BQ24140_14 Datasheet, PDF (33/39 Pages) Texas Instruments – Integrated Dual-Input Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support

bq24140
www.ti.com
SLUSAO5 – OCTOBER 2011
DESIGN EXAMPLE FOR TYPICAL APPLICATION CIRCUIT
Systems Design Specifications:
• VBUS = 5 V
• V_BAT = 4.2 V (1-Cell)
• I_(charge) = 1.25 A
• Inductor ripple current = 30% of fast charge current
1. Determine the inductor value (L_OUT) for the specified charge current ripple:
L_OUT =
VBAT ´ (VBUS - VBAT)
VBUS ´ f ´ DI_L
, the worst case is when battery voltage is as close as to half of the input
voltage.
L_OUT
=
5
´
2.5 ´ (5 - 2.5)
(3 ´ 10⁶ ) ´ 1.25
´
0.3
(4)
L_OUT = 1.11 μH
Select the output inductor to standard 1 μH. Calculate the total ripple current with using the 1-μH inductor:
DI_L
=
VBAT ´ (VBUS - VBAT)
VBUS ´ f ´ L_OUT
(5)
DI_L
=
5
´
2.5 ´ (5 -
(3 ´ 106 ) ´
2.5)
(1 ´
10^-6 )
(6)
ΔI_L = 0.42 A
Calculate the maximum output current:
I_LPK
= I_OUT
+
DI_L
2
(7)
I_LPK
= 1.25 +
0.42
2
(8)
I_LPK = 1.46 A
Select 2.5mm by 2mm 1-μH 1.5-A surface mount multi-layer inductor. The suggested inductor part numbers
are shown as following.
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