MAX221ECUE+T Maxim Integrated Products, MAX221ECUE+T Datasheet - Page 5
![IC TXRX RS-232 5V 16-TSSOP](/photos/6/56/65666/175-16-tssop_sml.jpg)
MAX221ECUE+T
Manufacturer Part Number
MAX221ECUE+T
Description
IC TXRX RS-232 5V 16-TSSOP
Manufacturer
Maxim Integrated Products
Type
Transceiverr
Datasheet
1.MAX221CUE.pdf
(8 pages)
Specifications of MAX221ECUE+T
Number Of Drivers/receivers
1/1
Protocol
RS232
Voltage - Supply
4.5 V ~ 5.5 V
Mounting Type
Surface Mount
Package / Case
16-TSSOP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
The MAX221’s internal power supply consists of a dual
charge pump that provides a positive output voltage
(doubling charge pump) and a negative voltage (invert-
ing charge pump) from a single +5V supply. The
charge pumps operate in continuous mode. Each
charge pump requires a flying capacitor (C1, C2) and a
reservoir capacitor (C3, C4) to generate the V+ and V-
supplies.
The transmitter is an inverting level translator that con-
verts CMOS-logic levels to 5.0V EIA/TIA-232 levels. It
guarantees a 250kbps data rate with worst-case loads
of 3kΩ in parallel with 1000pF.
When FORCEOFF is driven to ground, or when the
AutoShutdown circuitry senses invalid voltage levels on
the receiver input, the transmitter is disabled and the out-
put is forced into a high-impedance state. The transmitter
input does not have a pull-up resistor.
The MAX221’s receiver converts RS-232 signals to
CMOS-logic output levels. The receiver has an inverting
Figure 1. Shutdown Current Test Circuit
_______________Detailed Description
C
BYPASS
0.1 F
0.1 F
C1
C2
Dual Charge-Pump Voltage Converter
+5V
0.1 F
12
11
I
2
4
5
6
9
SHDN
1
TIN
C1+
C1-
C2-
C2+
ROUT
EN
FORCEON
_______________________________________________________________________________________
MAX221
GND
V
CC
+5V, 1µA, Single RS-232 Transceiver
15
14
RS-232 Transmitter
FORCEOFF
INVALID
RS-232 Receiver
5k
TOUT 13
RIN 8
V+
V-
3
7
10
16
TO POWER-
MANAGEMENT
UNIT
C3
0.1 F
C4
0.1 F
3k
three-state output and can be active or inactive. In shut-
down (FORCEOFF = low) or in AutoShutdown, the
receiver is active (Table 1). Drive EN high to place the
receiver in a high-impedance state. The receiver is high
impedance when the MAX221 is in shutdown (FORCE-
OFF = low).
The MAX221’s INVALID output is pulled low when no
valid RS-232 signal level is detected on the receiver
input. INVALID is functional in any mode (Figures 2
and 3).
The MAX221 achieves 1µA supply current with Maxim’s
AutoShutdown feature, which operates when FORCEON
is low and FORCEOFF is high. When the device senses
no valid signal levels on the receiver input for 30µs, the
on-board charge pump and driver are shut off, reducing
supply current to 1µA. This occurs if the RS-232 cable is
disconnected or the connected peripheral transmitter is
turned off. The MAX221 turns on again when a valid
level is applied to the RS-232 receiver input. As a result,
the system saves power without changes to the existing
BIOS or operating system.
Table 1 and Figure 2c summarize the MAX221 operat-
ing modes. FORCEON and FORCEOFF override
AutoShutdown. When neither control is asserted, the
device selects between these states automatically,
based on the receiver input level. Figures 2a, 2b, and
3a depict valid and invalid RS-232 receiver levels.
Figure 3 shows the input levels and timing diagram for
AutoShutdown operation.
A device or another system with AutoShutdown con-
nected to the MAX221 may need time to wake up.
Figure 4 shows a circuit that forces the transmitter on
for 100ms, allowing enough time for the other system to
realize that the MAX221 is awake. If the other system
transmits valid RS-232 signals within that time, the RS-
232 ports on both systems remain enabled.
When shut down, the device’s charge pumps are off,
V+ is pulled to V
transmitter output is high impedance. The time required
to exit shutdown is typically 100µs (Figure 3b).
For direct software control, use INVALID to indicate a
DTR or Ring Indicator signal. Connect FORCEOFF and
FORCEON together to disable AutoShutdown so the
line acts like a SHDN input.
with AutoShutdown
Software-Controlled Shutdown
CC
, V- is pulled to ground, and the
AutoShutdown
5