Datasheet

MAX3320A/B/L/T
3V to 5.5V, up to 250kbps True RS-232 Transceiver
with 4µA AutoShutdown Plus and Power-On Reset
8 _______________________________________________________________________________________
__________Applications Information
Ensuring a Valid Reset Output
Down to V
CC
= 0V
When V
CC
falls below 1V, RESET no longer sinks cur-
rent: it becomes an open circuit. Therefore, high-
impedance CMOS logic inputs connected to RESET
can drift to undefined voltages. This presents no prob-
lem in most applications, since most µPs and other cir-
cuitry is inoperative with V
CC
below 1V. However, in
applications where RESET must be valid down to 0V,
add a pull-down resistor to ground, holding RESET low
(Figure 4). R1’s value is not critical; 100kΩ is large
enough not to load RESET, and small enough to pull it
to ground.
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; use either polarized or nonpolarized
capacitors. The charge pump requires 0.1µF capaci-
tors for 3.3V operation. For other supply voltages, refer
to Table 3 for required capacitor values. Do not use val-
ues smaller than those listed in Table 3. 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 C2, C3, C4,
and C
BYPASS
, to maintain the proper ratios (C1 to
the other capacitors).
RECEIVER INPUT LEVELS
-2.7V
-0.3V
2.7V
0.3V
0V
INDETERMINATE
INVALID HIGH
INVALID LOW
INVALID HIGH
INDETERMINATE
Figure 3b. Receiver Positive/Negative Thresholds for INVALID
Figure 3a. AutoShutdown Plus and INVALID Timing Diagram
V
CC
0
V+
V-
V
CC
0
INVALID
OUTPUT
* ALL RECEIVER/TRANSMITTER INPUTS INACTIVE
** ANY ONE RECEIVER/TRANSMITTER INPUT BECOMES ACTIVE FORCEON = GND, FORCEOFF = V
CC
TRANSMITTER
INPUTS
VOLTAGE
RECEIVER
INPUTS
VOLTAGE
TRANSMITTER
OUTPUTS
VOLTAGE
t
AUTOSHDN
INVALID
REGION
* **
t
WU
t
WU
I
NVL
t
AUTOSHDN