BQ24152 Datasheet, PDF (31/38 Pages) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support

bq24152
www.ti.com ...................................................................................................................................................................................................... SLUS847 – JUNE 2008
I_LPK
= I_OUT
+
DI_L
2
0.42
I_LPK = 1.25 + ₂
I_LPK = 1.46 A
Select 2.5mm by 2.0mm 1-µH 1.5-A surface mount multi-layer inductor. The suggested inductor part
numbers are shown as following.
PART NUMBER
LQM2HPN1R0MJ0
MIPS2520D1R0
MDT2520-CN1R0M
CP1008
Table 12. Inductor Part Numbers
INDUCTANCE
1 µH
1 µH
1 µH
1 µH
SIZE
2.5 x 2.0 mm
2.5 x 2.0 mm
2.5 x 2.0 mm
2.5 x 2.0 mm
MANUFACTURER
muRata
FDK
TOKO
Inter-Technical
2. Determine the output capacitor value C_OUT using 40 kHz as the resonant frequency:
1
f_o =
2p ´ L_OUT ´ C_OUT
1
C_OUT = _{4p2 ´ f02 ´ LOUT}
C_OUT
=
1
4p² ´ (40 ´ 10³ )² ´ (1 ´ 10^-6 )
C_OUT = 15.8 µF
Select two 0603 X5R 6.3V 10-µF ceramic capacitors in parallel i.e., muRata GRM188R60J106M.
3. Determine the sense resistor using the following equation:
R_(SNS)
=
V_(RSNS)
I_(CHARGE)
The maximum sense voltage across sense resistor is 85 mV. In order to get a better current regulation
accuracy, V_(RSNS) should equal 85 mV, and calculate the value for the sense resistor.
R_(SNS)
=
85mV
1.25A
R_(SNS) = 68 mΩ
This is a standard value. If it is not a standard value, then choose the next close value and calculate the real
charge current. Calculate the power dissipation on the sense resistor:
P_(RSNS) = I_(CHARGE)2 × R_(SNS)
P_(RSNS) = 125² × 0.068
P_(RSNS) = 0.106 W
Select 0402 0.125-W 68-mΩ 2% sense resistor, i.e. Panasonic ERJ2BWGR068.
4. Measured efficiency and total power loss for different inductors are shown in Figure 34.
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