SC2620 datasheet(21/26 Pages) SEMTECH

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SC2620

POWER MANAGEMENT

 2008 Semtech Corp.

Applications Information

For the 1.2V channel:

Ω

⋅









−

)

(

)

(

)

(

⋅

≈

150

)

(

)

550

(

≈

⋅

≈

Bench measurement shows that compensation

components computed from our simplified linear model

give very good load transient response for Channel 1 (Figure

13(a)). However, optimizing load transient for Channel 2

will require a set of compensation component values

different from those calculated above. Loop compensation

networks shown in Figure 1(a) are empirically optimized

for load transients. Figures 13(a) and 13(b) show the

corresponding load transient responses.

Board Layout Considerations

In a step-down switching regulator, the input bypass

capacitor, the main power switch and the freewheeling

diode carry discontinuous currents with high

(Figure

14). For jitter-free operation, the size of the loop formed

by these components should be minimized. Since the power

switches are already integrated within the SC2620,

connecting the anodes of both freewheeling diodes close

to the negative terminal of the input bypass capacitor

minimizes size of the switched current loop. The input

bypass capacitors should be placed close to the PVIN pins.

Shortening the traces of the SW and BOOST nodes reduces

the parasitic trace inductance at these nodes. This not

only reduces EMI but also decreases switching voltage

spikes at these nodes.

The PVIN bypass capacitor C

15, the output filtering

capacitors and the freewheeling diodes are to be grounded

on the power ground plane (Figure 15). The feedback

resistive dividers, the compensation networks, the soft-

OUT

Fast Switching Current Paths in a Buck

Regulator. Minimize the size of this loop

to reduce parasitic trace inductance.

Figure 14.

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