ICL3243EIA Datasheet, PDF (18/33 Pages) Intersil Corporation – ±15kV ESD Protected, +3V to +5.5V, 1μA, 250kbps, RS-232 Transmitters/Receivers

ICL3221E, ICL3222E, ICL3223E, ICL3232E, ICL3241E, ICL3243E
Devices with the automatic power-down feature include
an INVALID output signal, which switches low to indicate
that invalid levels have persisted on all of the receiver
inputs for more than 30µs (see Figure 7). INVALID
switches high 1µs after detecting a valid RS-232 level on
a receiver input. INVALID operates in all modes (forced
or automatic power-down, or forced on), so it is also
useful for systems employing manual power-down
circuitry. When automatic power-down is utilized,
INVALID = 0 indicates that the ICL32xxE is in
power-down mode.
The time to recover from automatic power-down mode is
typically 100µs.
RECEIVER
INPUTS
INVALID
} _REGION
TRANSMITTER
OUTPUTS
INVALID ^VCC
OUTPUT ₀
V+
t_INVL
AUTOPWDN
t_INVH
PWR UP
V_CC
0
V-
FIGURE 7. AUTOMATIC POWER-DOWN AND
INVALID TIMING DIAGRAMS
Receiver ENABLE Control
(ICL3221E, ICL3222E, ICL3223E, ICL3241E
Only)
Several devices also feature an EN input to control the
receiver outputs. Driving EN high disables all the
inverting (standard) receiver outputs placing them in a
high impedance state. This is useful to eliminate supply
current, due to a receiver output forward biasing the
protection diode, when driving the input of a powered
down (V_CC = GND) peripheral (see Figure 2). The enable
input has no effect on transmitter nor monitor (R_OUTB)
outputs.
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. 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-.
TABLE 3. REQUIRED CAPACITOR VALUES
V_CC
(V)
3.0 to 3.6
C₁
(µF)
0.1
C₂, C₃, C₄
(µF)
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 interoperability with
RS-232 devices.
Transmitter Outputs when
Exiting Power-Down
Figure 8 shows the response of two transmitter outputs
when exiting power-down 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
T1
2V/DIV
T2
V_CC = +3.3V
C1 - C4 = 0.1µF
TIME (20µs/DIV)
FIGURE 8. TRANSMITTER OUTPUTS WHEN EXITING
POWER-DOWN
Mouse Driveability
The ICL3241E and ICL3243E have been specifically
designed to power a serial mouse while operating from
low voltage supplies. Figure 9 shows the transmitter
18
FN4910.21
February 22, 2010