SX8724C Datasheet, PDF (33/67 Pages) Semtech Corporation – ZoomingADC for sensing data acquisition

SX8724C
ZoomingADC for sensing data acquisition
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
In "continuous-time" mode, the input signal is repeatedly converted into digital. After a conversion is finished, a new
one is automatically initiated. The new value is then written in the result register, and the corresponding internal
trigger pulse is generated. This operation is sketched in Figure 17. The conversion time in this case is defined as TCONV_.
Internal trig
Tconv
Output code RegACOut[15:0]
Busy
Ready
1/fs
Figure 17. ADC “Continuous-Time” Operation
In the "on-request" mode, the internal behavior of the converter is the same as in the "continuous-time" mode, but the
conversion is initiated on user request (with the Start bit). As shown in Figure 18, the conversion time is also TCONV.
Internal trig
Tconv
START Request
Output code RegACOut[15:0]
Busy
Ready
Figure 18. ADC “On-Request” Operation
7.7.8 Output Code Format
The ADC output code is a 16-bit word in two's complement format (see Table 19). For input voltages outside the range,
the output code is saturated to the closest full-scale value (i.e. 0x7FFF or 0x8000). For resolutions smaller than 16 bits,
the non-significant bits are forced to the values shown in Table 20. The output code, expressed in LSBs, corresponds to:
OUT _ADC
= 2¹⁶ ⋅ ^{V IN , ADC}
V _REF
⋅ ^{OSR + 1}
OSR
Equation 18
Recalling Equation 10, page 25, this can be rewritten as:
OUT_ADC
=
2¹⁶
⋅ ^VIN
V_REF
⋅ _{⎜⎜⎝⎛}GD_TOT
− GDoff_TOT
⋅ S ⋅ ^VREF
V_IN
⎟⎟⎠⎞
⋅
OSR +1
OSR
[LSB]
Equation 19
Revision 1.01
© Semtech
January 2011
Page 33
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