SC2620 datasheet(20/26 Pages) SEMTECH

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 2006 Semtech Corp.

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SC2620

POWER MANAGEMENT

Applications Information

gain at high frequency. Placing p

3 at about

gives:

≈

(13)

Computed R

5, C5 and C6 can indeed result in near optimal

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

5, C5

and C

6 (using n=1 in Equations (11)-(13)), apply the largest

expected load step to the converter at the maximum

operating V

IN. Observe the load transient response of the

converter while adjusting R

5, C5 and C6. Choose the largest

5, the smallest C5 and C6 so that the inductor current

waveform does not show excessive ringing or overshoot

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

Feedforward capacitor C

11 boosts phase margin over a

limited frequency range and is sometimes used to improve

loop response. C

11 will be more effective if



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

Lower Trace : L

1 Inductor Current, 0.5A/div

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

Lower Trace : L

2 Inductor Current, 0.5A/div

µs/div

(a)

(b)

OUT=3.3V

IN=16V

OUT=1.2V

IN=16V

Example: Determine the compensation components for

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

1(a).

For both channels,

Mrads

−

)

MAX

(

OUT

and

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

For the 3.3V output:

Ω

⋅









−

)

(

)

(

)

(

⋅

≈

)

(

)

550

(

≈

⋅

≈

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

OUT1 and IOUT2 are switched

between 0.3A and 2A.

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