ICL3310 Datasheet, PDF (6/9 Pages) Intersil Corporation – +3V to +5.5V, 1 Microamp, 250kbps, RS-232 Transmitter/Receiver

ICL3310
PWR
MGT
LOGIC
SHDN
5V/DIV.
SHDN
T1
ICL3310
2V/DIV.
CPU
I/O
UART
FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN
Capacitor Selection
The charge pumps require 0.1µF or greater capacitors for
operation with 3.3V ≤ V_CC ≤ 5.5V. Increasing the capacitor
values (by a factor of 2) reduces ripple on the transmitter
outputs and slightly reduces power consumption. C₂, C₃, and
C₄ can be increased without increasing C₁’s value, however,
do not increase C₁ without also increasing C₂, C₃, and C₄ to
maintain the proper ratios (C₁ to the other 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-.
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_CC to ground with a
capacitor of the same value as the charge-pump capacitor C₁.
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.
T2
V_CC = +3.3V
C1 - C4 = 0.1µF
TIME (20µs/DIV.)
FIGURE 5. TRANSMITTER OUTPUTS WHEN EXITING
POWERDOWN
High Data Rates
The ICL3310 maintain the RS-232 ±5V minimum 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 transmitters were also loaded with an
RS-232 receiver.
V_CC
0.1µF
+
+
C₁
+
C₂
V_CC
C1+
V_CC
V+
C1-
ICL3310
C2+
V-
C2-
T_IN
T_OUT
R_OUT
R_IN
5k
SHDN
+
C₃
+C⁴
1000pF
FIGURE 6. TRANSMITTER LOOPBACK TEST CIRCUIT
6