Hello,
My customer is asking if there is any guidance between using a lower REXT resistor value and lower gain control register value to get the same IOUT value compared to higher REXT resistor value and higher gain control register setting.
I did a few calculations and found the minimum and maximum REXT values that can be used and still get 5mA out and found the range to be from 315Ω to 1,250Ω. The only thing I could find is that with lower resistor values there was less power dissipated in REXT compared to higher power dissipated in higher REXT values. See table below:
|
|
Minimum
|
Your Example
|
Maximum
|
|
Rext
|
315
|
619
|
1,250
|
|
Desired IOUT
|
0.005
|
0.005
|
0.005
|
|
IOUT,target
|
0.0050
|
0.0050
|
0.0050
|
|
CM
|
0
|
0
|
0
|
|
HC
|
0
|
0
|
1
|
|
CCn
|
|
|
|
|
CC0
|
0
|
1
|
1
|
|
CC1
|
0
|
1
|
1
|
|
CC2
|
0
|
1
|
1
|
|
CC3
|
0
|
1
|
1
|
|
CC4
|
0
|
1
|
1
|
|
CC5
|
0
|
0
|
1
|
|
D
|
0
|
62
|
63
|
|
VG
|
0.25
|
0.4921875
|
0.9921875
|
|
Vrext
|
0.315
|
0.62015625
|
1.25015625
|
|
Iref
|
0.001000
|
0.001002
|
0.001000
|
|
IOUT,target/Iref
|
5
|
5
|
5
|
|
CG
|
0.08333333
|
0.1640625
|
0.33072917
|
|
power in REXT (mW)
|
0.32
|
0.62
|
1.25
|
Are there any other trade-offs or guidance on this decision that you can share? There are obviously a very large number of options between 315 and 1250Ω.
One other question, does IREF stay on continuously while the part is powered up and not in reset? So when budgeting total power dissipation REXT would be a continuous load?
Thanks!
John
