Semtech 2006
www.semtech.com
16-18
XE8805/05A
The equivalent LSB size at the input of the PGA chain is:
1
2
1
+
=
OSR
GD
V
LSB
TOT
REF
n
(V)
(Eq. 19)
Notice that the input voltage VIN,ADC of the ADC must satisfy the condition:
1
)
(
2
1
,
+
≤
OSR
V
REFN
REFP
ADC
IN
(V)
(Eq. 20)
to remain within the ADC input range.
16.7.8
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 IB_AMP_PGA[1:0] and IB_AMP_ADC[1:0] (see Table 16-26). 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.
IB_AMP_ADC
[1:0]
IB_AMP_PGA
[1:0]
ADC
Bias
Current
PGA
Bias
Current
Max. fS
[kHz]
00
01
10
11
x
1/4
I
ADC
1/2
I
ADC
3/4
I
ADC
IADC
x
62.5
125
250
500
x
00
01
10
11
x
1/4
I
PGA
1/2
I
PGA
3/4
I
PGA
IPGA
62.5
125
250
500
Table 16-26. ADC & PGA power saving modes and maximum sampling frequency
16.8
Specifications and Measured Curves
This section presents measurement results for the acquisition chain. A summary table with circuit specifications
and measured curves are given.
Not
Recommended
for
New
Designs