SP6127_07 Datasheet, PDF (5/8 Pages) Sipex Corporation – Evaluation Board Manual

LOOP COMPENSATION
The SP6127 includes Type-II internal compensation components for loop
compensation. External compensation components are not required for systems with
tantalum or aluminum electrolytic output capacitors with sufficiently high ESR. Use the
condition below as a guideline to determine whether or not the internal compensation is
sufficient for your design.
Type-II internal compensation is sufficient if the following condition is met:
f < f _ESRZERO
DBPOLE
………………. (1)
where:
1
f _ESRZERO = _{2.π .RESR .COUT} ……….. (2)
1
f _DBPOLE = _{2.π . L ⋅ COUT} ………… (3)
Creating a Type-III compensation Network
The above condition requires the ESR zero to be at a lower frequency than the double-
pole from the LC filter. If this condition is not met, Type-III compensation should be
used and can be accomplished by placing a series RC combination in parallel with R1
as shown below. The value of CZ can be calculated as follows and RZ selected from
table 1.
CZ = ^{L ⋅ C} ………….. (4)
1.25 × R1
f_ESRZERO/f_DBPOLE RZ
1X
50K
2X
40K
3X
30K
5X
10K
>= 10X
2K
Table1- Selection of RZ
5