20

 2006 Semtech Corp.

www.semtech.com

SC2620

POWER MANAGEMENT

Applications Information

gain at high frequency. Placing p

2

S

ω

gives:

5

6

fR

1

C

π

≈

(13)

Computed R

load transient responses in over half of the applications.

However in other cases empirically determined

compensation networks based on optimized load transient

responses may differ from those calculated by a factor of

3. Therefore checking the transient response of the

converter is imperative. Starting with calculated R

and C

expected load step to the converter at the maximum

operating V

converter while adjusting R

R

waveform does not show excessive ringing or overshoot

(see Figures 13(a), 13(b), 16(b) and 16(c)).

Feedforward capacitor C

limited frequency range and is sometimes used to improve

loop response. C

2

1

1

R

R

R



>>

.

Upper Trace : OUT1 Voltage, AC Coupled, 0.5V/div

Lower Trace : L

Upper Trace : OUT2 Voltage, AC Coupled, 0.5V/div

Lower Trace : L

40

µs/div

40

µs/div

(a)

(b)

V

V

V

V

Example: Determine the compensation components for

the 550kHz 9V-16V to 3.3V and 1.2V converter in Figure

1(a).

For both channels,

1

S

Mrads

5

.

3

−

=

ω

,

A

2

I

)

MAX

(

OUT

=

and

F

22

C

1

µ

=

. n is assumed to be 1 in (11) and (12).

For the 3.3V output:

Ω

=

×

⋅

⋅

⋅

×

⋅

×









+

=

−

−

k

3

.

11

)

10

8

.

2

(

)

8

(

)

1

(

10

10

22

10

5

.

3

k

13

k

1

.

30

1

R

4

6

6

5

nF

5

.

1

10

5

.

5

2

k

3

.

11

60

C

5

5

=

×

⋅

π

⋅

≈

pF

47

)

10

3

.

11

(

)

10

550

(

1

C

3

3

6

≈

×

⋅

×

⋅

π

≈

Figure 13. Load Transient Response of the Dual DC-DC Converter in Figure 1(a). I

between 0.3A and 2A.