SC4614 데이터 시트보기 (PDF) - Semtech Corporation

부품명

상세내역

일치하는 목록

SC4614

500kHz Voltage Mode PWM Controller

Semtech Corporation 

SC4614

POWER MANAGEMENT

Applications Information (Cont.)

60

30

Fz1

0

-30

Fp1 COM PENSATOR GAI N

Fp2

Fz2

Fo

Fz

LOOP GAIN

CONV ERTER GAI N

Fc

-60

100

1K

10K

100 K

FR EQ UENCY (Hz )

Fig. 4. Bode plots for control loop design

(2). Select the open loop crossover frequency Fc located

at 10% to 20% of the switching frequency. At Fc, find the

required DC gain.

(3). Use the first compensator pole Fp1 to cancel the

ESR zero Fz.

(4). Have the second compensator pole Fp2 at half the

switching frequency to attenuate the switching ripple and

high frequency noise.

(5). Place the first compensator zero Fz1 at or below

50% of the power stage resonant frequency Fo.

(6). Place the second compensator zero Fz2 at or below

1M

the power stage resonant frequency Fo.

A MathCAD program is available upon request for the

calculation of the compensation parameters.

C2

LAYOUT GUIDELINES

C1

R2

Vc

2

1

3

VREF

0. 5V

C3

R3

Rt op

Rb ot

The switching regulator is a high di/dt power circuit. Its

Printed Circuit Board (PCB) layout is critical. A good lay-

Vo out can achieve an optimum circuit performance while

minimizing the component stress, resulting in better sys-

tem reliability. During PCB layout, the SC4614 controller,

MOSFETs, inductor, and power decoupling capacitors have

to be considered as a unit.

The following guidelines are typically recommended for

using the SC4614 controller.

Fig. 5. Compensation network

The top resistor Rtop of the voltage divider in Fig. 5 can

be chosen from 1k to 5k. Then the bottom resistor Rbot

is found from:

Rbot

=

0.5V

VO - 0.5V

× Rtop

where 0.5V is the internal reference voltage of the

SC4614.

(1). Place a 4.7uF to 10uF ceramic capacitor close to

the drain of top MOSFET for the high frequency and high

current decoupling. The loop formed by the capacitor,

the top and bottom MOSFETs must be as small as pos-

sible. Keep the input bulk capacitors close to the drain

of the top MOSFETs.

(2). Place the SC4614 over a quiet ground plane to avoid

pulsing current noise. Keep the ground return of the gate

drive short.

(3). Connect bypass capacitors as close as possible to

the decoupling pins (DRV and Vcc) to the ground pin GND.

The trace length of the decoupling capacitor on DRV pin

should be no more than 0.2” (5mm).

The other components of the compensator can be cal- (4). Locate the components of the bootstrap circuit close

culated using following design procedure:

to the SC4614.

(1). Plot the converter gain, including LC filter and PWM

modulator.

 2005 Semtech Corp.

9

www.semtech.com

Share Link: