ACT4533B datasheet(9/18 Pages) ACTIVE-SEMI

9 / 18 page

ACT4533A/B

Rev 0, 14-Aug-13

Innovative Power

- 9 -

www.active-semi.com

VOUT

COUT

RCOMP CCOMP CCOMP2

2.5V

47μF Ceramic CAP

5.6kΩ

10nF

None

3.3V

47μF Ceramic CAP

8.2kΩ

10nF

None

47μF Ceramic CAP

15kΩ

10nF

None

2.5V

220μF/10V/30mΩ

15kΩ

2.2nF

47pF

3.3V

220μF/10V/30mΩ

15kΩ

2.2nF

47pF

220μF/10V/30mΩ

15kΩ

2.2nF

47pF

(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)

COMP

(9)

OUT

(8)

(7)

COMP

VEA

OUT

VDC

808

STABILITY COMPENSATION

Figure 5:

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

5. 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 6.58 / (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 1 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 1500mA-3500mA 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 ACT4533A/B integrates

a simple, user-programmable cable voltage drop

compensation using the impedance at the FB pin.

Use the curve in Figure 6 to choose the proper

feedback resistance values for cable compensation.

RFB1 is the high side resistor of voltage divider.

COMP

VEA

(

)

OUT

ESRCOUT

006

Min

≥

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