SC4601IMSTR datasheet(12/18 Pages) SEMTECH

12 / 18 page

 2006 Semtech Corp.

www.semtech.com

SC4601

POWER MANAGEMENT

Applications Information - (Cont.)

After the compensation, the converter will have the

following loop gain:

)

(

)

(

)

(

COMP

PWM

⋅

Where:

PWM = PWM gain and

M = 1.5V, ramp peak to valley voltage of SC4601.

The design guidelines for the SC4601 applications are

as following:

1. Set the loop gain crossover corner frequency

C for given switching corner frequency

S =2 πfs,

2. Place an integrator at the origin to increase DC

and low frequency gains.

3. Select

Z1 and ωZ2 such that they are placed

near

O to damp the peaking and the loop gain

has a -20dB/dec rate to go across the 0dB

line for obtaining a wide bandwidth.

4. Cancel the zero from C

4’s ESR by a compensa-

tor pole

P1 (ωP1 = ωESR = 1/( RCC4)),

5. Place a high frequency compensator pole

ωp

(

ωp

2 = πfs) to get the maximum attenuation of

the switching ripple and high frequency noise

with the adequate phase lag at

The compensated loop gain will be as given in Figure 4:

-20dB/dec

0dB

ωZ1

ωZ2

ESR

ωo

Loop gain T(s)

Power stage GVD(s)

-40dB/dec

Figure 4. Asymptotic diagrams of power stage and its

loop gain.

Synchronous & Multi-phase Operation

The SC4601 has a SYNC/SLEEP pin, which can be used

to synchronize the controller to a faster external clock.

The SC4601 can be also used in conjunction with

Semtech’s multi-phase link (SC4201), to synchronize and

multi-phase several controllers. Feeding outputs A/B/C/

D of SC4201 to the SYNC inputs of several SC46xx con-

trollers, it is easy to displace the controllers by 2, 3 or 4

phases. Additionally the SC4201 can be synchronized to

an external clock so that everything runs under one fre-

quency. This synchronizing operation avoids frequency

beating among different controllers, simplifies noise fil-

tering. This multi-phasing control displaces the control-

lers by 90o/120o/180o degrees, and simplifies tremen-

dously the input filtering requirements for the system.

Figure 5 shows one possible application.

Figure 5. Breakthrough, innovative solution to meet the

next generation of networking and industrial power re-

quirements.

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