Datasheet

on the transmitter outputs and slightly reduces power
consumption. The values of C2, C3, and C4 can be
increased without changing C1’s value. However, do
not increase C1’s value without also increasing the val-
ues of C2, C3, and C4 to maintain the proper ratios (C1
to the other capacitors).
When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperature. If in doubt, use capaci-
tors with a larger nominal value. The capacitor’s equiv-
alent series resistance (ESR), which usually rises at low
temperatures, influences the amount of ripple on V+
and V-.
Multidrop Applications
The MAX3323E connects to the RS-232 serial port of
computer peripherals such as a bar-code scanner,
video security controls, industrial multimeters, etc., and
allows multiple devices to share the same communica-
tion cable connected to a PC.
Figure 9 shows a PC UART transmitting to a single
receiver with a 5kΩ termination resistor while the other
receivers remain in a high-impedance state. When the
receiver inputs are high impedance, they remain active
and maintain receiving capability. This feature permits
the design of multidrop applications, which observe the
RS-232 interface standard.
Transmitters are enabled and disabled through
TXENABLE, allowing the sharing of a single bus line.
Transmitters are high impedance when disabled. The
host PC’s transmitter stays enabled at all times. Only
one peripheral transmitter remains enabled at any time.
If the host PC wants to communicate with another
peripheral, it first must tell the current peripheral to
deassert its transmitter.
MAX3322E/MAX3323E
±15kV ESD-Protected, RS-232 Transceivers for
Multidrop Applications
_______________________________________________________________________________________ 9
MAX3323E
PC
UART
5kΩ
PERIPHERAL
CONTROL WITH UART
MAX3323E
5kΩ
PERIPHERAL
CONTROL WITH UART
MAX3323E
5kΩ
PERIPHERAL
CONTROL WITH UART
Figure 9. Multidrop Application
V
CC
(V) C1 (µF)
C2, C3, C4 (µF)
3.0 to 3.6 0.1 0.1
4.5 to 5.5 0.047 0.33
3.0 to 5.5 0.22 1
Table 2. Minimum Required Capacitor
Values