MCP2030A-I Datasheet, PDF (33/66 Pages) Microchip Technology – Three-Channel Analog Front-End Device

5.14.2 INACTIVITY TIMER
The Inactivity Timer is used to automatically return the
device to Standby mode, if there is no input signal. The
time-out period is approximately 16 ms (T_INACT), based
on the 32 kHz internal clock.
The purpose of the Inactivity Timer is to minimize
current draw by automatically returning to the lower
current Standby mode, if there is no input signal for
approximately 16 ms.
The timer is reset when:
• An amplitude change in LF input signal, either
high-to-low or low-to-high
• CS pin is low (any SPI command)
• Timer-related Soft Reset
The timer starts after AGC initialization time (T_AGC).
The timer causes a Soft Reset when:
• A previously received input signal does not
change either high-to-low or low-to-high for
T_INACT
The Soft Reset returns the device to Standby mode
where most of the analog circuits, such as the AGC,
demodulator and RC oscillator, are powered down. This
returns the device to the lower Standby Current mode.
5.14.3 ALARM TIMER
The Alarm Timer is used to notify the external MCU that
the device is receiving an input signal that does not pass
the output enable filter requirement. The time-out period
is approximately 32 ms (T_ALARM) in the presence of
continuing noise.
The Alarm Timer time-out occurs if there is an input
signal for longer than 32 ms that does not meet the
output enable filter requirements. The Alarm Timer
time-out causes:
a) The ALERT pin to go low.
b) The ALARM bit to set in the Status
STATUS Register 7 (Register 5-8).
The external MCU is informed of the Alarm timer time-
out by monitoring the ALERT pin. If the Alarm timer
time-out occurs, the external MCU can take
appropriate actions such as lowering channel
sensitivity or disabling channels. If the noise source is
ignored, the device can return to a lower standby
current draw state.
MCP2030
The timer is reset when the:
• CS pin is low (any SPI command).
• Output enable filter is disabled.
• LFDATA pin is enabled (signal passed output
enable filter).
The timer starts after the AGC initialization time.
The timer causes a low output on the ALERT pin when:
• Output enable filter is enabled and modulated
input signal is present for T_ALARM, but does not
pass the output enable filter requirement.
Note: The Alarm timer is disabled if the output
enable filter is disabled.
5.14.4 PULSE WIDTH TIMER
The Pulse Width Timer is used to verify that the
received output enable sequence meets both the
minimum T_OEH and minimum T_OEL requirements.
5.14.5 PERIOD TIMER
The Period Timer is used to verify that the received
output enable sequence meets the maximum T_OET
requirement.
5.14.6 AGC INITIALIZATION TIMER (T_AGC)
This timer is used to keep the output enable filter in
Reset while the AGC settles on the input signal. The
time-out period is approximately 3.5 ms. At the end of
this time (T_AGC), the input should remain high (T_PAGC),
otherwise the counting is aborted and a Soft Reset is
issued. See Figure 5-4 for details.
Note 1: The device needs continuous and
uninterrupted high input signal during
AGC initialization time (T_AGC). Any
absence of signal during this time may
reset the timer and a new input signal is
needed for AGC settling time, or may
result in improper AGC gain settings
which will produce invalid output.
2: The rest of the device section wakes up
if any of these input channels receive
the AGC settling time correctly. STATUS
Register 7 bits <4:2> (Register 5-8) indi-
cate which input channels have waken
up the device first. Valid input signal on
multiple input pins can cause more than
one channel's indicator bit to be set.
© 2005 Microchip Technology Inc.
DS21981A-page 33