BTM510/511 Multimedia Module

Datasheet

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Figure 3: Single and Double Ended Line Inputs

A 15nH / 15pF low pass filter must be added to each input line and placed as close to the BTM511 input pins as

possible. Otherwise the BT envelope may be demodulated, causing audio artifacts in the 800 – 1600kHz range

that cannot be removed.

If using single-ended line input, it is only necessary to fit one low pass filter per channel. For both Stereo Line In

and Microphone modes, you may connect the input signal to either the positive or negative side of the input.

The unused input should be connected to either MIC_BIAS or AGND (Note: The ADK-BTM511-v04 design fits one

low pass filter on each of the 4 channel inputs).

The Left channel (MIC_AP_C / MIC_AN_C) should be used as the standard mono channel, the Right channel

inputs (MIC_BP_C / MIC_BN_C) can be used as an auxiliary mono channel or connected to AGND if unused

(Remember to fit the low pass filter on one or both of the unused Right channel inputs).

A typical line input signal has a voltage of 1.75Vrms or 5Vpk-pk. However, the BTM511 can only tolerate 0.4Vrms

on the audio inputs. A resistive network can be used to divide the input signal down to 0.4Vrms if necessary.

The audio inputs can operate in either line input mode or microphone mode. The input circuit has a two stage

amplifier – the first stage provides a fixed 24 dB gain and the second a variable gain of between -3 dB and 18 dB.

If an input gain of less than 24 dB is selected, then the first stage is switched out and the module is operating in

line input mode.

When operating in microphone mode the microphone should be biased as shown in Figure 4.

Figure 4: Microphone biasing for microphone mode