SX8724C Datasheet, PDF (35/67 Pages) Semtech Corporation – ZoomingADC for sensing data acquisition

ADVANCED COMMUNICATIONS & SENSING
The equivalent LSB size at the input of the PGA chain is:
SX8724C
ZoomingADC for sensing data acquisition
DATASHEET
LSB = ¹ ⋅ ^VREF ⋅ ^OSR [V / V ]
2 ⁿ GD_TOT OSR + 1
Equation 22
Notice that the input voltage V_IN,ADC of the ADC must satisfy the condition:
V_{IN , ADC}
≤
1
2
⋅ (V_REFP
− V_REFN
) ⋅ ^OSR
OSR + 1
Equation 23
to remain within the ADC input range.
7.7.9 Power Saving Modes
During low-speed operation, the bias current in the PGAs and ADC can be programmed to save power using the
control words IbAmpPga[1:0] and IbAmpAdc[1:0] (see Table 21). If the system is idle, the PGAs and ADC can even be
disabled, thus, reducing power consumption to its minimum. This can considerably improve battery lifetime.
Table 21. ADC & PGA power saving modes and maximum sampling frequency
IbAmpAdc [1:0]
00
01
11
IbAmpPga [1:0] ADC Bias Current PGA Bias Current
1/4 x IADC
1/2 x IADC
IADC
00
1/4 x IPGA
01
1/2 x IPGA
11
IPGA
Max. fs [kHz]
125
250
500
125
250
500
Revision 1.01
© Semtech
January 2011
Page 35
www.semtech.com/products/