Verdin Development Board Errata
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Errata #6:
HAR-7206 – Series capacitor values are too small for the audio codec's
speaker output to be used in a stereo setup
Affected Version:
Verdin Development Board V1.1A
Fixed in:
To be scheduled
6.1
Customer Impact
The audio output is significantly attenuated or not audible at all when the audio codec's speaker
output is used in combination with external speakers connected in a stereo setup.
The issue does not affect the speaker output when the external speakers are connected in a mono
setup.
6.2
Description
The audio codec featured on the Verdin Development Board V1.1 includes an integrated speaker
driver.
The Verdin Development Board V1.1 provides two audio codec speaker output operating modes:
mono and stereo. In a mono setup, one or two external speakers are connected as a Bridge Tied
Load (BTL) to the connectors X28 or X29. In this setup, the speaker output should work fine.
In a stereo setup, two external speakers are connected to the connector X13. In this case, one end
of each speaker's coil is connected to the common ground pin (GND), the other ends are
connected to the audio codec IC through the capacitors C182 or C183, respectively.
The capacitors C182 (1uF) and C183 (1uF), in conjunction with the speaker's impedance (8Ohm),
form high-pass filters. The cut-off frequency of the high-pass filters is around 20 kHz.
𝑓 =
1
2𝜋𝑅𝐶
=
1
2𝜋 ∗ 8𝑂ℎ𝑚 ∗ 1𝑢𝐹
≈ 20𝑘𝐻𝑧
This frequency is at the upper edge of the audible frequency range, and lower frequencies are
attenuated/filtered out by the aforementioned high-pass filter.
6.3
Workaround
A partial workaround has already been applied to the Verdin Development Board V1.1A: 0Ohm
resistors have assembled instead of the capacitors C182 and C183. To complete the workaround,
external capacitors connected in series with the external speakers are required (see Figure 3).
The exact values of the capacitors depend on the desired cut-off frequency and the impedance of
the speakers. Some applications may not require the complete audible frequency range of approx.
20Hz
–
20Hz to be available. The low-frequency limit is 100Hz for many low-power speakers, so
going below this cut-off frequency may be unnecessary.
For 8Ohm speakers, we recommend using either 220uF series capacitors for a cut-off frequency of
approximately 90Hz or 470uF for 42Hz respectively (minimum 6.3V rated in both cases).
