ICL3221 INTERSIL [Intersil Corporation], ICL3221 Datasheet - Page 13

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

FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
POWERED
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN
DOWN
UART
POWERED
CPU
DOWN
V
UART
WAKE-UP
GND
CC
LOGIC
LOGIC
PWR
MGT
V
TO
CC
R
T
PERIPHERAL
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
X
FORCEOFF = GND
OR SHDN = GND, EN = V
X
TRANSITION
DETECTOR
Rx
Tx
V
CC
V
UART
SHDN = GND
OUT
I/O
R2
V
R2
OUT
= HI-Z
V
3-13
OUTB
FORCEOFF
FORCEON
INVALID
T1
CC
OUT
= V
IN
CC
CC
ICL3221/23/43
ICL324X
RS-232 CHIP
OLD
V
CURRENT
FLOW
CC
ICL3221 thru ICL3243
R2
T1
OUT
IN
With any of the above control schemes, the time required to
exit powerdown, and resume transmission is only 100 s. 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 30 s 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.
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 30 s, the charge pump and transmitters
powerdown, thereby reducing supply current to 1 A. 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.
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.
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS
FIGURE 5. CIRCUIT TO PREVENT AUTO POWERDOWN FOR
-0.3V
-2.7V
2.7V
0.3V
MANAGEMENT
POWER
UNIT
INVALID LEVEL - POWERDOWN OCCURS AFTER 30 s
VALID RS-232 LEVEL - ICL32XX IS ACTIVE
VALID RS-232 LEVEL - ICL32XX IS ACTIVE
INDETERMINATE - POWERDOWN MAY OR
INDETERMINATE - POWERDOWN MAY OR
100ms AFTER FORCED POWERUP
MASTER POWERDOWN LINE
MAY NOT OCCUR
MAY NOT OCCUR
FORCEOFF
ICL3221/23/43
0.1 F
FORCEON
1M