MIC2141BM5 データシートの表示（PDF） - Micrel

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MIC2141BM5

Micropower Boost Converter

Micrel 

Micrel, Inc.

Application Information

Pre-designed circuit information is at the end of this

section.

Component Selection

Boost Inductor

Maximum power is delivered to the load when the

oscillator is gated on 100% of the time. Total output

power and circuit efficiency must be considered when

determining the maximum inductor. The largest inductor

possible is preferable in order to minimize the peak

current and output ripple. Efficiency can vary from 80%

to 90% depending upon input voltage, output voltage,

load current, inductor, and output diode.

Equation 1 solves for the output current capability for a

given inductor value and expected efficiency. Figures 5

through 9; graph estimates for maximum output current,

assuming the minimum duty cycle, maximum frequency,

and 85% efficiency. To determine the required

inductance, find the intersection between the output

voltage and current and select the value of the inductor

curve just above the intersection. If the efficiency is

expected to be other than the 85% used for the graph,

Equation 1 can then be used to better determine the

maximum output capability.

(1)

( ) IO(max) =

VIN(min) t ON 2 ×

1

2LMAX TS

VO

eff

− VIN(min)

The peak inductor and switch current can be calculated

from Equation 2 or read from the graph in Figure 10. The

peak current shown in Figure 10 is derived assuming a

maximum duty cycle and a minimum frequency. The

selected inductor and diode peak current capability must

exceed this value. The peak current seen by the inductor

is calculated at the maximum input voltage. A wider input

voltage range will result in a higher worst-case peak

current in the inductor. This effect can be seen in Table

4 by comparing the difference between the peak current

at VIN(min) and VIN(max).

(2)

IPK

=

t ON(max) VIN(max)

L MIN

DCM/CCM Boundary

Equation 3 solves for the point at which the inductor

current will transition from DCM (discontinuous conduc-

tion mode) to CCM (continuous conduction mode). As

the input voltage is raised above this level the inductor

has a potential for developing a dc component while the

oscillator is gated on. Table 1 displays the input points at

which the inductor current can possibly operate in the

CCM region. Operation in this region can result in a peak

current slightly higher than displayed on Table 4.

December 2006

MIC2141

VOUT

3.3V

5.0V

9.0V

12.0V

15.0V

16.0V

20.0V

22.0V

VIN(CCM)

3.04V

4.40V

7.60V

10.0V

12.4V

13.2V

16.4V

18.0V

Table 1. DCM/CCM Boundary

(3)

VIN(ccm) = (VOUT + VFWD) + (1 – D)

Table 2 lists common inductors suitable for most applica-

tions. Table 6 lists minimum inductor sizes versus input

and output voltage. In low-cost, low-peak-current applic-

ations, RF-type leaded inductors may sufficient. All

inductors listed in Table 4 can be found within the

selection of CR32- or LQH4C-series inductors from

either Sumida or muRata.

Manufacturer

MuRata

Sumida

J.W. Miller

Coilcraft

Series

LQH1C/C3/C4

CR32

78F

90

Device Type

surface mount

surface mount

axial leaded

axial leaded

Table 2. Inductor Examples

Boost Output Diode

Speed, forward voltage, and reverse current are very

important in selecting the output diode. In the boost

configuration, the average diode current is the same as

the average load current. (The peak current is the same

as the peak inductor current and can be derived from

Equation 2 or Figure 10.) Care must be take to make

sure that the peak current is evaluated at the maximum

input voltage.

Diode

MBR0530

1N4148

BAT54

BAT85

75°C

VFWD

at

100mA

0.275V

0.6V

(175°C)

0.4V

(85°C)

0.54V

(85°C)

25°C

VFWD

at

100mA

0.325V

0.95V

0.45V

0.56V

Room

Temp.

Leakage

at 15V

2.5µA

25nA

(20V)

10nA

(25V)

0.4µA

75°C

Leakage

at 15V

90µA

0.2µA

(20V)

1µA

(20V)

2µA

(85°C)

Package

SOD123

SMT

leaded

and SMT

SMT

DO-34

leaded

Table 3. Diode Examples

7

M9999-122006

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