BQ24153A_14 Datasheet, PDF (33/46 Pages) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger With Full USB Compliance and USB-OTG Support

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bq24153A, bq24156A
bq24158, bq24159
SLUSAB0C – OCTOBER 2010 – REVISED JULY 2013
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 allow the system to run off of the battery through 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 recommended if the system requires a high current.
2. Efficiency declines when discharging through the sense resistor to the system.
3. No thermal regulation. Therefore, the 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 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)
0.42
I_LPK = 1.25 + 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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