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ACT4060A Datasheet(PDF) 6 Page - Active-Semi, Inc |
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ACT4060A Datasheet(HTML) 6 Page - Active-Semi, Inc |
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6 / 12 page  ACT4060A Rev 1, 25-Jun-09 Innovative Power TM - 6 - www.active-semi.com Copyright © 2009 Active-Semi, Inc. VOUT COUT RCOMP CCOMP 2.5V 22μF Ceramic 8.2kΩ 2.2nF 3.3V 22μF Ceramic 12kΩ 1.5nF 5V 22μF Ceramic 15kΩ 1.5nF 2.5V 47μF SP CAP 15kΩ 1.5nF 3.3V 47μF SP CAP 15kΩ 1.8nF 5V 47μF SP CAP 15kΩ 2.7nF 2.5V 470μF/6.3V/30mΩ 15kΩ 15nF 3.3V 470μF/6.3V/30mΩ 15kΩ 22nF 5V 470μF/6.3V/30mΩ 15kΩ 27nF (12) (Ω) ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × × ≥ − OUT OUT 6 ESRCOUT V 012 . 0 , C 10 1 . 1 Min R OUT OUT 5 COMP C V 10 2 . 1 C − × = (F) (11) (10) (F) COMP 5 COMP R 10 8 . 1 C − × = (9) (Ω) OUT OUT 8 C V 10 7 . 1 × = V 3 . 1 G G 10 f C V π 2 R COMP EA SW OUT OUT COMP × = (7) COMP COMP 1 Z C R 2 1 f π = (6) OUT OUT OUT 2 P C V π 2 I f = (4) COMP VEA OUT VDC G A I V 3 . 1 A = COMP CCOMP2 CCOMP RCOMP ACT4060A COMP ESRCOUT OUT 2 COMP R R C C = (13) COMP2 COMP 3 P C R π 2 1 f = (8) (5) COMP VEA EA 1 P C A π 2 G f = STABILITY COMPENSATION Figure 2: 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 2. 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: but limit RCOMP to 15kΩ maximum. 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 2: Typical Compensation for Different Output Voltages and Output Capacitors Figure 4 shows an example ACT4060A application circuit generating a 3.3V/2A output. |
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