NCP1410_05 datasheet(12/14 Pages) ONSEMI

部品番号	NCP1410

部品情報	250 mA Sync-Rect PFM Step-Up DC-DC Converter with Low-Battery Detector

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NCP1410

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12

GENERAL DESIGN PROCEDURES

Switching mode converter design is considered as black

magic to most engineers, some complicate empirical

formulae are available for reference usage. Those formulae

are derived form the assumption that the key components,

i.e. power inductor and capacitors are available with no

tolerance. Practically, its not true, the result is not a matter

of how accurate the equations you are using to calculate the

component values, the outcome is still somehow away from

the optimum point. In below a simple method base on the

most basic first order equations to estimate the inductor and

capacitor values for NCP1410 operate in Continuous

Conduction Mode is introduced. The component value set

can be used as a starting point to fine tune the circuit

operation. By all means, detail bench testing is needed to get

the best performance out of the circuit.

Design Parameters:

VIN = 1.8 V to 3.0 V, Typical 2.4 V

VOUT = 3.3 V

IOUT = 200 mA (250 mA max)

VLB = 2.0 V

VOUT−RIPPLE = 40 mVP−P at IOUT = 250 mA

Calculate the feedback network:

Select RFB2 = 200 K

RFB1

+ RFB2

VOUT

VREF

* 1

RFB1 + 200 K

3.3 V

1.19 V

* 1 + 355 K

Calculate the Low Battery Detect divider:

VLB = 2.0 V

Select RLB2 = 330 K

RLB1 + RLB2

VLB

VREF

* 1

RLB1 + 330 K

2.0 V

1.19 V

* 1 + 225 K

Determine the Steady State Duty Ratio, D for typical VIN,

operation will be optimized around this point:

VOUT

VIN

+

1

* D

D

+ 1 *

VIN

VOUT

+ 1 * 2.4 V

3.3 V

+ 0.273

Determine the average inductor current, ILAVG at

maximum IOUT:

ILAVG +

IOUT

1

* D +

250 mA

1

* 0.273 +

344 mA

Determine the peak inductor ripple current, IRIPPLE−P and

calculate the inductor value:

Assume IRIPPLE−P is 20% of ILAVG, the inductance of the

power inductor can be calculated as in below:

IRIPPLE−P = 0.20 x 344 mA = 68.8 mA

L

+

VIN

tON

2IRIPPLE * P

+

2.4 V

1.4

mS

2(68.8 mA)

+ 24.4 mH

Standard value of 22

mH is selected for initial trial.

Determine the output voltage ripple, VOUT−RIPPLE and

calculate the output capacitor value:

VOUT−RIPPLE = 40 mVP−P at IOUT = 250 mA

COUT u

IOUT

tON

VOUT−RIPPLE * IOUT

ESRCOUT

where tON = 1.4

mS and ESRCOUT = 0.1 W,

COUT u

250 mA

1.4

mS

40 mV

* 250 mA

0.1

W +

23.33

mF

From above calculation, you need at least 23.33

mF in

order to achieve the specified ripple level at conditions

stated. Practically, a one level larger capacitor will be used

to accommodate factors not take into account in the

calculation, therefore a capacitor value of 33

mF is selected.

同様の部品番号 - NCP1410_05

メーカー	部品番号	データシート	部品情報
ON Semiconductor	NCP1410DMR2	126Kb / 16P	250 mA Sync-Rect PFM Step-Up DC-DC Converter with Low-Battery Detector December, 2001 ??Rev. 2

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