ISL83384E Intersil Corporation, ISL83384E Datasheet - Page 6

• Manufacturer Part Number: ISL83384E
• Description: 15kV ESD Protected/ +3V to +5.5V/ 1 Microamp/ 250Kbps/ RS-232 Transmitter/Receiver
• Manufacturer: Intersil Corporation

Capacitor Selection
The charge pumps require 0.1µF or greater capacitors for
operation with 3.3V ≤ V
values (by a factor of 2) reduces ripple on the transmitter
outputs and slightly reduces power consumption. C
and C
however, do not increase C
and C
capacitors).
When using minimum required capacitor values, make sure
that capacitor values do not degrade excessively with
temperature. If in doubt, use capacitors with a larger nominal
value. The capacitor’s equivalent series resistance (ESR)
usually rises at low temperatures and it influences the
amount of ripple on V+ and V-.
Operation Down to 2.7V
ISL83384E transmitter outputs meet RS-562 levels (
at the full data rate, with V
typically ensure inter operability with RS-232 devices.
Power Supply Decoupling
In most circumstances a 0.1µF bypass capacitor is
adequate. In applications that are particularly sensitive to
power supply noise, decouple V
capacitor of the same value as the charge-pump capacitor C
Connect the bypass capacitor as close as possible to the IC.
Transmitter Outputs when Exiting
Powerdown
Figure 5 shows the response of two transmitter outputs
when exiting powerdown mode. As they activate, the two
transmitter outputs properly go to opposite RS-232 levels,
with no glitching, ringing, nor undesirable transients. Each
transmitter is loaded with 3kΩ in parallel with 2500pF. Note
that the transmitters enable only when the magnitude of the
supplies exceed approximately 3V.
5V/DIV.
2V/DIV.
FIGURE 5. TRANSMITTER OUTPUTS WHEN EXITING
4
4
can be increased without increasing C
to maintain the proper ratios (C
V
C1 - C4 = 0.1µF
CC
= +3.3V
POWERDOWN
SHDN
CC
CC
TIME (20µs/DIV.)
≤ 5.5V. Increasing the capacitor
1
without also increasing C
as low as 2.7V. RS-562 levels
6
CC
to ground with a
1
to the other
1
’s value,
T1
T2
2
, C
±
3.7V),
2
3
, C
,
ISL83384E
3
1
,
.
High Data Rates
The ISL83384E maintains the RS-232
transmitter output voltages even at high data rates. Figure 6
details a transmitter loopback test circuit, and Figure 7
illustrates the loopback test result at 120Kbps. For this test,
all transmitters were simultaneously driving RS-232 loads in
parallel with 1000pF, at 120Kbps. Figure 8 shows the
loopback results for a single transmitter driving 1000pF and
an RS-232 load at 250Kbps. The static transmitter was also
loaded with an RS-232 receiver.
5V/DIV.
R1
T1
T1
OUT
OUT
FIGURE 6. TRANSMITTER LOOPBACK TEST CIRCUIT
IN
V
V
C
C
CC
CC
1
2
V
C1 - C4 = 0.1µF
+
+
CC
FIGURE 7. LOOPBACK TEST AT 120Kbps
= +3.3V
0.1µF
C1+
C1-
C2+
C2-
T
R
SHDN
IN
OUT
+
ISL83384E
V
CC
5µs/DIV.
T
OUT
R
V+
5k
±
V-
IN
5V minimum
+
+
C
C
1000pF
3
4