TLE6368_06 Datasheet, PDF (52/59 Pages) Infineon Technologies AG – Multi-Voltage Processor Power Supply

TLE 6368 / SONIC
5.2.2 Buck output capacitor (C_B) selection:
The choice of the output capacitor effects straight to the minimum achievable ripple
which is seen at the output of the buck converter. In continuous conduction mode the
ripple of the output voltage equals:
V_Ripple = ∆I ⋅ _R_ESRCB + -8----_â‹---f--_S---_W^1------_â‹---C----_B--_
From the formula it is recognized that the ESR has a big influence in the total ripple at
the output, so ceramic types or low ESR tantalum capacitors are recommended for the
application.
One other important thing to note are the requirements for the resonant frequency of the
output LC-combination. The choice of the components L and C have to meet also the
specified range given in section 3.3 otherwise instabilities of the regulation loop might
occur.
5.2.3 Input capacitor (C_I2) selection:
At high load currents, where the current through the inductance flows continuously, the
input capacitor is exposed to a square wave current with its duty cycle V_OUT/V_I. To
prevent a high ripple to the battery line a capacitor with low ESR should be used. The
maximum RMS current which the capacitor has to withstand is calculated to:
I_RMS = I_LOAD ⋅
V-----_{O----U----T- â‹}
V_IN
1
+
1--
3
⋅


-2----_â‹---I-^∆-_L---I_O----_A----_D--_
2
5.2.4 Freewheeling diode / catch diode (D_B)
For lowest power loss in the freewheeling path Schottky diodes are recommended. With
those types the reverse recovery charge is negligible and a fast handover from
freewheeling to forward conduction mode is possible. Depending on the application (12V
battery systems) 40V types could be also used instead of the 60V diodes.
A fast recovery diode with recovery times in the range of 30ns can be also used if smaller
junction capacitance values (smaller spikes) are desired, the slew resistor should be set
in this case between 10 and 20kW.
Data Sheet
52
Rev. 2.2, 2006-12-01