

DRIVER

OUTPUT

DC-DC

CONVERTER

SUPPLY

CURRENT

Minimum
Minimum

Normal
Normal

When S—H—D—N–is low, the power supplies are disabled and

Shutdown

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 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 0.1µF 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 con­nected to it.

6 _______________________________________________________________________________________

1.8V to 4.25V-Powered,

True RS-232 Dual Transceiver

D1

1N6050

15µH

C1+

C1-

1µF

C2

15

V-

1µF

C3

18

0.47µF

16

C1

14

13

12

11

3V

1µF

DC-DC

CONVERTER

MAX878
MAX756
MAX856

Figure 2. Operating from Unregulated and Regulated Supplies

C5



OR



OR

ON/OFF

ENABLE

0.1µF

6

V

CC

C4

3

SHDN

T1IN

7

T2IN

8

9

R1OUT

R2OUT

10

19

1

V+

LX

MAX218

T1OUT

T1

T2OUT

T2

R1IN

R1

R2IN

R2

EN

GND

4

5, 17, 20

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

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 S—H—D—N–pin low while power is being applied to
the MAX218, and take S—H—D—N–high only after VCChas
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 pow­ered from rechargeable cells; if S—H—D—N–is h igh 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 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.

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 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
3kΩ 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.

MAX218

_______________________________________________________________________________________ 7

1.8V to 4.25V-Powered,
True RS-232 Dual Transceiver

______3V-Powered EIA/TIA-232 and EIA/TIA-562 Transceivers from Maxim

No. OF

RECEIVERS

ACTIVE IN

SHUTDOWN

PART

SUPPLY

VOLTAGE

(V)

No. OF

TRANSMITTERS/

RECEIVERS

MAX218

___________________Chip Topography

LX

SHDN

GND

EN

V+

C1+
GND

C1­V-

GUARANTEED

DATA RATE

(kbps)

0.101"

(2.565mm)

EIT/TIA-

232

OR 562

23212053/52.7 to 3.6MAX3212

23212022/21.8 to 4.25MAX218

23212022/23.0 to 5.5MAX3241

23212013/53.0 to 5.5MAX3243

FEATURES

Drives mice23212053/53.0 to 3.6MAX212
AutoShutdown, complementary receiver,

drives mice, transient detection
Operates directly from a battery

without a voltage regulator
Same as MAX218, but with AutoShutdown23212022/21.8 to 4.25MAX3218

Pin-compatible with MAX21356212024/53.0 to 3.6MAX560
Pin-compatible with MAX21456212004/53.0 to 3.6MAX561
Wide supply range56223053/52.7 to 5.25MAX562

0.1µF capacitors56212022/23.0 to 3.6MAX563

0.1µF capacitors23212022/23.0 to 5.5MAX3222

0.1µF capacitors23212022/23.0 to 5.5MAX3223
Pin-compatible with MAX23223212022/23.0 to 5.5MAX3232

0.1µF capacitors, 2 complementary
receivers, drives mice

0.1µF capacitors, AutoShutdown,
complementary receivers, drives mice

GND

T1IN

V

CC

T2IN

R1OUT

(3.099mm)

R2OUT

0.122"

R2IN

R1IN

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

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© 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.