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BQ24150 Datasheet, PDF (32/39 Pages) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support
◁
bq24150
bq24151
SLUS824 – JUNE 2008 ...................................................................................................................................................................................................... www.ti.com
2. Determine the output capacitor value COUT using 40 kHz as the resonant frequency:
1
fo =
2p ´ LOUT ´ COUT
1
COUT = 4p2 ´ f02 ´ LOUT
COUT
=
1
4p2 ´ (40 ´ 103 )2 ´ (1 ´ 10-6 )
COUT = 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 85mV, 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.
Battery Charge Efficiency
90
TA=25°C,
89
TOKO
VBUS = 5 V,
88
FDK VBAT = 3 V
87
muRata
86
Inter-Technical
85
84
83
82
500 600 700 800 900 1000 1100 1200 1300
Charge Current - mA
Battery Charge Loss
800
TA=25°C,
700 VBUS = 5 V,
VBAT = 3 V
600
500
Inter-Technical
400
muRata
TOKO
FDK
300
200
100
500 600 700 800 900 1000 1100 1200 1300
Charge Current - mA
Figure 34. Measured Efficiency and Power Loss
32
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