TDA8757 Datasheet, PDF (18/37 Pages) NXP Semiconductors – Triple 8-bit ADC 170 Msps

Philips Semiconductors
TDA8757
Triple 8-bit ADC 170 Msps
Table 5: Coding
Programmed code
0
1
2
...
127
...
254
255
256
...
287
Clamp code
−63.5
−63
−62.5
...
0
...
63.5
64
120
...
136
ADC output
underflow
0
...
63 or 64
64
120
...
136
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:


GAIN
=




--------^N-----^C---^O----^A---^R---^S---^E----⁺-----¹---------
V _ref
⋅


1
–
3^--N--2^--F--×^--I-N--1^--E-6^{-}




×
1^--1--6^-
=


V^-----_r^--_e^--N_f^---.^-C(^---5^-O--1^-A--2^-R---S–^---E--N^--+---_F^--1-_I^--_N^---_E^----)
×
32
(3)
Where: V_ref = 2.5 V.
The gain correspondence is given in Table 6. The gain is linear with reference to the
programming code (N_FINE = 0).
Table 6: Typical gain correspondence (COARSE)
N_COARSE
Gain
32
0.825
99
2.5
V_i to be full-scale (V)
1.212
0.4
The default programmed value is as follows:
• N_COARSE = 32
• Gain = 0.825
• V_i to be full-scale = 1.212.
9397 750 09457
Preliminary data
Rev. 07 — 28 February 2002
© Koninklijke Philips Electronics N.V. 2002. All rights reserved.
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