TDA5235
Functional Description
2.6.2.3 Fast Fall Back to SLEEP (FFB)
This mode is used to switch off the receiver, if there is no RF signal, as quickly as
possible to reduce power consumption.
During the search for wake-up data, there is a check for a bit stream, to which the system
can be synchronized. If there is no synchronization to a bit stream within the so-called
Sync Search Time Out (SYSRCTO), the wake-up search for this channel is stopped. If
synchronization to a bit stream is possible (and not lost again), the TDA5235 waits if the
wake-up criterion is fulfilled. If the wake-up criterion is not fulfilled (in worst case, if the
last bit of an expected wake-up data pattern is wrong), the wake-up procedure for this
configuration is stopped, and the TDA5235 tries to synchronize on the next
configuration, or falls back to sleep. That means that the effective search time and,
consequently, the receiver active time is significantly shorter, and power consumption is
reduced, when no input signal is present. Calculation of Sync Search Time Out can be
found in Chapter 2.4.8.8 RUNIN, Synchronization Search Time and Inter-Frame
Time.
The needed time for detecting that no relevant transmission took place can be further
reduced by using Ultrafast Fall Back to SLEEP (UFFB). When there was no Wake-up on
Level criterion fulfilled in UFFB Mode during the Observation Time (TWULOT, see
Chapter 2.4.8.5), then the system goes back to SLEEP (or to next config). This can
further reduce the receiver active time, when no data is available. When Wake-up on
Level criterion was fulfilled, then the system proceeds with normal FFB functionality
(SYSRCTO, optional Wake-up data criterion).
Note: UFFB and FFB start working at the same time!
Ultrafast Fall Back to SLEEP is working, when a Wake-up on Data criterion is selected,
the UFFBLCOO bit is enabled and FFB or PWUS mode is selected. The UFFB level
criterion can be selected in the x_WUC register.
RF signal
e.g. ASK
t
RX ON
SLEEP
UFFB
FFB
FFB
t
tWULOT
tStartup
tSYSRCTO
tWU-data-pattern
tON
Figure 82
Ultrafast Fall Back to SLEEP
Data Sheet
117
V1.0, 2010-02-19
INFINEON [ Infineon ]
