TAS5715_14 Datasheet, PDF (39/75 Pages) Texas Instruments – 25-W DIGITAL AUDIO POWER AMPLIFIER WITH EQ AND DRC

TAS5715
www.ti.com
SLOS645 – AUGUST 2010
The decimal value of a 3.23 format number can be found by following the weighting shown in Figure 52. If the
most significant bit is logic 0, the number is a positive number, and the weighting shown yields the correct
number. If the most significant bit is a logic 1, then the number is a negative number. In this case every bit must
be inverted, a 1 added to the result, and then the weighting shown in Figure 53 applied to obtain the magnitude
of the negative number.
2¹ Bit
2⁰ Bit
2^–1 Bit
2^–4 Bit
2^–23 Bit
(1 or 0) ´ 2¹ + (1 or 0) ´ 2⁰ + (1 or 0) ´ 2^–1 + ....... (1 or 0) ´ 2^–4 + ....... (1 or 0) ´ 2^–23
M0126-01
Figure 53. Conversion Weighting Factors—3.23 Format to Floating Point
Gain coefficients, entered via the I²C bus, must be entered as 32-bit binary numbers. The format of the 32-bit
number (4-byte or 8-digit hexadecimal number) is shown in Figure 54
Sign
Bit
Fraction
Digit 6
Integer
Digit 1
Fraction
Digit 1
Fraction
Digit 2
Fraction
Digit 3
Fraction
Digit 4
Fraction
Digit 5
u u u u u u S x x. x x x x x x x x x x x x x x x x x x x x x x x 0
Coefficient
Digit 8
Coefficient
Digit 7
Coefficient
Digit 6
Coefficient
Digit 5
Coefficient
Digit 4
Coefficient
Digit 3
Coefficient
Digit 2
Coefficient
Digit 1
u = unused or don’t care bits
Digit = hexadecimal digit
Figure 54. Alignment of 3.23 Coefficient in 32-Bit I²C Word
M0127-01
Table 1. Sample Calculation for 3.23 Format
db
Linear
Decimal
Hex (3.23 Format)
0
1
8,388,608
80 0000
5
1.77
14,917,288
00E3 9EA8
–5
0.56
4,717,260
0047 FACC
X
L = 10^(X/20)
D = 8388608 × L H = dec2hex (D, 8)
Table 2. Sample Calculation for 9.17 Format
db
Linear
Decimal
Hex (9.17 Format)
0
1
131,072
20 000
5
1.77
231,997
38 A3D
–5
0.56
73,400
11 EB8
X
L = 10^(X/20)
D = 131,072 × L H = dec2hex (D, 8)
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