Part Number: PGA280
Other Parts Discussed in Thread: PGA281
Dear Team,
My customer is considering to use the PGA280, then they would like to have the following characteristics data.
a) Vos/℃ at each Gain setting
b) Ibias/℃ at each Gain setting
c) Ioffset/℃ at each Gain setting (Characteristics curve is OK)
Although the typical values of G=1 and G=128 are listed in the datasheet, they would like to confirm the data for other gains.
Best Regards,
Koshi Ninomiya
Hi Carolina-san,
The customer would like to know the following about the PGA280.
For example, can you tell if there is a gain setting that is worse than when G=1? 
Best Regards,
Koshi Ninomiya
Hi Ninomiya-san,
The PGA280 and the PGA281 have the same core but are different in how the gain is set (pin programmable vs SPI).
The PGA281 datasheet shows an equation for the offset voltage and the offset voltage drift:
If I were to calculate the offset voltage drift for all gains using this equation for the PGA281, I would get the following results:
| Offset voltage vs temp, RTI (uV/C) | ||||
| Gain | Typ (+) | Typ (-) | Max (+) | Max (-) |
| 0.125 | 1.470 | -1.470 | 3.770 | -3.770 |
| 0.172 | 1.077 | -1.077 | 2.786 | -2.786 |
| 0.25 | 0.750 | -0.750 | 1.970 | -1.970 |
| 0.344 | 0.553 | -0.553 | 1.478 | -1.478 |
| 0.5 | 0.390 | -0.390 | 1.070 | -1.070 |
| 0.688 | 0.292 | -0.292 | 0.824 | -0.824 |
| 1 | 0.210 | -0.210 | 0.620 | -0.620 |
| 1.375 | 0.161 | -0.161 | 0.497 | -0.497 |
| 2 | 0.120 | -0.120 | 0.395 | -0.395 |
| 2.75 | 0.095 | -0.095 | 0.334 | -0.334 |
| 4 | 0.075 | -0.075 | 0.283 | -0.283 |
| 5.5 | 0.063 | -0.063 | 0.252 | -0.252 |
| 8 | 0.053 | -0.053 | 0.226 | -0.226 |
| 11 | 0.046 | -0.046 | 0.211 | -0.211 |
| 16 | 0.041 | -0.041 | 0.198 | -0.198 |
| 22 | 0.038 | -0.038 | 0.190 | -0.190 |
| 32 | 0.036 | -0.036 | 0.184 | -0.184 |
| 44 | 0.034 | -0.034 | 0.180 | -0.180 |
| 64 | 0.033 | -0.033 | 0.177 | -0.177 |
| 88 | 0.032 | -0.032 | 0.175 | -0.175 |
| 128 | 0.031 | -0.031 | 0.174 | -0.174 |
| 176 | 0.031 | -0.031 | 0.173 | -0.173 |
As you can see the offset voltage drift is higher for lower gains and matches (in a more conservative way) what is specified in the PGA280 datasheet.
This trend however is shown in RTI (or referred to input, which means it measured at the output and divided by the gain of the device). When the gain is an attenuation (less than 1) as is the case of the PGA280/281 - it can be deceiving.
I have done the same calculation but referring to the output so you can see how much of the error is seen at the output:
| RTO | ||||
| Gain | Typ (+) | Typ (-) | Max (+) | Max (-) |
| 0.125 | 0.184 | -0.184 | 0.471 | -0.471 |
| 0.172 | 0.185 | -0.185 | 0.479 | -0.479 |
| 0.25 | 0.188 | -0.188 | 0.493 | -0.493 |
| 0.344 | 0.190 | -0.190 | 0.508 | -0.508 |
| 0.5 | 0.195 | -0.195 | 0.535 | -0.535 |
| 0.688 | 0.201 | -0.201 | 0.567 | -0.567 |
| 1 | 0.210 | -0.210 | 0.620 | -0.620 |
| 1.375 | 0.221 | -0.221 | 0.684 | -0.684 |
| 2 | 0.240 | -0.240 | 0.790 | -0.790 |
| 2.75 | 0.263 | -0.263 | 0.918 | -0.918 |
| 4 | 0.300 | -0.300 | 1.130 | -1.130 |
| 5.5 | 0.345 | -0.345 | 1.385 | -1.385 |
| 8 | 0.420 | -0.420 | 1.810 | -1.810 |
| 11 | 0.510 | -0.510 | 2.320 | -2.320 |
| 16 | 0.660 | -0.660 | 3.170 | -3.170 |
| 22 | 0.840 | -0.840 | 4.190 | -4.190 |
| 32 | 1.140 | -1.140 | 5.890 | -5.890 |
| 44 | 1.500 | -1.500 | 7.930 | -7.930 |
| 64 | 2.100 | -2.100 | 11.330 | -11.330 |
| 88 | 2.820 | -2.820 | 15.410 | -15.410 |
| 128 | 4.020 | -4.020 | 22.210 | -22.210 |
| 176 | 5.460 | -5.460 | 30.370 | -30.370 |
Now a new trend emerges that shows that as the gain gets bigger, so does the error.
Here is the excel I used to make all these calculations: offset_drift_calculations.xlsx
All the best,
Carolina
