Datasheet

MAX3387E
Power-Supply Decoupling
In most circumstances, a 0.1µF bypass capacitor is ade-
quate. In applications that are sensitive to power-supply
noise, decouple V
CC
to ground with a capacitor of the
same value as charge-pump capacitor C1. Connect
bypass capacitors as close to the IC as possible.
Operation Down to 2.7V
Transmitter outputs will meet TIA/EIA-562 levels of
±3.7V with supply voltages as low as +2.7V.
Transmitter Outputs when
Exiting Shutdown
Figure 7 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans-
mitter outputs are shown going to opposite RS-232 lev-
els (one transmitter input is high; the other is low). Each
transmitter is loaded with 3kΩ in parallel with 2500pF.
The transmitter outputs display no ringing or undesir-
able transients as they come out of shutdown. Note that
the transmitters are enabled only when the magnitude
of V- exceeds approximately 3V.
High Data Rates
The MAX3387E maintains the RS-232 ±5.0V minimum
transmitter output voltage even at high data rates.
Figure 8 shows a transmitter loopback test circuit.
Figure 9 shows a loopback test result at 120kbps, and
Figure 10 shows the same test at 250kbps. For Figure
9, all transmitters were driven simultaneously at
120kbps into RS-232 loads in parallel with 1000pF. For
Figure 10, a single transmitter was driven at 250kbps,
and all transmitters were loaded with an RS-232 receiv-
er in parallel with 1000pF.
Interconnection with
3V and 5V Logic
The MAX3387E can directly interface with various 5V
logic families, including ACT and HCT CMOS. The logic
voltage power-supply pin (V
L
) sets the output voltage
level of the receivers and the input thresholds of the
transmitters.
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
12 ______________________________________________________________________________________
MAX3387E
5k
R_ IN
R_ OUT
C2-
C2+
C1-
C1+
V-
V+
V
CC
C4
C3
C1
C2
0.1μF
V
CC
FORCEON
FORCEOFF
T_ OUT
T_ IN
GND
V
CC
1000pF
Figure 8. Loopback Test Circuit
2μs/div
T1IN
T1OUT
R1OUT
5V/div
5V/div
5V/div
V
CC
= 3.3V
Figure 9. Loopback Test Results at 120kbps
50μs/div
T2
T1
5V/div
2V/div
V
CC
= 3.3V
C1–C4 = 0.1μF
Figure 7. Transmitter Outputs when Exiting Shutdown