ICL3245ECAZ-T Datasheet, PDF (11/20 Pages) Intersil Corporation – ±15kV ESD Protected, +3V to +5.5V, 1Microamp, 1Mbps, RS-232 Transceivers

ICL3225E, ICL3227E, ICL3245E
(set), keeping the ICL32XXE powered down until FORCEON
transitions high, or until a transition occurs on a receiver or
transmitter input.
The INVALID output signal switches low to indicate that
invalid levels have persisted on all of the receiver inputs for
more than 30µs (see Figure 8), but this has no direct effect
on the state of the ICL32XXE (see the next sections for
methods of utilizing INVALID to power down the device).
INVALID switches high 1µs after detecting a valid RS-232
level on a receiver input. INVALID operates in all modes
(forced or automatic powerdown, or forced on), so it is also
useful for systems employing manual powerdown circuitry.
The time to recover from automatic powerdown mode is
typically 100µs.
Emulating Standard Automatic Powerdown
If enhanced automatic powerdown isn’t desired, the user can
implement the standard automatic powerdown feature (mimics
the function on the ICL3221E/ICL3223E/ICL3243E) by
connecting the INVALID output to the FORCEON and
FORCEOFF inputs, as shown in Figure 9. After 30µs of invalid
receiver levels, INVALID switches low and drives the
ICL32XXE into a forced powerdown condition. INVALID
switches high as soon as a receiver input senses a valid RS-
232 level, forcing the ICL32XXE to power on. See the “INVALID
DRIVING FORCEON AND FORCEOFF” section of Table 2 for
an operational summary. This operational mode is perfect for
handheld devices that communicate with another computer via
a detachable cable. Detaching the cable allows the internal
receiver pull-down resistors to pull the inputs to GND (an invalid
RS-232 level), causing the 30µs timer to time-out and drive the
IC into powerdown. Reconnecting the cablerestores valid
levels, causing the IC to power back up.
FORCEON
INVALID
FORCEOFF
ICL32XXE
CPU
I/O
UART
FIGURE 8. CONNECTIONS FOR AUTOMATIC POWERDOWN
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
Hybrid Automatic Powerdown Options
For devices which communicate only through a detachable
cable, connecting INVALID to FORCEOFF (with FORCEON
= 0) may be a desirable configuration. While the cable is
attached INVALID and FORCEOFF remain high, so the
enhanced automatic powerdown logic powers down the RS-
232 device whenever there is 30 seconds of inactivity on the
receiver and transmitter inputs. Detaching the cable allows
the receiver inputs to drop to an invalid level (GND), so
INVALID switches low and forces the RS-232 device to
power down. The ICL32XXE remains powered down until
the cable is reconnected (INVALID = FORCEOFF = 1) and a
transition occurs on a receiver or transmitter input (see
Figure 7). For immediate power up when the cable is
reattached, connect FORCEON to FORCEOFF through a
network similar to that shown in Figure 5.
RECEIVER
INPUTS
TRANSMITTER
INPUTS
TRANSMITTER
OUTPUTS
INVALID
OUTPUT
t_INVL
READY
OUTPUT
V+
t_INVH
t_AUTOPWDN
t_WU
t_AUTOPWDN
t_WU
V_CC
0
V-
FIGURE 9. ENHANCED AUTOMATIC POWERDOWN, INVALID AND READY TIMING DIAGRAMS
INVALID
} _REGION
11
FN4900.9
February 27, 2006