19-0312; Rev 0; 9/94
+2.7V to +3.6V-Powered, 1µA Supply Current,
3-Driver/5-Receiver, True RS-232 Transceiver
_______________General Description
The MAX3212 uses Maxim’s new proprietary Auto-
Shutdown mode to reduce supply current to 1µA. The
MAX3212, with 3 RS-232 drivers and 5 RS-232 receivers,
is intended for 2.7V to 3.6V-powered EIA/TIA-232E and
V.28/V.24 serial interface. True RS-232 levels are main-
tained across the operating range. A guaranteed data
rate of 235kbps provides compatibility with popular soft-
ware for communicating with personal computers.
Supply current is reduced to 1 µA with Maxim’s new
AutoShutdown feature. When the MAX3212 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 transmit-
ters of the connected peripheral are turned off. The sys-
tem turns on again when a valid level is applied to any
RS-232 receiver input. As a result, the system saves
power without changes to the existing software.
A second power-management feature is incorporated to
permit automatic shutdown when the RS-232 connection
is valid but inactive. In this case, a transition detector
facilitates shutdown when the receivers are presented
with stationary RS-232 levels for long periods.
Three-state drivers are provided on receiver outputs so
that multiple receivers, generally of different interface
standards, can be wire-ORed at the UART. The
MAX3212 is available in 28-pin SO and SSOP packages.
____________________________Features
BETTER THAN BIPOLAR!
1µA Supply Current Using AutoShutdown
Operates from Single +2.7V to +3.6V Supply
28-Pin SSOP or Wide SO Packages
Meets All EIA/TIA-232E & EIA/TIA-562 Specifications
Mouse Driveability–Guaranteed
Low-Cost, Surface-Mount External Components
235kbps Guaranteed Data Rate–
LapLink™ Compatible
o
+5V Logic Compatible
o
Complementary Receiver Output Always Active
o
Flow-Through Pinout
o
o
o
o
o
o
o
MAX3212*
__________Typical Operating Circuit
0.68µF 1N6050 15µH
+3.0V
0.33µF
3 27
1
V
CC
V+ LN
26 FORCEON
+3.0V
25 FORCEOFF
5 TRAN
6
INVALID
T1
T2
T3
R1
5k
9 R2OUT
R2
5k
10 R3OUT
R3
5k
11 R4OUT
R3IN 22
R2IN 23
T1OUT 19
T2OUT 18
T3OUT 17
R1IN 24
13 T1IN
14 T2IN
15 T3IN
1N6050
2 16
LP
V-
0.33µF
MAX3212
________________________Applications
Notebook and Palmtop Computers
Peripherals
Instruments
Battery-Powered Equipment
8 R1OUT
______________Ordering Information
PART
MAX3212CWI
MAX3212CAI
MAX3212EWI
MAX3212EAI
TEMP. RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 Wide SO
28 SSOP
28 Wide SO
28 SSOP
+3.0V
EN
4
12 R5OUT
7 R5OUTB
R4
5k
R5
R5
5k
GND
28
R4IN 21
R5IN 20
AUTOSHUTDOWN OPERATION
FORCEOFF = HIGH, FORCEON = LOW
Pin Configuration appears at end of data sheet.
* ng
RS-232 Present
Yes
No
Status
On
Shut Down
________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
+2.7V to +3.6V-Powered, 1µA Supply Current,
3-Driver/5-Receiver, True RS-232 Transceiver
MAX3212
ABSOLUTE MAXIMUM RATINGS
Supply Voltages
V
CC
.....................................................................-0.3V to +4.6V
V+ ............................................................(V
CC
- 0.3V) to +7.4V
V- ........................................................................-7.4V to +2.0V
LN ..............................................................-0.3V to (V+ + 1.0V)
LP.......................................................(V- - 1.0V) to (V+ + 0.3V)
Input Voltages
T_IN, EN, FORCEON, FORCEOFF .....................-0.3V to +7.0V
R_IN ..................................................................................±25V
Output Voltages
T_OUT...............................................................................±15V
R_OUT, R5OUTB, INVALID, TRAN............-0.3V to (V+ + 0.3V)
Short-Circuit Duration, T_OUT....................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
Wide SO (derate 11.76mW/°C above +70°C)...............941mW
SSOP (derate 8.00mW/°C above +70°C) .....................640mW
Operating Temperature Ranges
MAX3212C_ I .......................................................0°C to +70°C
MAX3212E_ I ....................................................-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
PARAMETER
DC CHARACTERISTICS
Operating Voltage Range
V
CC
Supply Current
(V
CC
= 2.7V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
CONDITIONS
Meets or exceeds EIA/TIA-232E specifications
All R_IN unconnected, FORCEON = GND
FORCEOFF = GND
FORCEON = FORCEOFF = V
CC
, no load
LOGIC INPUT AND RECEIVER OUTPUTS
Input Logic Threshold Low
Input Logic Threshold High
Input Current High
Input Current Low
Hysteresis
Logic Output Voltage Low
Logic Output Voltage High
Logic Output Leakage Current
Receiver Input Thresholds,
Transmitters Enabled
Receiver Input Thresholds,
Transmitters Disabled
INVALID Output Voltage Low
INVALID Output Voltage High
Receiver Threshold to Transmitters
Enabled, t
WU
Receiver Positive or Negative
Threshold to Invalid High, t
INVH
Receiver Positive or Negative
Threshold to Invalid Low, t
INVL
2
T_IN, EN, FORCEON, FORCEOFF
T_IN, EN, FORCEON, FORCEOFF
T_IN, EN, FORCEON, FORCEOFF
T_IN, EN, FORCEON, FORCEOFF
T_IN, V
CC
= 3.3V
I
OUT
= 1.0mA
I
OUT
= -1.0mA
EN = GND, 0V < R_OUT < V
CC
Positive threshold
Negative threshold
-3.0
-0.3
0.3
0.4
V
CC
- 0.6
250
1
30
V
CC
- 0.5
±10
3.0
0.3
0.4
0.67V
CC
+ 0.1
1
1
0.3V
CC
- 0.1
V
V
µA
µA
V
V
V
µA
MIN
2.7
1
1
1.5
TYP
MAX
3.6
10
10
3.0
UNITS
V
µA
µA
mA
AUTOSHUTDOWN
(FORCEON = GND, FORCEOFF = V
CC
)
Figure 4
V
V
V
V
µs
µs
µs
1µA supply current, Figure 4
I
OUT
= 1.0mA
I
OUT
= -1.0mA
Figure 4b
Figure 4
Figure 4
_______________________________________________________________________________________
+2.7V to +3.6V-Powered, 1µA Supply Current,
3-Driver/5-Receiver, True RS-232 Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 2.7V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
EIA/TIA-232E RECEIVERS
Input Voltage Operating Range
Input Voltage Threshold Low
Input Voltage Threshold High
Input Hysteresis
Input Resistance
EIA/TIA-232E TRANSMITTERS
EIA/TIA-232E TRANSMITTERS
Output Voltage Swing (V
HIGH
, V
LOW
)
Output Resistance
EIA/TIA-232E Short-Circuit Current
MOUSE DRIVEABILITY
Transmitter Output Voltage
TIN = T2IN = GND, T3IN = V
CC
,
T3OUT loaded with 3kΩ to GND,
T1OUT and T2OUT loaded with 5mA
±5
V
All transmitters loaded with 3kΩ to GND
V
CC
= V- = V+ = 0V, -2V < T_OUT < 2V
±5.0
300
28
60
±5.5
V
Ω
mA
-15V < V
IN
< 15V
3
0.7
5
7
-25
0.4
3.0
+25
V
V
V
V
kΩ
CONDITIONS
MIN
TYP
MAX
UNITS
MAX3212
TIMING CHARACTERISTICS
PARAMETER
Data Rate
Receiver Output Enable Time
Receiver Output Disable Time
Transmitter Output Enable Time
Transmitter Output Disable Time
Receiver Propagation Delay
Receiver Skew
Transmitter Propagation Delay
Transmitter Skew
Transition-Region Slew Rate
EN High to TRAN
Reset Delay
EN High Pulse Width
(V
CC
= 2.7V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
SYMBOL
CONDITIONS
R
L
= 3kΩ, C
L
= 1000pF, one transmitter
switching, 150pF load on each receiver
t
ER
t
DR
t
ET
t
DT
t
PHLR
t
PLHR
t
PHLT
t
PLHT
150pF load
Includes power-supply start-up
MIN
235
TYP
250
70
420
250
600
630
630
40
800
800
52
C
L
= 50pF to 2500pF
C
L
= 50pF to 1000pF
4.0
6
10
13
5
1
30
30
V/µs
2000
2000
2000
2000
200
700
MAX
UNITS
kbps
ns
ns
µs
ns
ns
ns
ns
ns
t
PHL -
t
PLH
2500pF
3kΩ load
t
PHL -
t
PLH
R
L
= 3kΩ to 7kΩ,
measured from +3V
to -3V or -3V to +3V
µs
µs
_______________________________________________________________________________________
3
+2.7V to +3.6V-Powered, 1µA Supply Current,
3-Driver/5-Receiver, True RS-232 Transceiver
MAX3212
__________________________________________Typical Operating Characteristics
(V
CC
= 3.3V, T
A
= +25°C, unless otherwise noted.)
TRANSMITTING SUPPLY CURRENT
vs. DATA RATE
MAX3212-01
TRANSMITTING SUPPLY CURRENT
vs. LOAD CAPACITANCE
60
55
SUPPLY CURRENT (mA)
50
45
40
35
30
25
20
15
0
1000
2000
3000
4000
5000
LOAD CAPACITANCE/TRANSMITTER (pF)
0
20kbps
-10
2.0
120kbps
235kbps
MAX3212-02
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
50
SUPPLY CURRENT (mA)
40
30
20
10
3kΩ + 120kbps
3kΩ + 20kbps
3kΩ ONLY
3kΩ + 235kbps
MAX3212-03
45
40
SUPPLY CURRENT (mA)
35
30
25
20
15
0
TRANSMITTERS LOADED
WITH 3kΩ + 2500pF
1 TRANSMITTER (FULL DATA RATE)
2 TRANSMITTERS (DATA RATE/8)
50
100
150
200
65
60
250
2.5
3.0
3.5
4.0
DATA RATE (kbps)
SUPPLY VOLTAGE (V)
SLEW RATE
vs. LOAD CAPACITANCE
MAX3212-04
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE AT 235kbps
TRANSMITTER OUTPUT VOLTAGE (V)
V
OUT
+
5.0
2.5
0
-2.5
-5.0
-7.5
V
OUT
-
TRANSMITTERS LOADED WITH 3kΩ
AND SPECIFIED CAPACITANCE
MAX3212-05
14
12
+SLEW
SLEW RATE (V/µs)
10
8
6
4
2
0
0
1000
2000
3000
4000
TRANSMITTERS LOADED
WITH 3kΩ AND SPECIFIED
CAPACITANCE AT 232kbps
-SLEW
7.5
5000
0
1000
2000
3000
4000
5000
LOAD CAPACITANCE/TRANSMITTER (pF)
LOAD CAPACITANCE/TRANSMITTER (pF)
TIME TO EXIT SHUTDOWN: ONE
TRANSMITTER HIGH, ONE TRANSMITTER LOW
FORCEON,
FORCEOFF
0V
2V/div
V
OH
0V
T_OUT
V
OL
R
L
= 3kΩ
||
2500pF
100µs/div
4
_______________________________________________________________________________________
+2.7V to +3.6V-Powered, 1µA Supply Current,
3-Driver/5-Receiver, True RS-232 Transceiver
______________________________________________________________Pin Description
PIN
1
2
3
4
NAME
LN
LP
V
CC
EN
Inductor/Diode Connection Point
Inductor/Diode Connection Point
Supply Voltage Input, 2.7V to 3.6V
Receiver Enable Control. Drive EN low to force receiver outputs into a high-Z state. Drive
EN high for normal operation. Cycle EN high then low to reset TRAN. TRAN is always low
when EN is high.
Transition Detection Output. TRAN latches high when a transition occurs on any receiver
input while EN is low. Reset by cycling the EN pin high then low.
Output of Invalid Signal Detector. Low if invalid RS-232 levels are present on all
receiver inputs, otherwise high.
Complementary Output of R5OUT—always active
Receiver Outputs. Swing from GND to V
CC
. High-impedance when EN is low.
Transmitter Inputs
Negative Supply generated on-board
Transmitter Outputs
Receiver Inputs
Drive low to shut down transmitters and on-board power supply, overriding all automatic
circuitry and FORCEON (see Figure 3).
Drive high to overide automatic circuitry, keeping transmitters on (see Figure 3).
FORCEOFF = high.
Positive Supply generated on-board
Ground
FUNCTION
MAX3212
5
6
7
8–12
13, 14, 15
16
17, 18, 19
20–24
25
26
27
28
TRAN
INVALID
R5OUTB
R1OUT–R5OUT
T1IN, T2IN, T3IN
V-
T3OUT, T2OUT, T1OUT
R5IN–R1IN
FORCEOFF
FORCEON
V+
GND
_______________Detailed Description
The MAX3212 line driver/receiver is intended for 3V-
powered EIA/TIA-232E and V.28/V.24 communications
interfaces where 3 drivers and 5 receivers are required.
The operating voltage range extends from 3.6V down to
2.7V while still maintaining true RS-232 and EIA/TIA-562
transmitter output voltage levels.
The circuit comprises three sections: power supply,
transmitters, and receivers. The power-supply section
converts the supplied 3V to about ±6.5V, to provide
the voltages necessary for the drivers to meet true RS-
232 levels. External components are small and inex -
pensive.
The transmitters and receivers are guaranteed to oper-
ate at data rates of 235kbps.
The MAX3212 is equipped with Maxim’s new propri -
etary AutoShutdown circuitry. This achieves a supply
current of 1 µA by shutting down the device when the
RS-232 cable is disconnected or when the connected
peripheral transmitters are turned off. While shut down,
all receivers can remain active or can be disabled
under logic control. A complementary receiver remains
active in all cases, enabling a system incorporating the
MAX3212 to remain shut down and still monitor incom-
ing RS-232 activity.
Three-state drivers on all receiver outputs are provided
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 two inexpensive diodes and two capacitors to
generate ±6.5V from the 2.7V to 3.6V input. The
Typical
Operating Circuit
shows the complete circuit for the pow-
er supply.
Use a 15µH inductor with a saturation current rating of at
least 350mA and under 1
Ω
resistance. Use 1N6050
diodes or equivalent. Surface-mount equivalents for the
1N6050 include the Motorola MMBD6050LT1, P hilips
PMBD6050, and Allegro (formerly Sprague) TMPD6050LT.
For C1 and C2, use ceramic capacitors with values no
less than indicated in the
Typical Operating Circuit
.
These capacitors determine the ripple on V+ and V-, but
5
Switch-Mode Power Supply
_______________________________________________________________________________________
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