TAS5504 datasheet(21/96 Pages) TI

21 / 96 page

Introduction

SLES123 − October 2004

TAS5504

The decimal value of a 5.23 format number can be found by following the weighting shown in Figure 1−6. 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 1−6 applied to obtain the

magnitude of the negative number.

(1 or 0) x 23 + (1 or 0) x 22 + … + (1 or 0) x 20 + (1 or 0) x 2−1 + … + (1 or 0) x 2−4 + … + (1 or 0) x 2−23

23 Bit

22 Bit

20 Bit

2−1 Bit

2−4 Bit

2−23 Bit

Figure 1−6. Conversion Weighting Factors—5.23 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 1−7.

Coefficient

Digit 8

u u u

S x x x

Coefficient

Digit 7

x. x x x

Coefficient

Digit 6

x x x x

Coefficient

Digit 5

x x x x

Coefficient

Digit 4

x x x x

Coefficient

Digit 3

x x x x

Coefficient

Digit 2

x x x x

Coefficient

Digit 1

Fraction

Digit 5

Sign

Bit

Fraction

Digit 6

Fraction

Digit 4

Fraction

Digit 3

Fraction

Digit 2

Fraction

Digit 1

Integer

Digit 1

u = unused or don’t care bits

Digit = hexadecimal digit

Figure 1−7. Alignment of 5.23 Coefficient in 32-Bit I2C Word

As Figure 1−7 shows, the hex value of the integer part of the gain coefficient cannot be concatenated with the

hex value of the fractional part of the gain coefficient to form the 32-bit I2C coefficient. The reason is that the

28-bit coefficient contains 5 bits of integer, and thus the integer part of the coefficient occupies all of one hex

digit and the most significant bit of the second hex digit. In the same way, the fractional part occupies the lower

3 bits of the second hex digit, and then occupies the other five hex digits (with the eighth digit being the

zero-valued most significant hex digit).

1.4.2.2

48-Bit 25.23 Number Format

All level adjustment and threshold coefficients are 48-bit coefficients using a 25.23 number format. Numbers

formatted as 25.23 numbers means that there are 25 bits to the left of the decimal point and 23 bits to the right

of the decimal point. This is shown in Figure 1−8.

TAS5504 Datasheet(PDF) 21 Page - Texas Instruments

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