ICL3221E INTERSIL [Intersil Corporation], ICL3221E Datasheet - Page 13

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

The INVALID output always indicates whether or not a valid
RS-232 signal is present at any of the receiver inputs (see
Table 2), giving the user an easy way to determine when the
interface block should power down. In the case of a
disconnected interface cable where all the receiver inputs
are floating (but pulled to GND by the internal receiver pull
down resistors), the INVALID logic detects the invalid levels
and drives the output low. The power management logic
then uses this indicator to power down the interface block.
Reconnecting the cable restores valid levels at the receiver
inputs, INVALID switches high, and the power management
logic wakes up the interface block. INVALID can also be
used to indicate the DTR or RING INDICATOR signal, as
long as the other receiver inputs are floating, or driven to
GND (as in the case of a powered down driver). Connecting
FORCEOFF and FORCEON together disables the
automatic powerdown feature, enabling them to function as
a manual SHUTDOWN input (see Figure 4).
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
POWERED
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
DOWN
UART
POWERED
DOWN
V
UART
WAKE-UP
GND
CC
LOGIC
V
TO
CC
R
T
PERIPHERAL
X
X
FORCEOFF = GND
OR SHDN = GND, EN = V
TRANSITION
DETECTOR
Rx
Tx
ICL3221E, ICL3222E, ICL3223E, ICL3232E, ICL3241E, ICL3243E
V
CC
V
SHDN = GND
OUT
R2
V
R2
OUT
= HI-Z
V
OUTB
T1
CC
OUT
13
= V
IN
CC
CC
ICL324XE
RS-232 CHIP
OLD
V
CURRENT
FLOW
CC
R2
T1
OUT
IN
With any of the above control schemes, the time required to
exit powerdown, and resume transmission is only 100µs. A
mouse, or other application, 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 ICL32xxE powering
up. Figure 5 illustrates a circuit that keeps the ICL32xxE
from initiating automatic powerdown for 100ms after
powering up. This gives the slow-to-wake peripheral circuit
time to reestablish valid RS-232 output levels.
Automatic Powerdown
(ICL3221E, ICL3223E, ICL3243E Only)
Even greater power savings is available by using the
devices which feature an 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
1µA. 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 ICL32xxE
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.
FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN
FIGURE 5. CIRCUIT TO PREVENT AUTO POWERDOWN FOR
MANAGEMENT
POWER
CPU
UNIT
LOGIC
PWR
MGT
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
100ms AFTER FORCED POWERUP
UART
MASTER POWERDOWN LINE
I/O
ICL3221E, ICL3223E, ICL3243E
FORCEOFF
FORCEON
INVALID
FORCEOFF
0.1µF
FORCEON
ICL3221E,
ICL3223E,
ICL3243E
1MΩ
June 22, 2007
FN4910.19