5

LOOP COMPENSATION

The SP6126 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:

DBPOLE

ESRZERO

f

f

<

………………. (1)

where:

OUT

ESR

ESRZERO

C

R

f

.

.

.

2

1

π

=

……….. (2)

OUT

DBPOLE

C

L

f

⋅

=

.

.

2

1

π

………… (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.

1

R

C

L

CZ

⋅

=

………….. (4)

Table1- Selection of RZ

1X

50K

2X

40K

3X

30K

5X

10K

>= 10X

2K