BD95710MUV

Technical Note

10/20

www.rohm.com

2009.04 - Rev.B

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6. Setting output voltage

The output voltage is REFIN/EN = VOUT when VOUT is tied to the FB directly. The range of VOUT is 0.4V ~ 3.3V.

REFIN/EN

The output voltage is calculated as follow when resistor divider network is connected between the FB and VOUT.

REFIN/EN set 5Vcc.

Vout =

x 0.6 [V]・・・(12)

7. Frequency Setting Resistance

The Frequency at steady state is determined by resistance value connected to RT pin.

But actual PHASE rising time and falling time are factored in due to the external MOSFET gate capacity or switching speed.

As a result, On-Time increases.

The frequency is determined by the following formula.

Consequently, total frequency becomes lower than the formula above.

On-Time increases by Dead Time on the condition of zero cross point of inductor current. And also switching frequency

increases as the output current increases due to the fixed On-Time and the influence of conduction loss.

It is recommended that switching frequency be checked on large current condition (at the point where the inductor current

doesn’t become reversed from Vout).

FB

H

CONTROLLA

S

RQ

Driver

Circuit

VOUT

BUSEN

R1+R2

R2

f [Hz]=

×

10

VIN

・・・

(13)

H

CONTROLLA

S

RQ

Driver

Circuit

VOUT

BUSEN

FB

R1

R2

0.6V

VOUT

Ton

1

Ton =

+ 170×10

-9

2×BUSEN

Ton : ON TIME