ICL3221 INTERSIL [Intersil Corporation], ICL3221 Datasheet - Page 14

• Manufacturer Part Number: ICL3221
• Description: 1 Microamp Supply-Current, +3V to +5.5V, 250kbps, RS-232 Transmitters/Receivers
• Manufacturer: INTERSIL [Intersil Corporation]

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 30 s (see Figure 7). INVALID switches high 1 s
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
ICL32XX is in powerdown mode.
The time to recover from automatic powerdown mode is
typically 100 s.
Receiver ENABLE Control (ICL3221/22/23/41 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
peripheral (see Figure 2). The enable input has no effect on
transmitter nor monitor (R
Capacitor Selection
The charge pumps require 0.1 F 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)
TRANSMITTER
FIGURE 7. AUTOMATIC POWERDOWN AND INVALID TIMING
OUTPUT
INVALID
RECEIVER
OUTPUTS
INPUTS
1
V
V
CC
CC
V+
without also increasing C
V-
0
DIAGRAMS
0
AUTOPWDN
t
INVL
OUTB
3-14
1
to the other capacitors).
1
2
) outputs.
’s value, however, do not
, C
3
, and C
2
, C
t
INVH
3
, and C
4
CC
can be
= GND)
ICL3221 thru ICL3243
PWR UP
4
}
to
INVALID
REGION
usually rises at low temperatures and it influences the
amount of ripple on V+ and V-.
Power Supply Decoupling
In most circumstances a 0.1 F 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 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 3k in parallel with 2500pF. Note
that the transmitters enable only when the magnitude of the
supplies exceed approximately 3V.
Mouse Driveability
The ICL324X have been specifically designed to power a
serial mouse while operating from low voltage supplies.
Figure 9 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). The Automatic Powerdown feature
does not work with a mouse, so FORCEOFF and
FORCEON should be connected to V
5V/DIV
2V/DIV
FIGURE 8. TRANSMITTER OUTPUTS WHEN EXITING
3.0 to 3.6
4.5 to 5.5
3.0 to 5.5
V
V
C1 - C4 = 0.1 F
TABLE 3. REQUIRED CAPACITOR VALUES
(V)
CC
CC
= +3.3V
POWERDOWN
FORCEOFF
TIME (20 s/DIV.)
0.047
( F)
0.1
0.1
C
1
CC
to ground with a
CC
.
C
2
, C
0.33
0.47
( F)
0.1
3
T1
T2
, C
4
1
.