MCP2035-ISLASHST datasheet(37/68 Pages) MICROCHIP

37 / 68 page

 2012 Microchip Technology Inc.

DS22304A-page 37

MCP2035

5.14

Configurable Output Enable Filter

The purpose of this filter is to enable the LFDATA

output and wake the external microcontroller only after

receiving a specific sequence of pulses on the LC input

pin. Therefore, it prevents waking up the external

microcontroller due to noise or unwanted input signals.

The circuit compares the timing of the demodulated

header waveform with a pre-defined value, and

enables the demodulated LFDATA output when a

match occurs.

The output enable filter consists of a high (TOEH) and

low duration (TOEL) of a pulse immediately after the

AGC settling gap time. The selection of high and low

times further implies a max period time. The output

enable high and low times are determined by SPI

programming. Figure 5-3 and Figure 5-4 show the

output enable filter waveforms.

There should be no missing cycles during TOEH.

Missing cycles may result in failing the output enable

condition.

FIGURE 5-3:

Output Enable Filter Timing.

FIGURE 5-4:

Output Enable Filter Timing Example (Detailed).

Data Packet

 TOEH

 TOEL

Required Output Enable Sequence

LFDATA output is enabled

on this rising edge

 TOET

Demodulator

Output

TGAP

Device Wake-up

Start bit

AGC

(TAGC + TPAGC)

TSTAB

and AGC Stabilization Gap Pulse

LF Coil Input

Demodulated LFDATA Output

Low

Standby

Mode

Current

Filter is passed and

LFDATA is enabled

Gap

TPAGC

3.5 ms

Filter

starts

TGAP

Start bit for data

(need

TSTAB

 TOEH

 TOEL

 TOET

 2TE

(AFE Stabilization)

“high”) Pulse

TAGC

(AGC initialization time)

Legend:

TAGC = AGC initialization time

TGAP = AGC stabilization gap

TPAGC = High time after TAGC

TOEH = Minimum output enable filter high time

TSTAB = AGC stabilization time (TAGC + TPAGC)TOEL = Minimum output enable filter low time

TE = Time element of pulse (minimum pulse width)

TOET = Maximum output enable filter period

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