MAX3316–MAX3319
2.5V, 1µA, 460kbps,
RS-232-Compatible Transceivers
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When shut down, the device’s charge pumps turn off,
V+ is pulled to V
CC
, V- is pulled to ground, the transmitter
outputs are high impedance, and READY is driven low.
The time required to exit shutdown is typically 30µs
(Figure 2).
By connecting FORCEON to INVALID, the MAX3318/
MAX3319 shut down when no valid receiver level is
detected and wake up when a valid receiver level is
detected.
A system with AutoShutdown Plus may need time to
wake up. Figure 5 shows a circuit that forces the trans-
mitters on for 100ms, allowing enough time for the other
system to realize that the MAX3318/MAX3319 is awake.
If the other system outputs valid RS-232 signal transi-
tions within that time, the RS-232 ports on both systems
remain enabled.
Connecting to the PC
(MAX3318/MAX3319)
If direct software control is desired, use INVALID to
indicate DTR or ring indicator (RI) signal. This can be
used to connect a hand-held device to a PC. One
example is using the hot sync function on a personal
digital assistant (PDA). The transmitter and receiver
signals (T_OUT and R_IN) are used for communication,
while INVALID causes a change of state on RI. The
change of state on RI will trigger an interrupt on the PC
and allow communication to begin between the device
and the PC. This eliminates the need for the PC to poll
constantly the receiver or transmitter lines to determine
if the device is connected.
Applications Information
RS-232-Compatible Operation
The MAX3316–MAX3319 do not meet EIA-232 require-
ments for transmitter output voltage levels. EIA-232 com-
pliance specifies transmitter output voltage swings of
±5V when loaded with 3kΩ and 2500pF.
The receiver inputs are fully EIA-232 compliant.
The MAX3316–MAX3319 will function properly with most
modern RS-232 interfaces. This allows RS-232-compati-
ble communication in low-voltage systems without the
added expense of a voltage tripler or switched-mode
power supply.
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. The charge pump requires 0.1µF capaci-
tors. Increasing the capacitor values (e.g., by a factor of
2) reduces ripple on the transmitter outputs and slightly
reduces power consumption. C2, C3, and C4 can be
increased without changing C1’s value. However, do
not increase C1 without also increasing the values of
