ISL4223E INTERSIL [Intersil Corporation], ISL4223E Datasheet - Page 7

• Manufacturer Part Number: ISL4223E
• Description: QFN Packaged, +/-15kV ESD Protected, +2.7V to +5.5V, 150Nanoamp, 250kBps, RS-232 Transmitters/Receivers
• Manufacturer: INTERSIL [Intersil Corporation]

mode. For always enabled operation, FORCEON and
FORCEOFF are both strapped high. To switch between
active and powerdown modes, under logic or software
control, only the FORCEOFF input need be driven. The
FORCEON state isn’t critical, as FORCEOFF dominates
over FORCEON. Nevertheless, if strictly manual control over
powerdown is desired, the user must strap FORCEON high
to disable the automatic powerdown circuitry.
Connecting FORCEOFF and FORCEON together disables
the automatic powerdown feature, enabling them to function
as a manual SHUTDOWN input (see Figure 4).
The time to recover from automatic powerdown mode is
typically 100µs.
FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN
RECEIVER INPUT?
RS-232 SIGNAL
PRESENT AT
CPU
LOGIC
YES
YES
YES
YES
PWR
MGT
NO
NO
NO
NO
NO
NO
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
UART
I/O
FORCEOFF
FORCEOFF
FORCEON
INVALID
INPUT
H
H
H
H
H
H
7
L
L
L
L
TABLE 2. POWERDOWN AND ENABLE LOGIC TRUTH TABLE
FORCEON
INPUT
ISL422XE
H
H
L
L
L
L
X
X
X
X
INPUT
ISL4221E, ISL4223E
EN
H
H
H
H
H
L
L
L
L
L
TRANSMITTER
OUTPUTS
High-Z
High-Z
High-Z
High-Z
High-Z
High-Z
Active
Active
Active
Active
Automatic Powerdown
Even greater power savings is available by using the
automatic powerdown function. When no valid RS-232
voltages (see Figure 6) are sensed on any receiver input for
30µs, the charge pump and transmitters powerdown, thereby
reducing supply current to 10nA. Invalid receiver levels occur
whenever the driving peripheral’s outputs are shut off
(powered down) or when the RS-232 interface cable is
disconnected. The ISL422XE powers back up whenever it
detects a valid RS-232 voltage level on any receiver input.
This automatic powerdown feature provides additional
system power savings without changes to the existing
operating system.
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.
Some applications may need more time to wake up from
shutdown. If automatic powerdown is being utilized, the RS-
232 device will reenter powerdown if valid receiver levels
aren’t reestablished within 30µs of the ISL422XE powering
up. Figure 5 illustrates a circuit that keeps the ISL422XE
FIGURE 5. CIRCUIT TO PREVENT AUTO POWERDOWN FOR
RECEIVER
OUTPUTS
MANAGEMENT
High-Z
High-Z
High-Z
High-Z
High-Z
Active
Active
Active
Active
Active
POWER
UNIT
100ms AFTER FORCED POWERUP
OUTPUT
INVALID
H
H
H
H
L
L
L
L
L
L
MASTER POWERDOWN LINE
Normal Operation
(Auto Powerdown Disabled)
Normal Operation
(Auto Powerdown Enabled)
Powerdown Due to Auto Powerdown
Logic
Manual Powerdown
Manual Powerdown w/Rcvr. Disabled
Manual Powerdown
Manual Powerdown w/Rcvr. Disabled
FORCEOFF
MODE OF OPERATION
ISL422XE
0.1µF
FORCEON
1MΩ