Datasheet

P
26
I
D
24
All are S0.23
+
24
24
Saturate
Yn
S2.23 S0.23
24
Shifter
S0.23
24
Yn Scale
Clamp
S0.23
24
Filter Yn
Clamp High
Filter Yn
Clamp Low
Filter Yn
X
24
24
24
Ki_yn reg
Kp Coef
Xn-1 Reg
Xn
16
24
<>
9
9
16
24
24
24
24
24
24
Clamp
Kd yn_reg
Kd alpha
9
16
9
24
24
24
24
P
I
D
Limit Comparator
PID Filter Branch Stages
Ki High
EADC_DATA
9
9
9
9
24
32
Ki Coef
Kd coef
Limit 5
9
9
Limit 6
…..
Limit 0
Coefficient
select
Ki Low
Optional
Selected
by
KI_ADDER_
MODE
Clamp
X
X
X
+
-
+
+
Round
X X +1
n n
–
UCD3138
www.ti.com SLUSAP2F –MARCH 2012–REVISED NOVEMBER 2013
Here is the first section of the Filter :
The filter input, Xn, generally comes from a front end. Then there are three branches, P, I. and D. Note
that the D branch also has a pole, Kd Alpha. Clamps are provided both on the I branch and on the D
alpha pole.
The filter also supports a nonlinear mode, where up to 7 different sets of coefficients can be selected
depending on the magnitude of the error input Xn. This can be used to increase the filter gain for higher
errors to improve transient response.
Here is the output section of the filter (S0.23 means that there is 1 sign bit, 0 integer bits and 23 fractional
bits).:
This section combines the P, I, and D sections, and provides for saturation, scaling, and clamping.
Copyright © 2012–2013, Texas Instruments Incorporated Functional Overview 47
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