2.2MHz, Dual-Output Buck or Boost Converter

with Internal Power MOSFETs

______________________________________________________________________________________

21

Boost Converter Compensation

The boost converter compensation gets complicated

The right-half-plane zero causes a drop in-phase while

adding positive (+1) slope to the gain curve. It is impor-

tant to drop the gain significantly below unity before the

RHP frequency. Use the following procedure to calcu-

late the compensation components.

the right half plane zero frequency.

where:

Target the unity-gain crossover frequency for:

2) Place a zero

≥ 10kΩ.

C

fR

F

LC

F

=

××

×

1

20 75

π

.

()

f

RC

Z

FF

1

1

2

=

××

π

f

f

C

ZERO RHP

≤

,

5

D

V

V

R

V

I

IN

OUT

MIN

OUT

OUT MAX

=−

=

1

()

()

f

D

LC

f

DR

L

LC

OUT OUT

ZERO RHP

MIN

OUT

=

−

×

=

−

×

1

2

1

2

2

π

π

,

()

()

VL

CLOCK

OUT

OUTPUT2

OUTPUT1

3.3V/2A

VL

INPUT

SYSTEM

CLOCK

INPUT

OUTPUT2

12V/0.2A

28

27

26

25

24

23

22

8

9

10

11

12

13

14

15

16

17

18

19

20

21

7

6

5

4

3

2

1

BST2/VDD2

CLKOUT

DRAIN2

DRAIN2

EN2

ON

OFF

FB2

COMP2

SOURCE2 PGND

PGND

SGND

SGND

PGOOD2

SOURCE1

PGOOD1

BST1/VDD1

DRAIN1

DRAIN1

EN1

FB1

COMP1

BYPASS

VL

VL

V+

OSC

N.C.

SYNC

ON

*CONNECT PGND AND SGND TOGETHER AT ONE POINT NEAR

THE RETURN TERMINALS OF THE V+ AND VL BYPASS CAPACITORS.

OFF

PGOOD2

PGOOD1

OUTPUT1

MAX5073

SGND

EP

Figure 8. Buck-Boost Application