ICL3221E INTERSIL [Intersil Corporation], ICL3221E Datasheet - Page 14

• Manufacturer Part Number: ICL3221E
• Manufacturer: INTERSIL [Intersil Corporation]

Automatic powerdown operates when the FORCEON input
is low, and the FORCEOFF input is high. Tying FORCEON
high disables automatic powerdown, but manual powerdown
is always available via the overriding FORCEOFF input.
Table 2 summarizes the automatic powerdown functionality.
Devices with the automatic powerdown 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
powerdown, or forced on), so it is also useful for systems
employing manual powerdown circuitry. When automatic
powerdown is utilized, INVALID = 0 indicates that the
ICL32xxE is in powerdown mode.
The time to recover from automatic powerdown mode is
typically 100µs.
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
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS
TRANSMITTER
FIGURE 7. AUTOMATIC POWERDOWN AND INVALID
-0.3V
-2.7V
OUTPUT
INVALID
2.7V
0.3V
RECEIVER
OUTPUTS
INPUTS
V
V
INVALID LEVEL - POWERDOWN OCCURS AFTER 30µs
VALID RS-232 LEVEL - ICL32xxE IS ACTIVE
VALID RS-232 LEVEL - ICL32xxE IS ACTIVE
CC
INDETERMINATE - POWERDOWN MAY OR
INDETERMINATE - POWERDOWN MAY OR
CC
V+
V-
0
TIMING DIAGRAMS
0
AUTOPWDN
ICL3221E, ICL3222E, ICL3223E, ICL3232E, ICL3241E, ICL3243E
t
INVL
MAY NOT OCCUR
MAY NOT OCCUR
14
t
INVH
PWR UP
}
INVALID
REGION
(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
peripheral (see Figure 2). The enable input has no effect on
transmitter nor monitor (R
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-.
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.
Operation Down to 2.7V
ICL32xxE transmitter outputs meet RS-562 levels (
full data rate, with V
typically ensure interoperability with RS-232 devices.
Transmitter Outputs when Exiting
Powerdown
Figure 8 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.
3.0 to 3.6
4.5 to 5.5
3.0 to 5.5
V
TABLE 3. REQUIRED CAPACITOR VALUES
(V)
CC
1
without also increasing C
CC
as low as 2.7V. RS-562 levels
OUTB
0.047
1
(µF)
0.1
0.1
C
to the other capacitors).
1
1
2
) outputs.
’s value, however, do not
CC
, C
3
to ground with a
, and C
2
, C
3
, and C
4
CC
C
can be
2
, C
0.33
0.47
(µF)
= GND)
0.1
3
4
±
June 22, 2007
, C
3.7V), at
to
FN4910.19
4
1
.