BQ24165_14 Datasheet, PDF (25/38 Pages) Texas Instruments – 2.5A, Dual-Input, Single Cell Switch Mode Li-Ion Battery Charger with Power Path Management

www.ti.com
bq24165
bq24166
bq24167
SLUSAP4B – DECEMBER 2011 – REVISED MARCH 2013
APPLICATION INFORMATION
OUTPUT INDUCTOR AND CAPACITOR SELECTION GUIDELINES
When selecting an inductor, several attributes must be examined to find the right part for the application. First,
the inductance value should be selected. The bq2416x is designed to work with 1.5µH to 2.2µH inductors. The
chosen value will have an effect on efficiency and package size. Due to the smaller current ripple, some
efficiency gain is reached using the 2.2µH inductor, however, due to the physical size of the inductor, this may
not be a viable option. The 1.5µH inductor provides a good tradeoff between size and efficiency.
Once the inductance has been selected, the peak current must be calculated in order to choose the current
rating of the inductor. Use Equation 8 to calculate the peak current.
I_{PEA K}
= I_LOAD(MAX)
´
æ
çè^{1 +}
%_{RIP PPLE}
2
ö
÷ø
(8)
The inductor selected must have a saturation current rating higher than the calculated I_PEAK. Due to the high
currents possible with the bq2416x, a thermal analysis must also be done for the inductor. Many inductors have
40°C temperature rise rating. This is the DC current that will cause a 40°C temperature rise above the ambient
temperature in the inductor. For this analysis, the typical load current may be used adjusted for the duty cycle of
the load transients. For example, if the application requires a 1.5A DC load with peaks at 2.5A for 20% of the
time, a Δ40°C temperature rise current must be greater than 1.7A:
I_TEMPRISE = I_LOAD + D × (I_PEAK – I_LOAD) = 1.5 A + 0.2 × (2.5 A – 1.5 A) = 1.7 A
The bq2416x provides internal loop compensation. Using this scheme, the bq2416x is stable with 10µF to 200µF
of local capacitance. The capacitance on the SYS rail can be higher if distributed amongst the rail. To reduce the
output voltage ripple, a ceramic capacitor with the capacitance between 10µF and 47µF is recommended for
local bypass to SYS. A 47µF bypass capacitance on SYS is recommended to optimize the transient response.
PCB LAYOUT GUIDELINES
It is important to pay special attention to the PCB layout. Figure 26 provides a sample layout for the high current
paths of the bq2416x.
IN ^PMIDI
SW
PGND
ILIM
SYS
BAT
PMIDU
USB
PGND
BOOT
ISET
USB
PGND
PMIDU
VDPM
IN
PGND ^BOOT
PMIDI
ISET
ILIM
SYS
SW
SYS
BAT
WCSP Layout
QFN Layout
Figure 26. Recommended bq2416x PCB Layout
Copyright © 2011–2013, Texas Instruments Incorporated
Submit Documentation Feedback
25
Product Folder Links: bq24165 bq24166 bq24167