SC4910B datasheet(11/19 Pages) SEMTECH

11 / 19 page

 2005 Semtech Corp.

www.semtech.com

SC4910A/B

POWER MANAGEMENT

Type 2 compensator (Figure 3) is needed for the above

current mode control. The compensation network gives

the following characteristics:

COMP

Figure 3

where

)

(

The loop gain will be given by:

ref

vgo

COMP

•

Figure 4

Applications Information (Cont.)

The goal of the compensation design is to shape the loop

with high DC gain, high bandwidth, enough phase margin,

and high attenuation for high frequency noises. Figure 4

gives the asymptotic diagrams of the power stage with

current loop closed and its loop gain.

One integrator is added to increase the DC gain. W

zc is

used to cancel the power stage pole w

p so that the loop

gain has –20dB rate when it reaches 0 dB line. w

pc is

placed at output capacitor ESR or half switching frequency,

whichever is lower.

Arbitrarily choose R2, then

)

(

−

I is adjusted for satisfactory phase margin and

crossover frequency.

Synchronization

Synchronization of oscillators in multiphase operation

allows for reduced size of filtering components and

improved dynamic response.

SC4910 provides single stage conversion where SC4201

provides the multiphase function. SC4910 and SC4201

are placed on the secondary side, outputs A and C of the

SC4201 are fed into the Sync pins of 2 separate

SC4910’s. Both power supplies operate 180 degrees

apart. SC4201 can be configured up to 4 phase

operation.

Vref

Loop gain T(s)

Power stage

Compensator

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