MCP2035 datasheet(34/68 Pages) MICROCHIP

34 / 68 page

MCP2035

DS22304A-page 34

 2012 Microchip Technology Inc.

5.8

Carrier Clock Detector

The Carrier Clock Detector senses the input carrier

cycles. The output of the detector switches digitally at

the signal carrier frequency. Carrier clock output is

available when the output is selected by the DATOUT

bit in Configuration Register 1 (Register 5-2).

5.9

Demodulator

The Demodulator consists of a full-wave rectifier, low-

pass filter, peak detector and Data Slicer that detects

the envelope of the input signal.

5.10

Data Slicer

The Data Slicer consists of a reference generator and

comparator. The Data Slicer compares the input with

the reference voltage. The reference voltage comes

from the minimum modulation depth requirement

setting and input peak voltage.

5.11

Output Enable Filter

The Output Enable Filter enables the LFDATA output

once the incoming signal meets the wake-up sequence

requirements

(see

Section 5.14

“Configurable

Output Enable Filter”

5.12

Received Signal Strength

Indicator (RSSI)

The RSSI provides a current which is proportional to

the input signal amplitude (see Section 5.29.3

“Received

Signal

Strength

Indicator

(RSSI)

Output”

5.13

Analog Front-End Timers

The device has an internal 32 kHz RC oscillator. The

oscillator is used in several timers:

• Inactivity Timer

•Alarm Timer

• Pulse Width Timer

• Period Timer

• AGC Settling Timer

5.13.1

RC OSCILLATOR

The RC oscillator generates a 32 kHz internal clock.

5.13.2

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 (TINACT), 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 the 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 (TAGC).

The timer causes a Soft Reset when:

• A previously received input signal does not

change either high-to-low or low-to-high for

TINACT

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.

5.13.3

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 (TALARM) 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 the input channel. If the noise

source is ignored, the device can return to a lower

standby current draw state.

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 TALARM, but does not

pass the output enable filter requirement.

Note:

The Alarm Timer is disabled if the output

enable filter is disabled.

MCP2035 Datasheet(PDF) 34 Page - Microchip Technology

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