isppac30 Lattice Semiconductor Corp., isppac30 Datasheet - Page 15

• Manufacturer Part Number: isppac30
• Description: In-system Programmable Analog Circuit
• Manufacturer: Lattice Semiconductor Corp.

Lattice Semiconductor
More details about MDAC performance are found in the specifications section of the data sheet. It should be noted
that the specifications of the MDAC’s in regard to bandwidth, gain and offset errors, and drift over temperature are
equivalent to or better than those of the IA’s themselves. This means that in addition to having the same high-
impedance characteristics of the IA’s, the MDAC’s will perform in an equivalent fashion when used in combination
with the IA’s as signal conditioning elements. Predictable performance thereby results when mixing various combi-
nations of input resources together.
Table 2. Outputs vs. Digital Input Code
Increasing MDAC Effective Resolution
Because the value of the ispPAC30’s voltage references can be set to several output voltages, ranging from 64mV
to 2.5V, it is possible to use high-value MDAC settings (>50% full scale) to synthesize most desired thresholds. This
means that a given threshold (32mV or greater) can be set with a resolution of +/-0.8%.
If a higher degree of resolution is needed, the two voltage references and MDACs can be combined in a coarse-
fine adjustment scheme, as shown in Figure 1. In this circuit, VREF1 and MDAC1 provide an adjustment range of
0-2.5V with 19.5mV of resolution, while VREF2 and MDAC2 provide an adjustment range of +/-64mV with 0.5mV of
resolution. By adding these two sources together, a total adjustment range of 0-2.56V with an effective resolution of
0.5mV is achieved.
Figure 1. Coarse-Fine Adjustment using Two References
DEC
127
128
129
160
192
224
254
255
32
64
96
—
—
0
1
Code
HEX
C0
FE
7F
A0
E0
FF
00
01
20
40
60
80
81
—
—
-100.0%
-99.2%
-75.0%
-50.0%
-25.0%
25.0%
50.0%
75.0%
98.4%
99.2%
0.78%
1.56%
-0.8%
0.0%
0.8%
V
MON
MDAC Equivalent Voltage Output vs. VREF Input (in Volts)
0.00025
0.00050
-0.0640
-0.0635
-0.0480
-0.0320
-0.0160
-0.0005
0.0640
0.0000
0.0005
0.0160
0.0320
0.0480
0.0630
0.0635
IN
0.0005
0.0010
-0.128
-0.127
-0.096
-0.064
-0.032
-0.001
0.128
0.000
0.001
0.032
0.064
0.096
0.126
0.127
VREF2=256mV
VREF1=2.5V
-0.256
-0.254
-0.192
-0.128
-0.064
-0.002
ispPAC30
0.256
0.000
0.002
0.064
0.128
0.192
0.252
0.254
0.001
0.002
15
-0.512
-0.508
-0.384
-0.256
-0.128
-0.004
0.512
0.000
0.004
0.128
0.256
0.384
0.504
0.508
0.002
0.004
MDAC1
MDAC2
Comparator Mode
IA2
G=-1
Links Open
-1.024
-1.016
-0.768
-0.512
-0.256
-0.008
1.024
0.000
0.008
0.256
0.512
0.768
1.008
1.016
0.004
0.008
-2.048
-2.032
-1.536
-1.024
-0.512
-0.016
2.048
0.000
0.016
0.512
1.024
1.536
2.016
2.032
0.008
0.016
CP1
-2.5000 Full Scale
-2.4805 Full Scale + 1 lsb
-1.8750
-1.2500
-0.6250
-0.0195 Bipolar Zero - 1 lsb
2.5000
0.0000
0.0195
0.6250
1.2500
1.8750
2.4609
2.4805
0.0098
0.0195
ispPAC30 Data Sheet
OUT1
Bipolar Zero
Bipolar Zero + 1 lsb
+Full Scale - 1 lsb
+Full Scale
1 lsb (with sign)
2 lsb (1 lsb, no sign)
Vref Input (V)