PCM1861 datasheet(37/115 Pages) TI

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Time of loss of signal (Y minutes)

INT

Threshold

Level

1 msec

Stopped BCK and LRCK by the Host

Sleep State

PCM1861, PCM1863, PCM1865

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SLAS831C – MARCH 2014 – REVISED AUGUST 2014

ADCs (continued)

8.14.2.2 Energysense Description

Energysense functionality has been added to the PCM186x to aid with auto-sleep and auto-wakeup for audio

systems that are expected to be sold within the European Union. The latest EcoDesign legislation in Europe has

demanded that products consume less than 500 mW in standby. Most off-the-shelf external power adaptors can

consume 300mW when idling, leaving the system with only 200 mW available. In many systems that requires

that almost everything be powered down in sleep mode, to be powered back up when signal enterers the system

again.

Energysense is split into two functions: Signal Loss Flag and Signal Resume Flag. Both are available on the

PCM186x software controlled devices. The PCM1861 only supports signal resume. Usage is shown below. By

default, the Signal Resume Threshold is set at –57dBFS.

Table 15. Energysense States

MODE

PURPOSE

CONDITIONS

POSITIVE OUTCOME

WORST CASE

SLEEP

Detect Input Signal and Wake up

BCK and LRCK stopped (not locked) or

Host Wakes and services interrupt (reads

Host Doesn't respond or start clocks.

(Signal Detect

from SLEEP

Mode)

Trigger Interrupt when input crosses

Host Starts BCK/LRCK. (Moving system to

PCM186x keeps triggering interrupts until

above (threshold)

ACTIVE mode) or writes to register.

host responds.

Trigger for 1ms every X seconds until

clocks start (x=1 by default)

ACTIVE

Detect content below (threshold)

BCK and LRCK are currently running

System can choose to go to sleep or not. If

If system does not sleep, remain in Mode

(Signal Loss

over time

not, reset interrupt

2, and prompt every Y.

Mode)

Assist system to sleep after

If no content above -(threshold) dB for Y

If System decides to sleep, stop BCK/LRCK.

MCU will need to mask that interrupt.

audio inactivity (for example,

minutes, drive interrupt.

This will move PCM186x to SLEEP mode.

Source is off, but speaker still

on)

8.14.2.3 Energysense Signal Loss Flag

The main ADC constantly monitors the input signal level while in ACTIVE mode. Should the input level remain

below a register defined threshold (for example –60dB) for a register defined amount of time (for example 1

minute), an interrupt will be generated.

Should the system MCU decide to move to SLEEP mode, the PCM186x can be moved to SLEEP by stopping

BCK/LRCK or using a register. See Table 15 for detail. If BCK and LRCK are stopped by the Host after the

interrupt, the device goes to the sleep state as shown in Figure 31. Otherwise, the device repeats the interrupt

every Y minutes as shown in Figure 32. The interrupt can be cleared by reading the status register.

Figure 31. Energysense Signal Loss

In a typical application, the host MCU will note and reset this register multiple times until a system sleep number

is hit. For example, a 5-minute signal loss could be implemented by using the default 1-minute timeout on the

PCM186x, and counting 5 interrupts. An example can be seen in the diagram below.

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