ICL3224E_14 Datasheet, PDF (13/20 Pages) Intersil Corporation – +/-15kV ESD Protected, +3V to +5.5V, 1Microamp, 250kbps, RS-232 Transceivers with Enhanced Automatic Powerdown

ICL3224E, ICL3226E, ICL3244E
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-.
TABLE 3. REQUIRED CAPACITOR VALUES
V_CC
(V)
C₁
C₂, C₃, C₄
(µF)
(µF)
3.0 to 3.6
0.1
0.1
4.5 to 5.5
0.047
0.33
3.0 to 5.5
0.1
0.47
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.
Operation Down to 2.7V
ICL32XXE transmitter outputs meet RS-562 levels (±3.7V),
at full data rate, with V_CC as low as 2.7V. RS-562 levels
typically ensure inter operability with RS-232 devices.
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.
5V/DIV.
FORCEOFF
2V/DIV.
T1
V_CC = +3.3V
C1 - C4 = 0.1µF
T2
5V/DIV.
READY
TIME (20µs/DIV.)
FIGURE 10. TRANSMITTER OUTPUTS WHEN EXITING
POWERDOWN
Mouse Driveability
The ICL3244E 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 ±5V during worst case
conditions (15mA for paralleled V+ transmitters, 7.3mA for
single V- transmitter).
6
5
4
V_OUT+
3
2
V_CC = 3.0V
1
T1
0
-1
T2
-2
-3
-4 ^{VCC T3}
V_OUT+
ICL3244E
V_OUT -
V_OUT -
-5
-6
0 1 2 3 4 5 6 7 8 9 10
LOAD CURRENT PER TRANSMITTER (mA)
FIGURE 11. TRANSMITTER OUTPUT VOLTAGE vs LOAD
CURRENT (PER TRANSMITTER, i.e., DOUBLE
CURRENT AXIS FOR TOTAL V_OUT+ CURRENT)
High Data Rates
The ICL32XXE maintain the RS-232 ±5V minimum
transmitter 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 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-
ICL32XXE
C2+
V-
C2-
T_IN
T_OUT
R_OUT
R_IN
FORCEON
5K
FORCEOFF
+
C₃
+C⁴
1000pF
FIGURE 12. TRANSMITTER LOOPBACK TEST CIRCUIT
13