XR32330 Datasheet, PDF (10/13 Pages) Exar Corporation – 3-Driver/3-Receiver Intelligent RS-232 Transceiver

XR32330
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 XR32330
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 XR32330 devices have a patent pending AUTO ON-
LINE® circuitry on board that saves power in applications
such as hand held and portable systems.
The XR32330 devices incorporate an AUTO ON-LINE® cir-
cuit 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-
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 (see Figure 9), 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 disabled and the device goes into a shutdown or
standby mode. When ONLINE is HIGH, the AUTO ON-
LINE® mode is disabled.
RS-232
Receiver
Input
Voltage
Invalid
Region
STATUS
RS-232
Driver
Output
Voltage
V+
Charge
Pump
V-
tSTSL
tOFF L IN E
tSTSH
tONLINE
+5V
-5V
VC C
0V
Figure 9: 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 XR32330 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 XR32330 driver
and receiver outputs can be found in Table 3 on page 11.
The STATUS pin outputs a logic LOW signal if no valid RS-
232 level is detected at either of the receiver inputs. This
pin goes to a logic HIGH when the external transmitters are
enabled and the cable is connected providing valid RS-232
voltage levels to the receiver input pins R1IN, R2IN and
R3IN.
When the XR32330 is shut down, the charge pumps are
turned off. V+ charge pump output decays to V_CC, the V-
output decays to GND, see Figure 9. The decay time will
depend on the size of capacitors used for the charge pump.
Once in shutdown, the time required to exit the shut down
state and have valid V+ and V- levels is typically 30μs.
For easy programming, the STATUS can be used to indi-
cate DSR or a Ring Indicator signal. Tying ONLINE and
SHUTDOWN together will bypass the AUTO ON-LINE® cir-
cuitry so this connection acts like a shutdown input pin.
June 16, 2016
10 / 13
exar.com/XR32330
Rev 1B