MAX221EEAE+ Maxim Integrated Products, MAX221EEAE+ Datasheet - Page 5

• Manufacturer Part Number: MAX221EEAE+
• Description: IC TXRX RS-232 5V 16-SSOP
• Manufacturer: Maxim Integrated Products
• Type: Transceiverr

Specifications of MAX221EEAE+

• Number Of Drivers/receivers: 1/1
• Protocol: RS232
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Propagation Delay Time Ns: 0.15 ms
• Operating Supply Voltage: 5 V
• Supply Current: 5 mA
• Operating Temperature Range: - 40 C to + 85 C
• Data Rate: 250 Kbps
• Mounting Style: SMD/SMT
• Number Of I/os: 1 / 1
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX221E’s internal power supply consists of a
dual charge pump that provides a positive output volt-
age (doubling charge pump) and negative output volt-
age (inverting 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 3k 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
output is forced into a high-impedance state. The trans-
mitter input does not have a pull-up resistor.
Figure 1. Shutdown Current Test Circuit
_______________Detailed Description
C
BYPASS
±15kV ESD-Protected, +5V, 1µA, Single RS-232
0.1 F
0.1 F
0.1 F
C2
C1
Dual Charge-Pump Voltage Converter
+5V
12
11
6
9
2
4
5
1
TIN
C1+
C1-
C2-
C2+
ROUT
EN
FORCEON
I
SHDN
_______________________________________________________________________________________
MAX221E
GND
V
CC
15
14
RS-232 Transmitter
FORCEOFF
INVALID
5k
TOUT 13
RIN 8
V+
V-
Transceiver with AutoShutdown
3
7
10
16
TO POWER-
MANAGEMENT
UNIT
C3
0.1 F
C4
0.1 F
3k
The MAX221E’s receiver converts RS-232 signals to
CMOS-logic output levels. The receiver has an inverting
three-state output and can be active or inactive. In
shutdown (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 MAX221E is in shutdown
(FORCEOFF = low).
The MAX221E’s INVALID output is pulled low when
there is no valid RS-232 signal level detected on the
receiver input. INVALID is functional in any mode
(Figures 2 and 3).
The MAX221E 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 con-
nected peripheral transmitter is turned off. The
MAX221E 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 MAX221E 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 MAX221E 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 MAX221E 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 turn off,
V+ is pulled to V
transmitter output is high impedance. The time required
to exit shutdown is typically 100µs (Figure 3b).
CC
, V- is pulled to ground, and the
RS-232 Receiver
AutoShutdown
5