There are three common situations of pop sound when power on
(1) Vdd and en are connected and powered on. At this time, the pop tone caused by instability in the chip. At this time, it is recommended to add RC before en for delay, such as 10K, 1uF.
(2) Pop sound caused by en separate power on,
When the peripheral does not match the parameters of the power amplifier, the charging time of the input resistor and capacitor of the power amplifier is long, and the charging is not synchronized, resulting in a signal difference between the two inputs, which is amplified by the power amplifier and causes a pop sound. For example, the following figure shows the charging curve of RC. This pop tone is generally effective in reducing resistance and capacitance.
(3) Pop sound caused by previous sound source or software
Generally, the output of the previous sound source also has a bias voltage. If it is not handled properly, or the software timing is wrong after the system is turned on, it will also cause pop sound. At this time, it can be judged by turning on the power amplifier after en has been turned up. If EN has been turned up and there is pop sound, it is judged as the above situation. Grab the sound source and start-up sequence with an oscilloscope. It is suggested that after the previous chip outputs stably (the bias voltage is established stably), MCU will give en start-up signal.
The pop tone of shutdown can also be divided into several situations
The most common problem of shutdown pop tone is the problem of software timing
For example, when the prompt tone is played during shutdown, if the software immediately pulls down en and turns off the sound source at the same time, as shown in the following figure, because the general power amplifier will do a little shutdown delay, the main chip MCU will turn off the sound source when the power amplifier is not completely turned off, and the inconsistent discharge rate will cause the differential pressure to be amplified by the power amplifier, resulting in the shutdown pop tone.
In order to prevent shutdown pop sound, it is recommended to turn off the sound source after the software pulls down en and delays t2>50ms, as shown in the following figure.
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