BD8964FVM-TR Просмотр технического описания (PDF) - ROHM Semiconductor

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производитель

BD8964FVM-TR

4.0V to 5.5V, 1.2A 1ch Synchronous Buck Converter with Integrated FET

ROHM Semiconductor 

BD8964FVM

Datasheet

6. Selection of Components Externally Connected

(1) Selection of Inductor (L)

IL

ΔIL

VCC

IL

VOUT

L

CO

Figure 26. Output Ripple Current

The inductance significantly depends on output ripple current.

As shown in equation (1), the ripple current decreases as the

inductor and/or switching frequency increases.

I L



VCC  VOUT

L VCC

  VOUT

f

A ・・・(1)

Appropriate ripple current at output should be +/-30% of the

maximum output current.

  IL  0.3IOUTMax A ・・・(2)

L



VCC VOUTVOUT

IL VCC f

Where:

H ・・・(3)

ΔIL is the Output ripple current, and

f is the Switching frequency

Note: Current exceeding the current rating of the inductor results in magnetic saturation of the inductor, which decreases

efficiency.

The inductor must be selected allowing sufficient margin with which the peak current may not exceed its current

rating.

If VCC=5V, VOUT=1.5V, f=1MHz, ∆IL=0.3A x 0.8A=0.24A, for example,

L



5 1.51.5

0.24 51M



4.375



4.7

H 

Note: Select an inductor with low resistance component (such as DCR and ACR) to minimize dissipation in the inductor

for better efficiency.

(2) Selection of Output Capacitor (CO)

VCC

Output capacitor should be selected with the consideration on the stability

region and the equivalent series resistance required to minimize ripple voltage.

Output ripple voltage is determined by the equation (4)

VOUT

VOUT  IL  ESR V  ・・・(4)

L

ESR

Where:

CO

ΔIL is the Output ripple current, and

ESR is the Equivalent series resistance of output capacitor

Figure 27. Output Capacitor

Note: Rating of the capacitor should be determined allowing sufficient margin

against output voltage. Less ESR allows reduction in output ripple voltage.

Since output rise time is designed to fall within the soft-start time, the capacitance of output capacitor should be

determined by the requirements of equation (5):

CO



tSS

 (ILIMIT 

VOUT

IOUT

)

Where:

・・・(5)

tSS: Soft-Start time

ILIMIT: Over current detection level, 2A(Typ)

In case of BD8964FVM, for instance, and if VOUT=1.5V, IOUT=0.8A, and tSS=1ms,

CO



1m  (2  0.8)

1.5



800

F 

Rating of the capacitor should be determined to allow a sufficient margin against output voltage. A 10μF to 100μF

ceramic capacitor is recommended.

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