SC2453ITSTR datasheet(9/14 Pages) SEMTECH

9 / 14 page

 2002 Semtech Corp.

www.semtech.com

SC2453

POWER MANAGEMENT

PRELIMINARY

Applications Information (Cont.)

PWM CONTROLLER

SC2453 is a voltage mode buck controller that utilizes

an externally compensated high bandwidth error ampli-

fier to regulate output voltage. The power stage of the

synchronous rectified buck converter control-to-output

transfer function is as shown below:

)

(

where,

O =

L – Output inductance

C – Output capacitance

C – Output capacitor ESR

IN – Input voltage

Vref

Figure 1. Voltage Mode Buck Converter Compensation

Network

The transfer function of the compensation network is as

follows:

)

)(

(

)

)(

(

)

(

COMP

⋅

where,

)

(

)

(

The design guidelines are as following:

1. Set the loop gain crossover frequency

C for given

switching frequency.

2. Place an integrator in the origin to increase DC and

low frequency gains.

3. Select

Z1 and ωZ2 such that they are placed near ωO

to dampen peaking; the loop gain has –20dB rate

to go across the 0dB line for obtaining a wide band-

width.

4. Cancel

ESR with compensation pole ωP1 (ωP1 = ωESR ).

5. Place a high frequency compensation pole

P2 at the

half switching frequency to get the maximum attenu-

ation of the switching ripple and the high frequency

noise with the adequate phase lag at

Figure 2. Asymptotic diagram of buck power stage and

its compensated loop gain.

0dB

ωZ1

ESR

ω o

Loop gain T(s)

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