SX8724C Datasheet, PDF (24/67 Pages) Semtech Corporation – ZoomingADC for sensing data acquisition

ADVANCED COMMUNICATIONS & SENSING
SX8724C
ZoomingADC for sensing data acquisition
DATASHEET
Table 13. PGA3 Gain and Offset Settings
Pga3Gain bitfield
(RegACCfg3[6:0])
...
1000000
...
1111111
PGA3 Gain
GD3 [V/V]
...
64/12
...
127/12 (=10.58)
Pga3Offset bitfield
(RegACCfg4[6:0])
1000001
1000010
...
1010000
...
1100000
...
1111111
PGA3 Offset
GDOFF3 [V/V]
-1/12 (=-0.083)
-2/12
...
-16/12
...
-32/12
...
-63/12 (=-5.25)
The output of PGA3 is also the input of the ADC. Thus, similarly to PGA2, we find that the voltage entering the ADC is
given by:
V_{IN ,ADC} = GD₃ ⋅V_D2 − GDoff₃ ⋅ S ⋅V_REF [V ]
Equation 7
where GD3 and GDOFF3 are respectively the gain and offset of PGA3 (in V/V). The control words are Pga3Gain[6:0] and
Pga3Offset[6:0].
To remain within the signal compliance of the PGA stages (no saturation), the condition:
V_IN , V_D1 , V_D2
< ^VBATT
2
Equation 8
must be verified.
To remain within the signal compliance of the ADC (no saturation), the condition:
must be verified.
V_{IN ,ADC}
< _⎜⎛ ^VREF
⎝²
⎟⎞⎜⎛ ^{OSR − 1}⎟⎞
⎠⎝ ^OSR ⎠
Equation 9
Revision 1.01
© Semtech
January 2011
Page 24
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