sx8725 Semtech Corporation, sx8725 Datasheet - Page 20

• Manufacturer Part Number: sx8725
• Description: Sx8725 Zoomingadc? For Pressure And Temperature Sensing
• Manufacturer: Semtech Corporation

ADVANCED COMMUNICATIONS & SENSING
Programmable Gain Amplifiers
As seen in Figure 8, the zooming function is implemented with three programmable gain amplifiers (PGA).
These are:
All gain and offset settings are realized with ratios of capacitors. The user has control over each PGA activation
and gain, as well as the offset of stages 2 and 3. These functions are examined hereafter.
V1.5 © 2007 Semtech Corp.
PGA2_OFFSET[3:0]
PGA1: coarse gain tuning
PGA2: medium gain and offset tuning
PGA3: fine gain and offset tuning. Should be set ON for high linearity data acquisition
(RegACCfg1[3:0])
(RegACCfg2[5:4])
(RegACCfg2[3:0])
PGA2_GAIN[1:0]
(RegACCfg3[7])
ENABLE[3:0]
PGA1_GAIN
Table 4 - ADC & PGA Enabling
Table 7 - PGA2 Offset Settings
Table 5 - PGA1 Gain Settings
Table 6 - PGA2 Gain Settings
0000
0001
0010
0011
0100
0101
1001
1010
1011
1100
1101
xxx0
xxx1
xx0x
xx1x
x0xx
x1xx
0xxx
1xxx
00
01
10
11
0
1
PGA1 disabled
PGA2 disabled
PGA3 disabled
PGA2 Offset
PGA1 enabled
PGA2 enabled
PGA3 enabled
GDoff
ADC disabled
ADC enabled
PGA1 Gain
PGA2 Gain
GD
GD
Block
+0.2
+0.4
+0.6
+0.8
-0.2
-0.4
-0.6
-0.8
1
2
10
10
+1
-1
1
1
2
5
0
(V/V)
(V/V)
2
ZoomingADC™ for Pressure and Temperature Sensing
(V/V)
20
PGA3_OFFSET[6:0]
(RegACCfg3[6:0])
(RegACCfg4[6:0])
PGA3_GAIN[6:0]
Table 9 - PGA3 Offset Settings
Table 8 - PGA3 Gain Settings
1000010
1010000
0000000
0000001
0000110
0001100
0010000
0100000
1000000
1111111
0000000
0000001
0000010
0010000
0100000
0111111
1000000
1000001
1100000
1111111
...
...
...
...
...
...
...
...
...
...
...
127/12(=10.58)
+1/12(=+0.083)
+63/12(=+5.25)
PGA3 Offset
GDoff
-1/12(=-0.083)
-63/12(=-5.25)
PGA3 Gain
1/12(=0.083)
GD
www.semtech.com
-16/12
+16/12
+32/12
-32/12
12/12
16/12
32/12
64/12
+2/12
-2/12
6/12
3
...
...
...
...
...
...
...
...
0
0
0
3
(V/V)
(V/V)
SX8725