Analog Integrated Circuit Device Data



Freescale Semiconductor

38

BC3770

6.1.2

Application Instructions

6.1.2.1

Determine the Inductor, L

Selecting the proper inductor value is a critical design step for a DC-DC converter.

current with a 1.0 A output current, LIR = 0.3 A/1.0 A = 0.3).

Depending on the desired load transient performance, LIR can be set between 0.2 and 0.5. An LIR value of 0.3 is a good trade-off between

efficiency and load transient response. Increasing the LIR value results in more inductor ripple current, and speeds up the transient load

response. Decreasing the LIR value results in lower inductor ripple current and slows down the transient load response. The peak current

through the inductor should be considered when selecting the inductor. In particular, chose an inductor saturation current rating large

enough to handle the expected current. Allowing the inductor core to saturate reduces the overall converter efficiency, and raises the

temperature of both the inductor and the switching MOSFETs.

The inductor’s peak operating current is calculated as follows:

L = (5.0 V – 3.6 V) x (3.6 V/5.0 V) x (1/1.5 MHz) x (1/(0.3x2 A)) = 1.12

H.

Select the inductor to a standard 1.0

H.

Then calculate the total ripple current with a 1.0

H inductor:

The peak current on the inductor is 2.3 A.

Therefore, select an inductor that has a higher rated current than the peak current and 1.0

H.

Another consideration is the inductor DC resistance, since it directly affects the efficiency of the converter. Ideally, the inductor with the

lower DC resistance should be considered to achieve higher efficiency.

Table 5. Recommended Inductors

Part Number

Inductance (

H)

Size

DCR (m

Application

Vendor

CIGT2016201610GM1R0MNE

1.0

2.05 x1.65 x 0.9 mm

67

2300

2A charge

SEMCO

CIG22E1R0MNE

1.0

2.5 x2.0 x 1.0 mm

48

2300

2A charge

SEMCO

LQH32PN1R0-NN0

1.0

3.2 x 2.5 x 1.55 mm

54

2300

2A charge

Murata

1269AS-H-1R0M=P2

1.0

2.5 x 2 x 1.0 mm

60

3000

2A charge

TOKO

IFSC1008ABER1R0M01

1.0

2.5 x 2.0 x 1.2 mm

43

2600

2A charge

Vishay

CIG2MW1R0MNE

1.0

2.0 x 1.6 mm

85

1400

1A Charge

SEMCO

1285AS-H-1R0N=P2

1.0

2 x 1.6 x 1.0 mm

80

2300

1A Charge

TOKO

–



----------------------------

1

---------

1



-----------------------------------------







=

I



inductor

2

---------------------------------



where



=

I



inductor



=

I



inductor



0.3 2.0A



0.6A

==

=