BQ24153 Datasheet, PDF (33/40 Pages) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger With Full USB Compliance and USB-OTG Support

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bq24153
bq24156, bq24158
SLUSA27 – MARCH 2010
3. The charger can disable termination and keep the converter running to keep battery fully charged, or let the
switcher terminate when the battery is full and then run off of the battery via the sense resistor.
Design considerations and potential issues:
1. The total current is limited by the IC input current limit, or peak current protection, but not the charge current
setting. The charge current does not drop when the system current load increases until the input current limit
is reached. This solution is not applicable if the system requires a high current.
2. Efficiency declines when discharging through the sense resistor to the system.
3. No thermal regulation. Therefore, system design should ensure the maximum junction temperature of the IC
is below 125°C during normal operation.
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 mH
Select the output inductor to standard 1 mH. Calculate the total ripple current with using the 1-mH 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)
0.42
I_LPK = 1.25 + ₂
(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.
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