LM3279_16 Datasheet, PDF (23/37 Pages) Texas Instruments – Buck-Boost Converter

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LM3279
SNVS970C – MARCH 2013 – REVISED OCTOBER 2014
If a smaller inductance inductor is used in the application, the VOUT transient response time is affected. If a
winding type inductor is used, the efficiency at light load current condition may not be so good due to bigger
DCR.
8.2.1.2.2.2 Input Capacitor Selection
A ceramic input capacitor of 10 µF, 6.3V, 0402 or higher is sufficient for most applications. Place the input
capacitor as close as possible to the PVIN pin and PGND pin of the device. A larger value of higher voltage
rating may be used to improve input filtering. Use X7R, X5R, or B types; do not use Y5V or F. The input filter
capacitor supplies current to the PFET (high-side) switch in the first half of each cycle and reduces voltage ripple
imposed on the input power source. A ceramic capacitor’s low ESR provides the best noise filtering of the input
voltage spikes due to this rapidly changing current.
8.2.1.2.3 Output Capacitor Selection
Use a 10-µF, 6.3-V, 0402 capacitor for the output capacitor. Use of capacitor types such as X5R, X7R is
recommended for the filter. These provide an optimal balance between small size, cost, reliability, and
performance for cell phones and similar applications. Table 4 lists suggested part numbers and suppliers. DC
bias characteristics of the capacitors must be considered while selecting the voltage rating and case size of the
capacitor. Smaller case sizes for the output capacitor mitigate piezo-electric vibrations of the capacitor when the
output voltage is stepped up and down at fast rates. However, they have a bigger percentage drop in value with
DC bias. A 0402 case size output capacitor is recommended for small solution size. For RF Power Amplifier
applications, the output capacitor loading is combined between the DC-DC converter and the RF Power
Amplifier(s). (10 μF (0402) + PA input cap 3 x 1μF (0402/0201) is recommended.) The optimum capacitance split
is application-dependent. Place all the output capacitors very close to their respective device. If using a 4.7 μF,
0402 as the output capacitor, the total recommended actual capacitance on the VOUT bus should be at least >
6.8 μF (4.7 μF + PA decoupling caps), to take into account the 0402 DC bias degradation and other tolerances.
The minimum capacitance under DC bias conditions should be > 3 μF.
Table 4. Suggested Capacitors
MODEL
10 µF for C_IN = C_OUT
CL05A106MQ5NUN (0402)
1.0 µF for PA Decoupling Caps (x 3)
C0603X5R0G105M(0201(0603))
0.47 µF for PA Decoupling Caps (x 2)
GRM033R60J474ME90 (0201(0603))
VENDOR
Samsung
TDK
Murata
8.2.1.3 Application Curves
V_OUT = 3.5 V
PVIN = 3.8 V
V_OUT = 0.8 V
PVIN = 4.2 V
Figure 25. Load Transient, Forced PWM Mode
Figure 26. Load Transient, Forced PFM Mode
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