STA559BWQS13TR STMICROELECTRONICS [STMicroelectronics], STA559BWQS13TR Datasheet - Page 56

• Manufacturer Part Number: STA559BWQS13TR
• Description: 5-V, 2-A, 2.1-channel high-efficiency digital audio system with QSound QHD
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Register description
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Coefficients stored in the user defined coefficient RAM are referenced in the following
manner:
where x represents the channel and the y the biquad number. For example C2H41 is the b
coefficient in the fourth biquad for channel 2.
Additionally, the STA559BWQS allows specification of a high-pass filter (processing
channels 1 and 2) and a lo-pass filter (processing channel 3) to be used for bass-
management crossover when the XO setting is 000 (user-defined). Both of these filters
when defined by the user (rather than using the preset crossover filters) are 2
that use the biquad equation noted above. They are loaded into the C12H0-4 and C3Hy0-4
areas of RAM noted in the table below.
By default, all user-defined filters are pass-thru where all coefficients are set to 0, except the
b
Pre-scale
The STA559BWQS provides a multiplication for each input channel for the purpose of
scaling the input prior to EQ. This pre-EQ scaling is accomplished by using a 24-bit signed
fractional multiplier, with 0x800000 = -1 and 0x7FFFFF = 0.9999998808. The scale factor
for this multiply is loaded into RAM using the same I
and the bass-management. All channels can use the channel 1 pre-scale factor by setting
the Biquad link bit. By default, all pre-scale factors are set to 0x7FFFFF.
Post-scale
The STA559BWQS provides one additional multiplication after the last interpolation stage
and the distortion compensation on each channel. This post-scaling is accomplished by
using a 24-bit signed fractional multiplier, with 0x800000 = -1 and 0x7FFFFF =
0.9999998808. The scale factor for this multiply is loaded into RAM using the same I
registers as the biquad coefficients and the bass-management. This post-scale factor can
be used in conjunction with an ADC equipped micro-controller to perform power-supply
error correction. All channels can use the channel 1 post-scale factor by setting the post-
scale link bit. By default, all post-scale factors are set to 0x7FFFFF. When Line output is
being utilized, channel 3 post-scale will affect both channels 3 and 4.
Over-current post-scale
The STA559BWQS provides a simple mechanism for reacting to over-current detection in
the power-block. When the ocwarn input is asserted, the over-current post-scale value is
used in place of the normal post-scale value to provide output attenuation on all channels.
The default setting provides 3 dB of output attenuation when ocwarn is asserted.
The amount of attenuation to be applied in this situation can be adjusted by modifying the
Over-current Post-scale value. As with the normal post-scale, this scaling value is a 24-bit
signed fractional multiplier, with 0x800000 = -1 and 0x7FFFFF = 0.9999998808. By default,
the over-current post-scale factor is set to 0x
applied, it remains until the device is reset.
0
/2 coefficient which is set to 0x400000 (representing 0.5)
CxHy0 = b
CxHy1 = b
CxHy2 = -a
CxHy3 = -a
CxHy4 = b
1
2
0
1
2
/2
/2
/2
5A9DF7
2
. Once the over-current attenuation is
C registers as the biquad coefficients
STA559BWQS
nd
order filters
2
C
2