SML2108
PRELIMINARY
ADC SCALING AND OFFSET
The ADC can be customized to monitor a particular range These combinations of scales and offsets allow the reso-
of bias current by programming Register 0. Bits 3 and 2 lution to be maximized over a given range of current. For
controlthescalingoftheADCwhilebits1and0controlthe example, if the bias current is known to be in the range of
ADCoffset. Thefourgraphs(Figures4,5,6,&7)illustrate 30mA to 70mA the choice would be the Half scale graph
the ADC scale values, according to the two bit code. In (code 10BIN) and the ¼ offset curve (code 01BIN) to
eachGraphthecurvesaredifferentiatedbytheADCoffset maximize the resolution of the ADC.
values. Note: if using IBIASP with the maximum current
Note that these graphs assume a full scale bias current of
option set to 10 mA, divide the x-axis value by 10 (i.e., 75
100mA. WhentheADCisconfiguredtoreceiveinputfrom
= 7.5, etc.).
the EXT TEMP pin full scale current becomes 390.6µA,
which limits the internal 1/256 scale factor between bias
current and the ADC input current.
255
224
192
160
128
96
255
224
192
160
128
96
Offset
00
01
10
11
Offset
00
01
10
11
64
64
32
32
0
0
0
10 20 30 40 50 60 70 80 90 100
0
10 20 30 40 50 60 70 80 90 100
I
(mA)
I
(mA)
BIAS
BIAS
2053 Fig04
2053 Fig05
Figure 4. Full Scale (code 11BIN) with Offset
Figure 5. Half Scale (code 10BIN) with Offset
255
224
192
255
224
192
160
128
96
64
32
0
160
Offset
00
01
10
11
Offset
00
01
10
11
128
96
64
32
0
0
10 20 30 40 50 60 70 80 90 100
0
10 20 30 40 50 60 70 80 90 100
I
(mA)
I
(mA)
BIAS
BIAS
2053 Fig06
2053 Fig07
Figure 6. Quarter Scale (code 01BIN) with Offset
Figure 7. Tenth Scale (code 00BIN) with Offset
SUMMIT MICROELECTRONICS, Inc.
2053 2.2 11/07/00
10
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
