Datasheet

´
´ ´ D
OUT
L
VBAT (VBUS - VBAT)
L =
VBUS If
OUT
6
2.5 (5 - 2.5)
L =
5 (3 10 ) 1.25 0.3
´
´ ´ ´ ´
´
D
´ ´
L
OUT
VBAT (VBUS - VBAT)
I =
VBUS Lf
L
-6
2.5 (5 - 2.5)
I =
6
5 (3 10 ) (1 10 )
´
D
´ ´ ´ ´
L
LPK OUT
I
I I
2
D
= +
LPK
0.42
I 1.25
2
= +
OUT OUT
1
=
o
2 L C
f
p ´ ´
2 2
OUT
OUT
1
C
4 L
0
f
=
p ´ ´
2 3 2 -6
OUT
1
C
4 (40 10 ) (1 10 )
=
p ´ ´ ´ ´
(RSNS)
(SNS)
(CHARGE)
V
R
I
=
bq24155
www.ti.com SLUS942 –FEBRUARY 2010
, the worst case is when battery voltage is as close as to half of the input
voltage.
(4)
L
OUT
= 1.11 mH
Select the output inductor to standard 1 mH. Calculate the total ripple current with using the 1 mH inductor:
(5)
(6)
ΔI
L
= 0.42 A
Calculate the maximum output current:
(7)
(8)
I
LPK
= 1.46 A
Select 2.5mm by 2.0mm 1-mH 1.5-A surface mount multi-layer inductor. The suggested inductor part
numbers are shown as following.
Table 10. Inductor Part Numbers
PART NUMBER INDUCTANCE SIZE MANUFACTURER
LQM2HPN1R0MJ0 1 mH 2.5 x 2.0 mm muRata
MIPS2520D1R0 1 mH 2.5 x 2.0 mm FDK
MDT2520-CN1R0M 1 mH 2.5 x 2.0 mm TOKO
CP1008 1 mH 2.5 x 2.0 mm Inter-Technical
2. Determine the output capacitor value C
OUT
using 40 kHz as the resonant frequency:
(9)
(10)
(11)
C
OUT
= 15.8 mF
Select two 0603 X5R 6.3V 10-mF ceramic capacitors in parallel i.e., muRata GRM188R60J106M.
3. Determine the sense resistor using the following equation:
(12)
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.
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