ICL3232CV-T Datasheet, PDF (12/28 Pages) Intersil Corporation – One Microamp Supply-Current, +3V to +5.5V, 250kbps, RS-232 Transmitters/Receivers

ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243
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).
V_CC
V_CC
V_CC
CURRENT
FLOW
POWERED
DOWN
UART
GND
V_OUT = V_CC
Rx
Tx
SHDN = GND
OLD
RS-232 CHIP
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
V_CC
TRANSITION
DETECTOR
TO
WAKE-UP
LOGIC
V_CC
R2_OUTB
R_X
POWERED
DOWN
UART
T_X
V_OUT = HI-Z
R2_OUT
T1_IN
ICL324X
FORCEOFF = GND
OR SHDN = GND, EN = V_CC
R2_IN
T1_OUT
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
PWR
MGT
LOGIC
FORCEOFF
FORCEON
INVALID
ICL3221/23/43
CPU
I/O
UART
FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
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 ICL32XX powering
up. Figure 5 illustrates a circuit that keeps the ICL32XX 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.
POWER
MANAGEMENT
UNIT
MASTER POWERDOWN LINE
0.1µF
1MΩ
FORCEOFF FORCEON
ICL3221/23/43
FIGURE 5. CIRCUIT TO PREVENT AUTO POWERDOWN FOR
100ms AFTER FORCED POWERUP
Automatic Powerdown (ICL3221/23/43 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 ICL32XX
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.
12
FN4805.21
March 1, 2006