BD9302FP-E Datasheet, PDF(12/17 Page) Rohm – A wide input voltage range of 6 V to 18 V, Easy switching frequency setting in the range of 200 k to 2.5 MHz.

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BD9302FP-E Datasheet, PDF (12/17 Pages) Rohm – A wide input voltage range of 6 V to 18 V, Easy switching frequency setting in the range of 200 k to 2.5 MHz.

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For output capacitors having high ESR, such as aluminum electrolytic capacitor

For output capacitors having high ESR (i.e., several ohms), the phase compensation setting procedure becomes

comparatively simple. Since the DC/DC converter application has surely a LC resonant circuit attached to the

output, a -180Ë phase-delay occurs in that area. If ESR component is present there, however, a +90Ë phase-lead

occurs to shift the phase delay to -90Ë. Since the phase delay is desired to set within 150Ë, this is a very effective

method but has a demerit to increase the ripple component of the output voltage.

(3) LC resonant circuit

VCC

(4) With ESR provided

VCC

RESR

fr= 1 [Hz]

2p LC

At this resonance point, a -180Ë

phase-delay occurs.

Fig.29

fr= 1 [Hz]: Resonance point

2p LC

fESR=

[Hz]: Phase lead

2pRESRC

A -90Ë phase-delay occurs.

Fig.30

According to changes in phase characteristics due to the ESR, only one phase lead should be inserted. For this

phase lead, select either of the methods shows below.

(5) Insert feedback resistance in the C.

(6) Insert the R3 in integrator.

R3 C2

Phase lead: fZ=

[Hz]

2pC1R1

Phase lead: fZ=

[Hz]

2pC2R3

Fig.31

Fig.32

For the purpose of canceling the LC resonance, the frequency to insert the phase lead should be set close to the

LC resonant frequency.

For output capacitors having low ESR, such as ceramic capacitor or OS-CON

Unlike the section above, in order to use capacitors having low ESR (i.e., several tens of mW), two phase-leads

should be inserted so that a -180â phase-delay due to LC resonance will be observed. Example (7) blow shows a

typical phase compensation procedure.

(7) Phase compensation with secondary phase lead

C1 R3 C2

Phase lead: fZ1=

[Hz]

2pR1C1

Phase lead: fZ2=

[Hz]

2pR3C2

LC resonant frequency: fr=

2p LC

[Hz]

Fig.33

For the settings of phase lead frequency, insert both of the phase leads close to the LC resonant frequency.

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