LV5768V データシートの表示（PDF） - SANYO -> Panasonic

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LV5768V

1-channel Step-down Switching Regulator

SANYO -> Panasonic 

LV5768V

Irip_out =

1

23

×

VOUT (VIN - VOUT)

L × fOSC × VIN

[Arms]

(18)

It is advisable to use ceramic capacitor in combination with electrolytic capacitor to reject high frequency noise. The

electrolytic capacitor can be low ESR aluminum electrolytic capacitor or polymer aluminum electrolytic capacitor.

9) Inductor selection

L1: Caution is required due to the heat generation from choke coil caused by overload and load short. The inductance

value is determined by output ripple voltage (Vrip) and the impedance of output capacitor for switching frequency.

The minimum inductance is obtained by the equation (19).

L min =

VIN - VOUT

fOSC × VIN

×

VOUT × RC

Vrip

[µH]

(19)

In the above equation, ESR is used in place of the impedance of output capacitor. The reason is, the impedance of

output capacitor for switching frequency is close to RC in many cases. However with ceramic capacitor, real

impedance is used instead of RC.

Ex)VIN(max)=24V, VOUT=12V, Vrip=100mV, RC=9mΩ, fOSC=100kHz

L min =

24V - 12V

100k × 24V

×

12V × 9m

20mV

(20)

≈ 27 [µH]

In the actual part selection, ripple voltage is defined first, then capacitor and inductor are selected. Take the

maximum value and minimum value of input voltage, output voltage and load variation into consideration. Also, the

ripple current of inductor is used as basis for output inductor selection in many cases. Ripple current is obtained by

the equation (21).

Irip

=

VIN - VOUT

fOSC × L

×

D

[A]

(21)

D represents duty cycle defined by VOUT/VIN.

The important term is the ripple current represented as Irip/IOUT. As long as the ripple element is less than 50%, it

should not be a problem. If the ripple element is higher, inductor loss becomes significant.

Ex)VIN=24V, VOUT=12V, fOSC=100kHz, L=45μH

Irip =

24V - 12V

100k × 45µ

× 0.5

(22)

= 1.3 [A]

10) Power consumption of high side MOSFET

The power consumption in the external high side MOSFET is represented by conduction loss and switching loss.

The conduction loss of MOSFET is obtained by the following equation (23).

Psat = IO2 × RDS(ON) × D [W]

(23)

Since RDS(ON) is affected by temperature, it is advisable to confirm the actual FET temperature and data sheet.

The switching loss of high side MOSFET is obtained by the following equation (24).

Psw = VIN × IO × tSW × fSW [W]

(24)

IO: DC output current

tSW: Rise time of switching waveform

fSW: Switching frequency

PS No.A2093-12/15

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