Datasheet

MAX3320A/B/L/T
3V to 5.5V, up to 250kbps True RS-232 Transceiver
with 4µA AutoShutdown Plus and Power-On Reset
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When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperatures outside the 0°C to +70°C
range. If in doubt, use capacitors with a larger nominal
value. The capacitor's equivalent series resistance
(ESR), which usually rises at low temperatures, influ-
ences the amount of ripple on V+ and V-.
Transmitter Outputs
when Exiting Shutdown
Figure 5 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans-
mitter outputs go to opposite RS-232 levels (one trans-
mitter input is high; the other is low). Each transmitter is
loaded with 3kΩ in parallel with 2500pF. The transmitter
outputs display no ringing or undesirable transients as
they exit shutdown. Note that the transmitters are
enabled only when the magnitude of V- exceeds
approximately 3V.
High Data Rates
The MAX3320 maintains the RS-232 ±5V minimum
transmitter output voltage even at high data rates.
Figure 6 shows a transmitter loop-back test circuit.
Figure 7 shows a loop-back test result at 120kbps, and
Figure 8 shows the same test at 250kbps. For Figure 7,
both transmitters were driven simultaneously at
120kbps into RS-232 loads in parallel with 1000pF. For
Figure 8, a single transmitter was driven at 250kbps,
and both transmitters were loaded with an RS-232
receiver in parallel with 1000pF.
Interconnection with 3V and 5V Logic
The MAX3320 can directly interface with various 5V
logic families, including ACT and HCT CMOS. See
Table 4 for more information on possible combinations
of interconnections.
V
CC
= 3.3V
C1 - C4 = 0.1µF
5µs/div
2V/div
2V/div
T2OUT
T1OUT
FORCEON =
FORCEOFF
Figure 5. Transmitter Outputs when Exiting Shutdown or
Powering Up
MAX3320
5k
R_ IN
R_ OUT
C2-
C2+
C1-
C1+
V-
V+
V
CC
C4
C3*
C1
C2
V
CC
FORCEOFF
T_ OUT
T_ IN
GND
V
CC
*C3 CAN BE RETURNED TO
V
CC
OR GND.
FORCEON
1000pF
Figure 6. Loop-Back Test Circuit
MAX3320
GND
100k
V
CC
V
CC
RESET
Figure 4. Ensuring RESET Valid to V
CC
= 0V
0.1 0.473 to 5.5
0.047 0.334.5 to 5.5
C1
(µF)
0.1
C2, C3, C4, C
BYPASS
(µF)
0.1
V
CC
(V)
3 to 3.6
Table 3. Required Minimum
Capacitance Values