_______________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.
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 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 1Ω 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
MAX3212
+2.7V to +3.6V-Powered, 1µA Supply Current,
3-Driver/5-Receiver, True RS-232 Transceiver
_______________________________________________________________________________________ 5
______________________________________________________________Pin Description
PIN NAME FUNCTION
1 LN Inductor/Diode Connection Point
2 LP Inductor/Diode Connection Point
3 V
CC
Supply Voltage Input, 2.7V to 3.6V
4 EN
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.
5 TRAN
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.
6 INVALID
Output of Invalid Signal Detector. Low if invalid RS-232 levels are present on all
receiver inputs, otherwise high.
7 R5OUTB Complementary Output of R5OUT—always active
8–12 R1OUT–R5OUT Receiver Outputs. Swing from GND to V
CC
. High-impedance when EN is low.
13, 14, 15 T1IN, T2IN, T3IN Transmitter Inputs
16 V- Negative Supply generated on-board
17, 18, 19 T3OUT, T2OUT, T1OUT Transmitter Outputs
20–24 R5IN–R1IN Receiver Inputs
25 FORCEOFF
Drive low to shut down transmitters and on-board power supply, overriding all automatic
circuitry and FORCEON (see Figure 3).
26 FORCEON
Drive high to overide automatic circuitry, keeping transmitters on (see Figure 3).
FORCEOFF = high.
27 V+ Positive Supply generated on-board
28 GND Ground
