LP3913 Datasheet, PDF (57/70 Pages) Texas Instruments – Power Management IC for Flash Memory-Based Portable Media Players

LP3913
www.ti.com
SNVS489I – NOVEMBER 2006 – REVISED SEPTEMBER 2013
APPLICATIONS INFORMATION
Component Selection
Inductors for BUCK1, BUCK2 and BUCK3
There are two main considerations when choosing an inductor; the inductor should not saturate and the inductor
current ripple is small enough to achieve the desired output voltage ripple. Care should be taken when reviewing
the different saturation current ratings that are specified by different manufacturers.
Saturation current ratings are typically specified at 25ºC, so ratings at maximum ambient temperature of the
application should be requested from the manufacturer.
There are two methods to choose the inductor saturation current rating:
Method 1:The saturation current is greater than the sum of the maximum load current and the worst case
average to peak inductor current. This can be written as follows:
I_sat > I_outmax + I_ripple
1 ^Vin ^{- V}out
V_out
where I_ripple = _{f *}
2L
* _Vin
I_RIPPLE:
I_OUTMAX:
V_IN:
L:
f:
V_OUT:
Average to peak inductor current
Maximum load current
Maximum input voltage to the buck
Min inductor value including worse case tolerances (30% drop can be considered for method
1)
Minimum switching frequency (1.6 mHz)
Buck Output voltage
Method 2:A more conservative and recommended approach is to choose an inductor that has saturation current
rating greater than the maximum current limit of TBA.
Inductor
L_SW1,2
L_SW3
Value
2.2
2.2
Unit
Description
µH
BUCK1,2 Inductor
µH
BUCK3 Inductor
Notes
D.C.R. 70 mΩ
D.C.R. 70 mΩ
External Capacitors
The regulators on the LP3913 require external capacitors for regulator stability. These are specifically designed
for portable applications requiring minimum board space and smallest components. These capacitors must be
correctly selected for good performance.
LDO Capacitor Selection
Input Capacitor
An input capacitor is required for stability. It is recommended that a 1.0 µF capacitor be connected between the
LDO input pin and ground (this capacitance value may be increased without limit).
This capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean
analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.
Important: Tantalum capacitors can suffer catastrophic failures due to surge currents when connected to a low
impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input,
it must be specified by the manufacturer to have a surge current rating sufficient for the application.
There are no requirements for the ESR (Equivalent Series Resistance) on the input capacitor, but tolerance and
temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will remain
approximately 1.0 µF over the entire operating temperature range.
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
57
Product Folder Links: LP3913