BC3770 Datasheet, PDF (38/45 Pages) Freescale Semiconductor, Inc – 2.0 A Switch-Mode Charger

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.
L = VBUS_MAX – VSYS_MIN  _{V--V---B-S----UY----S-S---MM}----_A-^I--^N-_X--  -f--_S-1--_W--  _{L-----I--R-----}-----I--_O-1---_U----_T---_M-----_A---_X--
Where f_SW is the switching frequency and LIR is the inductor current ration expressed as a percentage of I_OUT (e.g., for a 300 mA ripple
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:
I_PEAK = IOUT_MAX  ^---^----I--^--i--n---2-d---u----c---t--o---r where
Iinductor = LIR  I_OUTMAX
For instance, VBUS = 5.0 V, VSYS = 4.0 V, I_OUT = 2.0 A, f_SW = 1.5 MHz
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:
Iinductor = LIR  I_OUTMAX = 0.3  2.0A = 0.6A
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)
CIGT2016201610GM1R0MNE
1.0
CIG22E1R0MNE
1.0
LQH32PN1R0-NN0
1.0
1269AS-H-1R0M=P2
1.0
IFSC1008ABER1R0M01
1.0
CIG2MW1R0MNE
1.0
1285AS-H-1R0N=P2
1.0
Size
2.05 x1.65 x 0.9 mm
2.5 x2.0 x 1.0 mm
3.2 x 2.5 x 1.55 mm
2.5 x 2 x 1.0 mm
2.5 x 2.0 x 1.2 mm
2.0 x 1.6 mm
2 x 1.6 x 1.0 mm
DCR (m)
Rated Current (mA)
T = 40 °C
Application
67
2300
2A charge
48
2300
2A charge
54
2300
2A charge
60
3000
2A charge
43
2600
2A charge
85
1400
1A Charge
80
2300
1A Charge
Vendor
SEMCO
SEMCO
Murata
TOKO
Vishay
SEMCO
TOKO
Analog Integrated Circuit Device Data
Freescale Semiconductor
BC3770
38