ACT4501 datasheet(9/16 Pages) ACTIVE-SEMI

9 / 16 page

ACT4501

Rev 2, 14-Nov-12

Innovative Power

- 9 -

www.active-semi.com

STABILITY COMPENSATION CONT’D

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 gives one typical car charger application

schematics and associated BOM list.

Figure 7: PCB Layout

0.3

0.25

0.2

0.15

0.1

0.05

Output Current (mA)

200

400

600

800

1000

Delta Output Voltage vs. Output Current

VIN = 12V

V0UT = 5V

= 3

RFB

= 2

70k

RFB

1 =

240

RFB

1 =

200

RFB1

= 15

RFB1 = 100k

RFB1 = 51

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