XR32430EUCRTR-F Datasheet, PDF (10/14 Pages) Exar Corporation – 3-Driver/5-Receiver Intelligent RS-232 Transceiver with 1.65V-5.5V Interface

XR32430/XR32431
The charge pump operates with 0.1μF capacitors for 3.3V
operation. For other supply voltages, see the table for
required capacitor values. Do not use values smaller than
those listed. Increasing the capacitor values (e.g., by dou-
bling in value) reduces ripple on the transmitter outputs and
may slightly reduce power consumption. C2, C3, and C4
can be increased without changing C1’s value.
LINE® function is active. Once active, the device is enabled
until there is no activity on the receiver inputs. The receiver
input typically sees at least +3V, which are generated from
the transmitters at the other end of the cable with a +5V
minimum.
When the external transmitters are disabled or the cable is
disconnected, the receiver inputs will be pulled down by
their internal 5kΩ resistors to ground. When this occurs
over a period of time, the internal transmitters will be dis-
abled and the device goes into a shutdown or standby
mode. When ONLINE is HIGH, the AUTO ON-LINE® mode
is disabled.
Table 1:
Minimum Recommended Charge Pump
Capacitor Values
Supply Voltage
V_CC
3.0V to 3.6V
4.5V to 5.5V
3.0V to 5.5V
Charge Pump Capacitor
Value for XR32430/31
C1 - C4 = 0.1F
C1 = 0.047F,
C2 - C4 = 0.33F
C1 - C4 = 0.22F
For best charge pump efficiency locate the charge pump
and bypass capacitors as close as possible to the IC. Sur-
face mount capacitors are best for this purpose. Using
capacitors with lower equivalent series resistance (ESR)
and self-inductance, along with minimizing parasitic PCB
trace inductance will optimize charge pump operation.
Designers are also advised to consider that capacitor val-
ues may shift over time and operating temperature.
AUTO ON-LINE® Circuitry
The XR32430/31 devices have a patent pending AUTO
ON-LINE® circuitry on board that saves power in applica-
tions such as laptop computers, palmtop (PDA) computers
and other portable systems.
The XR32430/31 devices incorporate an AUTO ON-LINE®
circuit that automatically enables itself when the external
transmitters are enabled and the cable is connected. Con-
versely, the AUTO ON-LINE® circuit also disables most of
the internal circuitry when the device is not being used and
goes into a standby mode where the device typically draws
1μA. This function is externally controlled by the ONLINE
pin. When this pin is tied to a logic LOW, the AUTO ON-
RS-232
Receiver
Input
Voltage
Invalid
Region
STATUS
RS-232
Driver
Output
Voltage
V+
Charge
Pump
V-
tSTSL
tOFF LIN E
tSTSH
tON LIN E
+5V
-5V
VCC
0V
Figure 11: Auto On-Line Timing
The STATUS pin goes to a logic LOW when the cable is dis-
connected or the external transmitters are disabled.
When the XR32430/31 drivers and internal charge pump
are disabled, the supply current is reduced to 1μA. This can
commonly occur in hand-held or portable applications
where the RS-232 cable is disconnected or the RS-232
drivers of the connected peripheral are turned off.
The AUTO ON-LINE® mode can be disabled by the SHUT-
DOWN pin. If this pin is a logic LOW, the AUTO ON-LINE®
function will not operate regardless of the logic state of the
ONLINE pin. The truth table logic of the XR32430/31 driver
and receiver outputs can be found in Table 3 on page 11.
The STATUS pin outputs a logic LOW signal if the no valid
RS-232 level is detected at either of the receiver inputs.
This pin goes to a logic HIGH when the external transmit-
ters are enabled and the cable is connected providing valid
RS-232 voltage levels to all the RxIN receiver input pins.
© 2014 Exar Corporation
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