19-0380; Rev 0; 3/95
1µA Supply Current, 1.8V to 4.25V-Powered
RS-232 Transceiver with AutoShutdown™
_______________General Description
The MAX3218 RS-232 transceiver is intended for bat -
tery-powered EIA/TIA-232E and V.28/V.24 communica-
tions interfaces that need two drivers and two receivers
with minimum power consumption from a single low-
voltage supply. It provides a wide +1.8V to +4.25V
operating voltage range while maintaining true RS-232
and EIA/TIA-562 voltage levels. The MAX3218 runs
from two alkaline, NiCd, or NiMH cells without any form
of voltage regulator. A guaranteed 120kbps data rate
provides compatibility with popular software for com -
municating with personal computers.
Supply current is reduced to 1 µA with Maxim’s new
AutoShutdown™ feature. When the MAX3218 does not
sense a valid signal level on the receiver inputs, the on-
board power-supply and drivers shut down. This
occurs if the RS-232 cable is disconnected or if the
transmitters of the connected peripheral are turned off.
The system turns on again when a valid level is applied
to either RS-232 receiver input. As a result, the system
saves power without changes to the existing software.
Additionally, the MAX3218 can be forced into or out of
shutdown, under logic control.
While shut down, all receivers can remain active or can
be disabled under logic control, permitting a system
incorporating the CMOS MAX3218 to monitor external
devices while in low-power shutdown. Three-state dri -
vers are provided on both receiver outputs so that multi -
ple receivers, generally of different interface standards,
can be on the same bus. The MAX3218 is available in
20-pin DIP and SSOP packages.
____________________________Features
BETTER THAN BIPOLAR!
o
1µA Supply Current Using AutoShutdown™
o
Operates Directly from Two Alkaline,
NiCd or NiMH Cells
o
+1.8V to +4.25V Single-Supply Voltage Range
o
120kbps Data Rate Guaranteed
o
Low-Cost Surface-Mount Components
o
Meets EIA/TIA-232E Specifications
o
Three-State Receiver Outputs
o
Flow-Through Pinout
o
On-Board DC-DC Converters
o
20-Pin SSOP and DIP Packages
MAX3218*
______________Ordering Information
PART
MAX3218CPP
MAX3218CAP
MAX3218C/D
MAX3218EPP
MAX3218EAP
TEMP. RANGE
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
PIN-PACKAGE
20 Plastic DIP
20 SSOP
Dice
†
20 Plastic DIP
20 SSOP
†
Contact factory for dice specifications.
________________________Applications
Battery-Powered Equipment
Subnotebook Computers
PDAs
Hand-Held Equipment
Peripherals
Cellular Phones
__________________Pin Configuration
TOP VIEW
LX 1
INVALID 2
FORCEON 3
FORCEOFF 4
GND 5
V
CC
6
T1IN 7
T2IN 8
R1OUT 9
R2OUT 10
20 GND
19 V+
18 C1+
17 GND
MAX3218
16 C1-
15 V-
14 T1OUT
13 T2OUT
12 R1IN
11 R2IN
*
™ AutoShutdown is a trademark of Maxim Integrated Products.
DIP/SSOP
1
________________________________________________________________
Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1µA Supply Current, 1.8V to 4.25V-Powered
RS-232 Transceiver with AutoShutdown™
MAX3218
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, FORCEON, FORCEOFF ............................ -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
SSOP (derate 8.00mW/°C above +70°C) ..................640mW
Operating Temperature Ranges
MAX3218C_ P ................................................... 0°C to +70°C
MAX3218E_ 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
Typical values are at V
CC
= 3.0V, T
A
= +25°C.)
PARAMETER
DC CHARACTERISTICS
Operating Voltage Range
Supply Current, AutoShutdown™
Supply Current, Shutdown
Supply Current,
AutoShutdown™ Disabled
Input Logic Threshold Low
Input Logic Threshold High
Input Leakage Current
Output Voltage Low
Output Voltage High
Output Leakage Current
V
CC
= 3.0V, T
A
= +25°C, all R_IN open,
FORCEON = GND, FORCEOFF = V
CC
FORCEOFF = GND, T
A
= +25°C, V
CC
= 3.0V
FORCEON = FORCEOFF = V
CC
= 3.0V, no load
1.8
1.0
1.0
2.0
4.25
10
10
3.0
V
µA
µA
mA
CONDITIONS
A
= T
MIN
to T
MAX
, unless otherwise noted.
TYP
MAX
UNITS
MIN
LOGIC INPUTS AND RECEIVER OUTPUTS
T_IN, FORCEON, FORCEOFF
T_IN, FORCEON, FORCEOFF
T_IN, FORCEON = FORCEOFF = 0V or V
CC
R_OUT, I
OUT
= 1.0mA
R_OUT, I
OUT
= -0.4mA
R_OUT, 0V
≤
R_OUT
≤
V
CC
,
FORCEON = FORCEOFF = 0V
Positive threshold
Negative threshold
V
CC
- 0.25
V
CC
- 0.08
0.05
±10
0.67 x V
CC
0.001
±1
0.4
0.33 x V
CC
V
V
µA
V
V
µA
AUTOSHUTDOWN (FORCEON = GND, FORCEOFF = V
CC
)
Receiver Input Thresholds,
Transmitters Enabled
Receiver Input Thresholds
Transmitters Disabled
INVALID Output Low Voltage
INVALID Output High Voltage
Figure 4a
2.8
-2.8
-0.3
0.3
0.4
V
CC
- 0.25
V
V
V
V
1µA supply current, Figure 4a
I
OUT
= 1.0mA, -0.3V < R_IN < 0.3V
I
OUT
= -0.4mA,
|
R_IN
|
> 2.8V
2
_______________________________________________________________________________________
1µA Supply Current, 1.8V to 4.25V-Powered
RS-232 Transceiver with AutoShutdown™
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
CC
= 1.8V to 4.25V, C1 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, T
Typical values are at V
CC
= 3.0V, T
A
= +25°C.)
PARAMETER
EIA/TIA-232E RECEIVER INPUTS
Input Voltage Range
Input Threshold Low
Input Threshold High
Input Hysteresis
Input Resistance
Output Voltage Swing
Output Resistance
Output Short-Circuit Current
-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
-25
0.4
0.3
3.0
2.8
+25
V
V
V
V
kΩ
CONDITIONS
A
MAX3218
= T
MIN
to T
MAX
, unless otherwise noted.
TYP
MAX
UNITS
MIN
TIMING CHARACTERISTICS
(Circuit of Figure 1, V
CC
= 1.8V to 4.25V, C1 = 0.47µF, C2 = C3 = C4 = 1µF, L1 = 15µH, T
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
2500pF
||
3kΩ load each transmitter, one trans-
mitter switching, 150pF load each receiver
A
= T
MIN
to T
MAX
, unless otherwise noted.
MIN
120
TYP
235
90
200
250
500
290
260
1.9
1.8
MAX
UNITS
kbps
300
500
450
1000
1000
2.7
2.7
30
ns
ns
µs
ns
ns
µs
Transition Region Slew Rate
AUTOSHUTDOWN TIMING
Receiver Threshold to
Transmitters Enabled
Receiver Positive or Negative
Threshold to INVALID High
Receiver Positive or Negative
Threshold to INVALID Low
t
WU
t
INVH
t
INVL
V/µs
Figure 4b
Figure 4b
Figure 4b
250
1
30
µs
µs
µs
_______________________________________________________________________________________
3
1µA Supply Current, 1.8V to 4.25V-Powered
RS-232 Transceiver with AutoShutdown™
MAX3218
__________________________________________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
MAX3218-01
TRANSMITTING SUPPLY CURRENT
vs. LOAD CAPACITANCE
V
CC
= 2.4V
90
SUPPLY CURRENT (mA)
80
70
60
50
40
30
20
20kbps
1000
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
240kbps
80
60
40
20
0
1.8
2.4
3.0
3.6
4.2
SUPPLY VOLTAGE (V)
120kbps
20kbps
0kbps
1 TRANSMITTER FULL DATA RATE
1 TRANSMITTER 1/8 DATA RATE
R
L
= 3kΩ + 2500pF
100
0
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
TIME TO EXIT SHUTDOWN
(ONE TRANSMITTER HIGH,
ONE TRANSMITTER LOW)
FORCEON, FORCEOFF
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
MAX3218-04
SLEW RATE vs.
TRANSMITTER CAPACITANCE
MAX3218-05
8
TRANSMITTER OUTPUT VOLTAGE (V)
6
4
2
0
-2
-4
V
OUT-
-6
-8
0
1000
2000
3000
4000
V
OUT+
12
10
SLEW RATE (V/µs)
+SLEW
8
6
4
2
0
DATA RATE 120kbps,
TRANSMITTERS LOADED WITH
3kΩ PLUS INDICATED CAPACITANCE
0
1000
2000
3000
4000
-SLEW
5000
5000
LOAD CAPACITANCE (pF)
LOAD CAPACITANCE (pF)
4
_______________________________________________________________________________________
1µA Supply Current, 1.8V to 4.25V-Powered
RS-232 Transceiver with AutoShutdown™
______________________________________________________________Pin Description
PIN
NAME
LX
INVALID
FORCEON
FORCEOFF
GND
V
CC
T1IN, T2IN
R1OUT, R2OUT
R2IN, R1IN
T2OUT, T1OUT
V-
C1-, C1+
V+
Inductor/Diode Connection Point
Output of Invalid Signal Detector. Low if invalid RS-232 levels are present on all receiver inputs,
otherwise high.
Drive high when FORCEOFF = high to override automatic circuitry, keeping transmitters on.
Drive low to shut down transmitters and on-board power supply, overriding all automatic
circuitry and FORCEON.
Ground
Supply Voltage Input, 1.8V to 4.25V. Bypass to GND with at least 1µF.
Transmitter Inputs
Receiver Outputs
Receiver Inputs
Transmitter Outputs, swing between V+ and V-
Negative Supply generated on-board
Terminal for Charge-Pump Capacitor
Positive Supply generated on-board
FUNCTION
MAX3218
1
2
3
4
5, 17, 20
6
7, 8
9, 10
11, 12
13, 14
15
16, 18
19
_______________Detailed Description
The MAX3218 line driver/receiver is intended for bat-
tery-powered EIA/TIA-232 and V.28/V.24 communica -
tions 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 regu-
lator. For example, the MAX3218 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 MAX3218.
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.
The MAX3218 is equipped with Maxim’s new propri -
etary AutoShutdown™ circuitry. This achieves a 1µA
supply current by shutting down the device when the
RS-232 cable is disconnected or when the connected
peripheral transmitters are turned off. While shut down,
both receivers can remain active or can be disabled
under logic control. With this feature, the MAX3218 can
be in low-power shutdown mode and still monitor activi-
ty on external devices. Three-state drivers are provid-
ed on both receiver outputs.
Three-state drivers on both receiver outputs are provid-
ed so that multiple receivers, generally of different inter-
face standards, can be wire-ORed at the UART.
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.
Switch-Mode Power Supply
Inductor Selection
Use a 15µH inductor with a saturation current rating of at
least 350mA and less than 1
Ω
resistance. Table 1 lists
suppliers of inductors that meet the 15 µH/350mA/1Ω
specifications.
™ LapLink is a trademark of Traveling Software, Inc.
AutoShutdown is a trademark of Maxim Integrated Products.
_______________________________________________________________________________________
5
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