________________General Description
The MAX212 RS-232 transceiver is intended for 3V-pow-
ered EIA/TIA-232E and V.28/V.24 communication inter-
faces where 3 drivers and 5 receivers are needed with
minimum power consumption. The operating voltage
range extends from 3.6V down to 3.0V while still main-
taining true RS-232 and EIA/TIA-562 voltage levels.
A 1µA typical shutdown mode reduces power con-
sumption, extending battery life in portable systems.
While shut down, all receivers can remain active or can
be disabled under logic control. This enables a system
incorporating the CMOS MAX212 to be in low-power
shutdown mode and monitor incoming RS-232 activity.
A guaranteed data rate of 120kbps provides compati-
bility with popular software for communicating with per-
sonal computers.
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 MAX212 is available in both small-outline (SO) and
shrink-small-outline (SSOP) packages. The SSOP
package occupies less than half of the board area
required by the equivalent SO package.
________________________Applications
Computers
Notebooks/Palmtops/Subnotebooks
Printers
Peripherals
Instruments
____________________________Features
SUPERIOR TO BIPOLAR:
♦Operates from Single +3.0V to +3.6V Supply
♦24-Pin SSOP or Wide SO Packages
♦Meets All EIA/TIA-232E & EIA/TIA-562
Specifications
♦3mA Max Supply Current (Unloaded)
♦1µA Low-Power Shutdown Mode
♦All Receivers Active During Low-Power Shutdown
♦Mouse Compatible at 3.0V
♦Low-Cost, Surface-Mount External Components
♦120kbps Guaranteed Data Rate—LapLink™
Compatible
♦Three-State Receiver Outputs
♦Evaluation Kit Available
♦Flow-Through Pinout
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
PART TEMP. RANGE PIN-PACKAGE
MAX212CWG 0°C to +70°C 24 Wide SO
MAX212CAG 0°C to +70°C 24 SSOP
MAX212C/D 0°C to +70°C Dice*
MAX212EAG -40°C to +85°C 24 SSOP
MAX212EWG -40°C to +85°C 24 Wide SO
EV KIT TEMP. RANGE BOARD TYPE
MAX212EVKIT-SSOP 0°C to +70°C Surface Mount
19-0162; Rev 2; 2/94
™LapLink is a registered trademark of Traveling Software.
_______________Ordering Information
* Dice are tested at T
A
= +25°C only.
___________Typical Operating Circuit
MAX212
T1IN
VCC
SD
+3.3V
DC-DC CONVERTER
EN
T1OUT
LN LP V-V+
GND
121423
T1
SHUTDOWN
11
3
4
17
T2IN T2OUT
T2
12 16
T3IN T3OUT
T3
13 15
R1OUT R1IN
622
R2OUT R2IN
R2
721
R3OUT R3IN
820
R3
R4OUT R4IN
919
R4
R5OUT R5IN
10 18
R5
524
ENABLE
R1
EVALUATION KIT
INFORMATION INCLUDED
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = 3.0V to 3.6V, TA= TMIN to TMAX, unless otherwise noted.)
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.
PARAMETER MIN TYP MAX UNITS
Input Logic Threshold Low VCC / 3 V
115µA
Shutdown Supply Current 115µA
Input Logic Threshold High 2VCC / 3 V
Input Current High 1 µA
Input Current Low 1 µA
Hysteresis 0.3 V
Operating Voltage Range 3.0 3.6 V
VCC Supply Current 1.5 3.0 mA
Logic Output Voltage Low 0.25 V
Logic Output Voltage High VCC - 0.5 V
Logic Output Leakage Current ±10 µA
-25 +25 V
EIA/TIA-232E Input Hysteresis 0.7 V
EIA/TIA-232E Input Resistance 357kΩ
±5.0 ±5.5 V
Output Resistance 300 Ω
28 100 mA
CONDITIONS
IOUT = 1.0mA
T_IN, EN, –
S
—
D; VCC = 3.0V to 3.6V
IOUT = -1.0mA
–
S
—
D = GND, EN = VCC, R_IN = GND or VCC
–
S
—
D= EN = GND, R_IN = GND or VCC
T_IN, EN, –
S
—
D; VCC = 3.0V to 3.6V
T_IN, EN, –
S
—
D; VIN = VCC
EN = GND, 0V < R_OUT < VCC
T_IN, EN, –
S
—
D, VIN = GND
T_IN; VCC = 3.3V
-15V < VIN < 15V
Meets or exceeds EIA/TIA-232E specifications
All transmitters loaded 3kΩto GND
VCC = V- = V+ = 0V, -2V < T_OUT < 2V
No load, VCC = 3.3V
Supply Voltages
VCC.....................................................................-0.3V to +4.6V
V+............................................................(VCC - 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, –
S
—
D, EN ..............................................-0.3V to (V+ + 0.3V)
R_IN...................................................................................±25V
Output Voltages
T_OUT................................................................................±15V
R_OUT........................................................-0.3V to (V+ + 0.3V)
Short-Circuit Duration, T_OUT.....................................Continuous
Continuous Power Dissipation (TA= +70°C)
Wide SO (derate 11.76mW/°C above +70°C)...............941mW
SSOP (derate 8.00mW/°C above +70°C) .....................640mW
Lead Temperature (soldering, 10sec).............................+300°C
Shutdown Supply Current with
Receivers Active
EIA/TIA-232E Input Voltage
Operating Range
EIA/TIA-232E Input Voltage
Threshold Low 0.4 V
EIA/TIA-232E Input Voltage
Threshold High 2.8 V
Output Voltage Swing (VHIGH, VLOW)
EIA/TIA-232E Short-Circuit Current
DC CHARACTERISTICS
LOGIC
EIA/TIA-232E RECEIVERS
EIA/TIA-232E TRANSMITTERS
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
_______________________________________________________________________________________ 3
TIMING CHARACTERISTICS
(VCC = 3.0V to 3.6V, TA= TMIN to TMAX, unless otherwise noted.)
PARAMETER MIN TYP MAX UNITS
Transmitter Output Disable Time 600 ns
250 µs
Receiver Output Enable Time 70 200 ns
Receiver Output Disable Time 420 700 ns
CONDITIONS
Includes power-supply start-up
Receiver Propagation Delay 300 700 ns150pF load
800 2000
Transmitter Propagation Delay 800 2000 ns
2500pF 3kΩload
300 700
SYMBOL
tPLHR
tPHLT
tPLHT
tDT
tPHLR
tET
tER
tDR
Transmitter Output Enable Time
4.0 10 30 V/µs
RL= 3kΩto 7kΩ, CL= 50pF to 2500pF,
measured from +3V to -3V or -3V to +3V
Transition-Region Slew Rate
__________________________________________Typical Operating Characteristics
(VCC = 3.3V, TA = +25°C, unless otherwise noted.)
0204060
DATA RATE (kbps)
SUPPLY POWER (mW)
60
80
120
140
180
160
SUPPLY POWER vs.
DATA RATE
100
212 GR4
2500pF
1000pF
2500pF
80
ALL TRANSMITTERS
LOADED w/ 3kΩ AND
STATED CAPACITANCE
120
100
1000pF
3 TRANSMITTERS
AT DATA RATE
3 TRANSMITTERS,
1 AT DATA RATE,
1 LOW, 1 HIGH
0 50 100 150
DATA RATE (kbps)
OUTPUT VOLTAGE (V)
-6
-4
0
2
6
4
TRANSMITTER OUTPUT VOLTAGE vs.
DATA RATE
212 GR5
5000pF
4000pF
2500pF
1000pF
200 250
-2
4000pF
2500pF
1000pF
5000pF
ALL TRANSMITTERS
LOADED SIMULTANEOUSLY
w/ SPECIFIED CAPACITANCE AND 3kΩ
Data Rate 120 250 kbps
1000pF 3kΩload on each transmitter,
150pF load on each receiver
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
4 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(VCC = 3.3V, TA = +25°C, unless otherwise noted.)
500 1500 2500 3500
LOAD CAPACITANCE (pF)
SLEW RATE (V/µs)
6
7
9
10
12
11
SLEW RATE vs.
LOAD CAPACITANCE
212 GR6
4500
8
RISING EDGE
ALL TRANSMITTERS
LOADED SIMULTANEOUSLY
w/ SPECIFIED CAPACITANCE AND 3kΩ
13
14
FALLING EDGE
NAME FUNCTION
LN
LP
VCC Supply Voltage Input, 3.0V to 3.6V
1
2
–
S
—
D
EN
R1OUT-
R5OUT Receiver Outputs, swing GND
to VCC
T1IN-T3IN Transmitter Inputs
3
4
5
Transmitter Outputs
R5IN-R1IN Receiver Inputs
6-10
11-13
15-17
18-22
_____________________Pin Description
PIN
T3OUT-
T1OUT
V+ Positive Supply generated on-board23
GND Ground24
V-14
Inductor/Diode Connection Point
Inductor/Diode Connection Point
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 Enable Control. Connect
to VCC for normal operation.
Connect to GND to force the
receiver outputs into a high-Z state.
Negative Supply generated on-board
_______________Detailed Description
The MAX212 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 3.0V 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 sec-
tion converts the supplied 3V to about ±6.5V, to pro-
vide 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 data rates of 120kbps.
A shutdown mode reduces current to 1µA to extend
battery life in portable systems. While shut down, all
receivers can remain active or can be disabled under
logic control. This enables a system incorporating the
MAX212 to be in low-power shutdown mode and still
monitor incoming 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.
2.5 3.0 3.5 4.0
SUPPLY VOLTAGE (V)
SUPPLY POWER (mW)
80
100
120
140
180
160
SUPPLY POWER vs.
SUPPLY VOLTAGE
4.5
212 GR2
120kbps
ALL TRANSMITTERS
AT SPECIFIED DATA RATES
w/ 2500pF AND 3kΩ LOADS
64kbps
20kbps
0 1000 2000 3000
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
20
30
40
50
70
60
SUPPLY CURRENT vs.
LOAD CAPACITANCE
5000
212 GR3
120kbps
64kbps
20kbps
4000
80 ALL TRANSMITTERS
AT SPECIFIED CAPACITANCE AND
DATA RATES w/ 3kΩ LOADS
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
_______________________________________________________________________________________ 5
Switch-Mode Power Supply
The switch-mode power supply uses a single inductor
with two inexpensive diodes and two capacitors to
generate ±6.5V from the 3.0V to 3.6V input. Figure 1
shows the complete circuit for the power supply.
Use a 15µH inductor with a saturation current rating of at
least 350mA and under 1Ωresistance. Sample surface-
mount inductors are available from Maxim. Use 1N6050
diodes or equivalent. Surface-mount equivalents for the
1N6050 include the Motorola MMBD6050LT1, Philips
PMBD6050, and Allegro (formerly Sprague) TMPD6050LT.
For C1 and C2, use ceramic capacitors with values no
less than indicated in Figure 1. These capacitors deter-
mine the ripple on V+ and V-, but not the absolute volt-
ages. Bypass VCC to GND with at least 0.33µF close to
the MAX212. Increase this to 4.7µF if there are no other
VCC supply bypass components less than 6 inches
(15cm) away from the MAX212.
Component suppliers are listed in Table 1.
RS-232 Drivers
All three drivers are identical and deliver EIA/TIA-232E
and EIA/TIA-562 output voltage levels when VCC is
between 3.0V and 3.6V. Disable the drivers by taking
the –
S
—
Dpin to GND. The transmitter outputs are forced
into a high-impedance state when –
S
—
D is grounded.
RS-232 Receivers
All five receivers are identical and accept
EIA/TIA-232E and EIA/TIA-562 input signals. The CMOS
receiver outputs swing rail-to-rail (0V to VCC). When EN
is high, the receivers are active regardless of –
S
—
D’s status.
When EN is low, the receivers’ outputs are put into a
high-impedance state. This allows two RS-232 ports (or
two parts of different types) to be wire-ORed at the UART.
MAX212
T1IN
VCC
SD
+3.3V +3.3V TO ±6.5V
DC-DC CONVERTER
EN
T1OUT
LN LP V-V+
GND
L
15µH
D1
1N6050
121423
T1
C2
0.33µF
C1
0.68µF
C3
0.33µF
D2
1N6050
SHUTDOWN
11
3
4
17
T2IN T2OUT
T2
12 16
T3IN T3OUT
T3
13 15
R1OUT R1IN
622
R2OUT R2IN
R2
721
R3OUT R3IN
820
R3
R4OUT R4IN
919
R4
R5OUT R5IN
10 18
R5
524
ENABLE
R1
Figure 1. Typical Application Circuit
Table 1. Suggested Component Suppliers
MANUFACTURER PART NUMBER PHONE NUMBER FAX NUMBER
Allegro TMPD6050LT USA (508) 853-5049
Motorola MMBD6050LT1 USA (408) 991-7420
Murata LQH4N150K-TA
Philips PMBD6050 USA (401) 762-3800 USA (401) 767-4493
Sumida CD43150 USA (708) 956-0666
Japan (03) 3607-5111
TDK NLC453232T-150K USA (708) 803-6296
Japan (03) 3278-5358
USA (508) 853-5000
USA (408) 749-0510
USA (404) 831-9172
Japan (075) 951-9111 USA (404) 436-3030
Japan (075) 955-6526
USA (708) 956-0702
Japan (03) 3607-5428
USA (708) 803-6100
Japan (03) 3278-5111
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
6 _______________________________________________________________________________________
Operating Modes
–
S
—
D and EN determine the operation of the MAX212
as follows:
Shutdown
V+ and V- are disabled and the transmitters are put into
a high-impedance state when –
S
—
Dis taken to logic low.
Receiver operation is not affected, but power consump-
tion is dramatically reduced while in shutdown mode.
Supply current is minimized when the receiver inputs are
static in any of three states: floating (ground), less than
GND, or greater than VCC. This will be true for all static
RS-232 conditions. The presence of AC signals on receiv-
er inputs will increase VCC current in shutdown.
From a low-power system perspective, powering-up with
non-critical or unused sections of circuitry shut down or
deselected is generally recommended. Activating these
sections only when required saves power and reduces
power-up current surges. Powering-up the MAX212 in
shutdown mode (holding the shutdown pin,
–
S
—
D, low until VCC > 2.7V), helps to achieve this.
Driving the MAX212 from 5V Logic
The MAX212 can interface with 5V logic while it operates
from a 3V supply, however a 200kΩseries resistor between
–
S
—
D and the +5V logic signal is required (see Figure 2).
This protects the MAX212 by preventing –
S
—
Dfrom sinking
current while V+ is powering up. Also, the UART must not
be permitted to send a logic high to the MAX212’s EN or
transmitter input pins until –
S
—
Dis high (not shut down).
Mouse Driveability
The MAX212 has been specifically designed to power
serial mice while operating from low-voltage power
supplies. It has been tested with samples of ten major
mouse models from six manufacturers, including the
leading three, Logitech (5 models), Mouse Systems,
and Microsoft. The MAX212 successfully drove all seri-
al mice and met their respective current and voltage
requirements (Figure 1).
Figure 3 shows the transmitter output voltages under
increasing load current. The MAX212’s switching regu-
lator ensures the transmitters will supply at least ±5V
during worst-case load conditions.
EIA/TIA-232E and 562 Standards
Most of the power drawn by RS-232 circuits is con-
sumed because the EIA/TIA-232E standard demands
that at least ±5V be delivered by the transmitters to
impedances that can be as low as 3kΩ. For applica-
–
S
—
DEN RECEIVER
OUTPUTS DRIVER
OUTPUTS
L L High-Z High-Z Off Minimum
L H Enabled High-Z Off Minimum
H L High-Z Enabled On Normal
H H Enabled Enabled On Normal
SUPPLY
CURRENT
PART No. OF
TRANSMITTERS/
RECEIVERS
DATA RATE
(kbps) FEATURES
MAX212 3.0 to 3.6 3/5 5 250 True RS-232 from +3V
MAX560 3.0 to 3.6 4/5 2 120 2 receivers active in shutdown
MAX561 3.0 to 3.6 4/5 0 120 Pin compatible with MAX241
MAX562 2.7 to 5.25 3/5 5 250 Wide supply range
POWER-SUPPLY
VOLTAGE
(V)
No. OF
RECEIVERS
ACTIVE IN
SHUTDOWN
____________________________+3V Powered RS-232 Transceivers from Maxim
DC-DC
CONVERTER
MAX212
T_IN
SD
+3.3V DC-DC CONVERTER
R_OUT R_IN
TX
X3
RX
X5
EN
T_OUT
LN LP V-
GND
+5V
LOGIC
SIGNALS
200k
V+
Figure 2. Connecting to +5V Logic
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
_______________________________________________________________________________________ 7
tions where power consumption is especially critical,
the EIA/TIA-562 standard provides an alternative.
EIA/TIA-562 transmitter output voltage levels need only
reach ±3.7V, and because they need only drive the
same 3kΩreceiver loads specified by RS-232, total
power consumption is considerably reduced. Since the
EIA/TIA-232E and EIA/TIA-562 receiver input voltage
thresholds are the same, interoperability between the two
standards is guaranteed and devices from both stan-
dards will communicate with each other successfully.
Maxim’s MAX560 and MAX561 are EIA/TIA-562 trans-
ceivers 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.
______________________Evaluation Kit
The MAX212 evaluation kit (EV kit) is a fully assem-
bled and tested, surface-mount demonstration board
that provides quick and easy evaluation of the
MAX212.
The MAX212 EV kit is intended for 3.3V ±300mV-pow-
ered EIA/TIA-232E and V.28/V.24 communications
interfaces where 3 drivers and 5 receivers are needed
with minimum power consumption.
A logic or pin-selectable shutdown mode reduces
current to 1µA. While shut down, all receivers can
remain active or can be disabled under logic control
via the EN input.
Figure 4. MAX212 Evaluation Kit
12 34
LOAD CURRENT PER TRANSMITTER (mA)
TRANSMITTER OUTPUT VOLTAGE (V)
-6
-4
-2
0
2
6
4
TRANSMITTER OUTPUT VOLTAGE vs.
LOAD CURRENT PER TRANSMITTER
5 6
212 GR1
T1OUT AND T2OUT
T3OUT
T1IN AND T2IN = GND,
T3IN = VCC = 3.0V,
T3OUT, T2OUT, T1OUT
ALL LOADED
SIMULTANEOUSLY
Figure 3. Mouse Emulation Circuit Current
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
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1993 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX212
+3V-Powered, Low-Power,
True RS-232 Transceiver
___________________Chip Topography
SD
VCC
R1OUT
VCC LP GND V+
T1IN
0.15"
(3.81mm)
0.1"
(2.54mm)
V-
GNDLN
EN
R2OUT
R3OUT
R4OUT
R5OUT
T2IN
T3IN
T3OUT
T2OUT
T1OUT
R1IN
R2IN
R3IN
R4IN
R5IN
TRANSISTOR COUNT: 1382 ;
SUBSTRATE CONNECTED TO V+.
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
GND
V+
R1IN
R2IN
SD
VCC
LP
LN
TOP VIEW
R3IN
R4IN
R5IN
T1OUT
R3OUT
R2OUT
R1OUT
EN
16
15
14
13
9
10
11
12
T2OUT
T3OUT
V-
T3IN
T2IN
T1IN
R5OUT
R4OUT
SSOP/WIDE SO
MAX212
_________________Pin Configuration
