bq24160, bq24161
bq24163, bq24168
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SLUSAO0A –NOVEMBER 2011–REVISED MARCH 2012
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 5 to calculate the peak current.
%
æ
ö
RIPPPLE
IPEAK = ILOAD(MAX)
´
1+
ç
÷
2
è
ø
(5)
The inductor selected must have a saturation current rating greater than or equal to the calculated IPEAK. Due to
the high currents possible with the bq2416x, a thermal analysis must also be done for the inductor. Many
inductors have a 40°C temperature-rise rating. The DC component of the current can 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 20% of the time, a Δ40°C temperature rise current must be greater than 1.7A:
ITEMPRISE = ILOAD + D ´
I
(
- ILOAD = 1.5A + 0.2 × 2.5A -1 .5A = 1.7A
(
)
)
PEAK
(6)
The bq2416x provides internal loop compensation. Using this scheme, the bq2416x is stable with 10µF to 200µF
of local capacitance on the SYS output. 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 capacitor is recommended for optimal transient response.
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