ACT4455 datasheet(9/16 Pages) ACTIVE-SEMI

9 / 16 page

ACT4455

Rev 2, 21-Nov-12

Innovative Power

- 9 -

www.active-semi.com

STABILITY COMPENSATION CONT’D

In the case of high RFB1 used, the frequency

compensation

needs

adjusted

correspondingly. As show in Figure 4, adding a

capacitor in paralled with RFB1 or increasing the

compensation capacitance at COMP pin helps the

system stability.

Figure 3:

Cable Compensation at Various Resistor Divider

Values

Figure 4:

Frequency Compensation for High RFB1

PC Board Layout Guidance

When laying out the printed circuit board, the

following checklist should be used to ensure proper

operation of the IC.

1) Arrange the power components to reduce the

AC loop size consisting of CIN, IN pin, SW pin

and the schottky diode.

2) Place input decoupling ceramic capacitor CIN as

close to IN pin as possible. CIN is connected

power GND with vias or short and wide path.

3) Return FB, COMP and ISET to signal GND pin,

and connect the signal GND to power GND at a

single point for best noise immunity. Connect

exposed pad to power ground copper area with

copper and vias.

4) Use copper plane for power GND for best heat

dissipation and noise immunity.

5) Place feedback resistor close to FB pin.

6) Use short trace connecting HSB-CHSB-SW loop

7) SW pad is noisy node switching from VIN to

GND. It should be isolated away from the rest

of circuit for good EMI and low noise operation.

Delta Output Voltage vs. Output Current

0.6

0.5

0.4

0.3

0.2

0.1

Output Current (mA)

1000

2000

3000

4000

5000

= 3

= 2

RFB

1 =

240

RFB

1 =

200

RFB1

= 15

RFB1 =

100k

RFB1 = 51k

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