TDA8757 datasheet(18/37 Pages) PHILIPS

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Philips Semiconductors

TDA8757

Triple 8-bit ADC 170 Msps

Preliminary data

Rev. 07 — 28 February 2002

18 of 37

9397 750 09457

The default programmed value is:

• Programmed code = 127

• Clamp code = 0

• ADC output = 0.

9.1.3

Coarse and Fine registers

These two registers enable the gain control: the AGC gain with the coarse register,

and the reference voltage with the ﬁne register. The coarse register programming

equation is as follows:

(3)

Where: Vref = 2.5 V.

The gain correspondence is given in Table 6. The gain is linear with reference to the

programming code (NFINE = 0).

The default programmed value is as follows:

• NCOARSE =32

• Gain = 0.825

• Vi to be full-scale = 1.212.

Table 5:

Coding

Programmed code

Clamp code

ADC output

−63.5

underﬂow

−63

−62.5

...

127

...

254

63.5

63 or 64

255

256

120

...

287

136

Table 6:

Typical gain correspondence (COARSE)

NCOARSE

Gain

Vi to be full-scale (V)

0.825

1.212

2.5

0.4

GAIN

COARSE

ref

FINE

------------------

–





⋅

------------------------------------------------







------

COARSE

ref . 512

FINE

–

()

------------------------------------------------





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