ICL3224 Intersil, ICL3224 Datasheet - Page 11

• Manufacturer Part Number: ICL3224
• Description: 1 Microamp/ +3V to +5.5V/ 250kbps/ RS-232 Transceivers with Enhanced Automatic Powerdown
• Manufacturer: Intersil

reattached, connect FORCEON to FORCEOFF through a
network similar to that shown in Figure 5.
Ready Output (ICL3224 and ICL3226 only)
The Ready output indicates that the ICL322X is ready to
transmit. Ready switches low whenever the device enters
powerdown, and switches back high during power-up when
V- reaches -4V or lower.
Capacitor Selection
The charge pumps require 0.1µF capacitors for 3.3V
operation. For other supply voltages refer to Table 3 for
capacitor values. Do not use values smaller than those listed
in Table 3. Increasing the capacitor values (by a factor of 2)
reduces ripple on the transmitter outputs and slightly
reduces power consumption. C
increased without increasing C
increase C
maintain the proper ratios (C
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-.
NOTE:
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 10 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.
Operation Down to 2.7V
8. Parenthesized values apply only to the ICL3238
3.0 to 3.6 (3.3V ±10%)
3.15 to 3.6 (3.3V ±5%)
TABLE 3. REQUIRED CAPACITOR VALUES (Note 8)
4.5 to 5.5
3.0 to 5.5
V
CC
1
(V)
without also increasing C
0.1 (0.22)
0.1 (0.22)
C
0.047
(0.1)
1
11
1
(µF)
to the other capacitors).
1
2
’s value, however, do not
CC
, C
3
to ground with a
, and C
2
, C
ICL3224, ICL3226, ICL3238, ICL3244
3
C
, and C
4
2
, C
can be
0.1 (0.22)
0.47 (1.0)
(0.1)
0.33
3
, C
4
4
to
(µF)
1
.
ICL32XX transmitter outputs meet RS-562 levels (
the full data rate, with V
typically ensure interoperability with RS-232 devices.
Mouse Driveability
The ICL3244 is specifically designed to power a serial
mouse while operating from low voltage supplies. Figure 11
shows the transmitter output voltages under increasing load
current. The on-chip switching regulator ensures the
transmitters will supply at least
conditions (15mA for paralleled V+ transmitters, 7.3mA for
single V- transmitter).
High Data Rates
The ICL32XX maintain the RS-232
output voltages even at high data rates. Figure 12 details a
transmitter loopback test circuit, and Figure 13 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 14 shows the loopback results
5V/DIV
2V/DIV
FIGURE 11. TRANSMITTER OUTPUT VOLTAGE vs LOAD
FIGURE 10. TRANSMITTER OUTPUTS WHEN EXITING
5V/DIV
-1
-2
-3
-4
-5
-6
6
5
4
3
2
1
0
0
V
CC
1
CURRENT (PER TRANSMITTER, i.e., DOUBLE
CURRENT AXIS FOR TOTAL V
POWERDOWN
FORCEOFF
LOAD CURRENT PER TRANSMITTER (mA)
V
T1
T2
T3
CC
2
= 3.0V
READY
3
V
ICL3244
V
CC
OUT
OUT
TIME (20µs/DIV.)
4
as low as 2.7V. RS-562 levels
+
-
±
5
5V during worst case
±
5V minimum transmitter
6
7
OUT+
V
C1 - C4 = 0.1µF
V
V
CC
OUT
OUT
8
CURRENT)
= +3.3V
+
-
±
T2
T1
3.7V), at
9
10