ACT4514 datasheet(8/16 Pages) ACTIVE-SEMI

8 / 16 page

ACT4514

Rev 1, 21-Jul-11

Active-Semi

Innovative Power

- 8 -

www.active-semi.com

VOUT

COUT

RCOMP

CCOMP CCOMP2

2.5V

22μF Ceramic

8.2kΩ

2.2nF

None

3.3V

22μF Ceramic

12kΩ

1.5nF

None

22μF Ceramic

15kΩ

1.5nF

None

2.5V

47μF SP CAP

15kΩ

1.5nF

None

3.3V

47μF SP CAP

15kΩ

1.8nF

None

47μF SP CAP

15kΩ

2.7nF

None

2.5V

470μF/6.3V/30mΩ

15kΩ

15nF

47pF

3.3V

470μF/6.3V/30mΩ

15kΩ

22nF

47pF

470μF/6.3V/30mΩ

15kΩ

27nF

47pF

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

≥

−

OUT

ESRCOUT

012

Min

(15)

(Ω)

(16)

COMP

ESRCOUT

OUT

COMP

OUT

COMP

−

(F)

(14)

(13)

(F)

COMP

−

(12)

(Ω)

OUT

808

COMP

OUT

COMP

(11)

COMP2

COMP

(10)

COMP2

COMP

(9)

OUT

(8)

COMP

VEA

(7)

COMP

VEA

OUT

VDC

808

STABILITY COMPENSATION

Figure 4:

Stability Compensation

: CCOMP2 is needed only for high ESR output capacitor

The feedback loop of the IC is stabilized by the

components at the COMP pin, as shown in Figure

3. The DC loop gain of the system is determined by

the following equation:

The dominant pole P1 is due to CCOMP:

The second pole P2 is the output pole:

The first zero Z1 is due to RCOMP and CCOMP:

And finally, the third pole is due to RCOMP and

CCOMP2 (if CCOMP2 is used):

The following steps should be used to compensate

the IC:

STEP 1. Set the cross over frequency at 1/10 of the

switching frequency via RCOMP:

STEP 2. Set the zero fZ1 at 1/4 of the cross over

frequency. If RCOMP is less than 15kΩ, the equation

for CCOMP is:

If RCOMP is limited to 15kΩ, then the actual cross

over frequency is 3.4 / (VOUTCOUT). Therefore:

STEP 3. If the output capacitor’s ESR is high

enough to cause a zero at lower than 4 times the

cross over frequency, an additional compensation

capacitor CCOMP2 is required. The condition for using

CCOMP2 is:

And the proper value for CCOMP2 is:

Though CCOMP2 is unnecessary when the output

capacitor has sufficiently low ESR, a small value

CCOMP2 such as 100pF may improve stability against

PCB layout parasitic effects.

Table 2 shows some calculated results based on

the compensation method above.

Table 1:

Typical Compensation for Different Output

Voltages and Output Capacitors

: CCOMP2 is needed for high ESR output capacitor.

CCOMP2 ≤ 47pF is recommended.

CC Loop Stability

The constant-current control loop is internally

compensated over the 400mA-1500mA output

range. No additional external compensation is

required to stabilize the CC current.

Output Cable Resistance Compensation

To compensate for resistive voltage drop across the

charger's output cable, the ACT4514 integrates a

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