ACT4514 datasheet(9/16 Pages) ACTIVE-SEMI

9 / 16 page

ACT4514

Rev 1, 21-Jul-11

Active-Semi

Innovative Power

- 9 -

www.active-semi.com

STABILITY COMPENSATION CONT’D

simple, user-programmable cable voltage drop

compensation using the impedance at the FB pin.

Use the curve in Figure 4 to choose the proper

feedback resistance values for cable compensation.

RFB1 is the high side resistor of voltage divider.

In the case of high RFB1 used, the frequency

compensation

needs

adjusted

correspondingly. As show in Figure 6, adding a

capacitor in paralled with RFB1 or increasing the

compensation capacitance at COMP pin helps the

system stability.

Figure 5:

Cable Compensation at Various Resistor Divider

Values

Figure 6:

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.

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

Figure 7 shows an example of PCB layout.

Figure 8 and Figure 9 give two typical car charger

application schematics and associated BOM list.

0.48

0.4

0.32

0.24

0.16

0.08

0.56

0.64

Output Current (mA)

250

500

750

1000

1250

1500

Delta Output Voltage vs. Output Current

= 3

RFB

= 2

RFB

1 =

150

RFB1

= 10

RFB1 =

68k

RFB1 = 12

VIN = 14V

V0UT = 5V

IISET = 1.5A

= 2

Figure 7: PCB Layout

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