ICL3243EIA Datasheet, PDF (17/33 Pages) Intersil Corporation – ±15kV ESD Protected, +3V to +5.5V, 1μA, 250kbps, RS-232 Transmitters/Receivers

ICL3221E, ICL3222E, ICL3223E, ICL3232E, ICL3241E, ICL3243E
V_CC
TRANSITION
DETECTOR
TO
WAKE-UP
LOGIC
V_CC
R_X
POWERED
DOWN
UART
T_X
R2_OUTB
V_OUT = HI-Z
R2_OUT
T1_IN
ICL324XE
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
ICL3221E,
ICL3223E,
ICL3243E
CPU
I/O
UART
FIGURE 4. CONNECTIONS FOR MANUAL
POWER-DOWN WHEN NO VALID
RECEIVER SIGNALS ARE PRESENT
With any of the control schemes, the time required to
exit power-down, and resume transmission is only
100µs. A mouse, or other application, may need more
time to wake up from shutdown. If automatic
power-down is being utilized, the RS-232 device will
reenter power-down 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 power-down 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 POWER-DOWN LINE
0.1µF
1MΩ
FORCEOFF FORCEON
ICL3221E, ICL3223E, ICL3243E
FIGURE 5. CIRCUIT TO PREVENT AUTO
POWER-DOWN FOR 100ms AFTER
FORCED POWER-UP
Automatic Power-Down
(ICL3221E, ICL3223E, ICL3243E Only)
Even greater power savings is available by using the
devices which feature an automatic power-down
function. When no valid RS-232 voltages (see Figure 6)
are sensed on any receiver input for 30µs, the charge
pump and transmitters power-down, 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 power-down feature provides
additional system power savings without changes to the
existing operating system.
2.7V
VALID RS-232 LEVEL - ICL32xxE IS ACTIVE
INDETERMINATE - POWER-DOWN MAY OR
MAY NOT OCCUR
0.3V
-0.3V
INVALID LEVEL - POWER-DOWN OCCURS AFTER 30µs
INDETERMINATE - POWER-DOWN MAY OR
MAY NOT OCCUR
-2.7V
VALID RS-232 LEVEL - ICL32xxE IS ACTIVE
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER
LEVELS
Automatic power-down operates when the FORCEON
input is low, and the FORCEOFF input is high. Tying
FORCEON high disables automatic power-down, but
manual power-down is always available via the
overriding FORCEOFF input. Table 2 summarizes the
automatic power-down functionality.
17
FN4910.21
February 22, 2010