Datasheet

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 1Ω resistance. 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 V
CC
to GND with at least 0.33µF close to
the MAX212. Increase this to 4.7µF if there are no other
V
CC
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 V
CC
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 V
CC
). 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
T1
IN
V
CC
SD
+3.3V
+3.3V TO ±6.5V
DC-DC CONVERTER
EN
T1
OUT
LN
LP V-V+
GND
L
15µH
D1
1N6050
1
21423
T1
C2
0.33µF
C1
0.68µF
C3
0.33µF
D2
1N6050
SHUTDOWN
11
3
4
17
T2
IN
T2
OUT
T2
12 16
T3
IN
T3
OUT
T3
13 15
R1
OUT
R1
IN
622
R2
OUT
R2
IN
R2
721
R3
OUT
R3
IN
820
R3
R4
OUT
R4
IN
919
R4
R5
OUT
R5
IN
10 18
R5
5
24
ENABLE
R1
Figure 1. Typical Application Circuit
Table 1. Suggested Component Suppliers
MANUFACTURER PART NUMBER PHONE NUMBER FAX NUMBER
Allegro TMPD6050LT USA [phone]
Motorola MMBD6050LT1 USA [phone]
Murata LQH4N150K-TA
Philips PMBD6050 USA [phone] USA [phone]
Sumida CD43150
USA [phone]
Japan [phone]
TDK NLC453232T-150K
USA [phone]
Japan [phone]
USA [phone]
USA [phone]
USA [phone]
Japan [phone]
USA [phone]
Japan [phone]
USA [phone]
Japan [phone]
USA [phone]
Japan [phone]