MAX3221E View Datasheet(PDF) - Maxim Integrated
Part Name
Description
MFG CO.
MAX3221E
Maxim Integrated
'MAX3221E' PDF : 19 Pages View PDF
MAX3221E/MAX3223E/MAX3243E
±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,
RS-232 Transceivers with AutoShutdown
RS-232 Receivers
The MAX3221E/MAX3223E/MAX3243E’s receivers con-
vert RS-232 signals to CMOS-logic output levels. All
receivers have inverting three-state outputs and can be
active or inactive. In shutdown (FORCEOFF = low) or in
AutoShutdown, the MAX3221E/MAX3223E’s receivers
are active (Table 1). Drive EN high to place the receiv-
er(s) in a high-impedance state. The MAX3243E’s
receivers are high-impedance when the part is in shut-
down (FORCEOFF = low).
The MAX3243E features an extra, always-active com-
plementary output (R2OUTB). R2OUTB monitors
receiver activity while the other receivers are high-
impedance. This allows Ring Indicator to be monitored
without forward biasing other devices connected to the
receiver outputs. This is ideal for systems where VCC
drops to 0 in shutdown to accommodate peripherals
such as UARTs (Figure 2).
The MAX3221E/MAX3223E/MAX3243E feature an
INVALID output that is enabled low when no valid RS-232
signal levels have been detected on all receiver inputs.
INVALID is functional in any mode (Figures 3 and 5).
AutoShutdown
The MAX3221E/MAX3223E/MAX3243E achieve a 1µA
supply current with Maxim’s new AutoShutdown fea-
ture, which operates when FORCEON is low and
FORCEOFF is high. When these devices sense no valid
signal levels on all receiver inputs for 30µs, the on-
board charge pump and drivers are shut off, reducing
supply current to 1µA. This occurs if the RS-232 cable
is disconnected or the connected peripheral transmit-
ters are turned off. The device turns on again when a
valid level is applied to any RS-232 receiver input. As a
result, the system saves power without changes to the
existing BIOS or operating system.
Table 2 and Figure 3c summarize the MAX3221E/
MAX3223E/MAX3243E operating modes. FORCEON
and FORCEOFF override AutoShutdown. When neither
control is asserted, the IC selects between these states
automatically, based on receiver input levels. Figures
3a, 3b, and 5a depict valid and invalid RS-232 receiver
levels. Figure 5 shows the input levels and timing dia-
gram for AutoShutdown operation.
VCC
PROTECTION
DIODE
VCC
Rx
I
UART
Tx
GND
SHDN = GND
PREVIOUS
RS-232
5kΩ
a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.
VCC
TO LOGIC
µP TRANSITION
DETECTOR
PROTECTION
DIODE
I
R2OUTB
VCC
Rx
UART
R2OUT
THREE-STATED
Tx
GND
T1IN
FORCEOFF = GND
MAX3243E
R2IN
5kΩ
T1OUT
b) NEW MAX3243E: IN SHUTDOWN, R2OUTB IS USED TO MONITOR EXTERNAL
DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT PATH
THROUGH THE UART'S PROTECTION DIODE.
Figure 2. The MAX3243E detects RS-232 activity when the
UART and interface are shut down.
8
Maxim Integrated
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