TLE6361G Datasheet, PDF (52/57 Pages) Infineon Technologies AG – Multi-Voltage Processor Power Supply

TLE 6361 G
5.2.5 Bootstrap capacitor (C_BTP)
The voltage at the Bootstrap capacitor does not exceed 15V, a ceramic type with a
minimum of 2% of the buck output capacitance and voltage class 16V would be
sufficient.
5.2.6 External charge pump capacitors (C_FLY, C_CCP)
Out of the feedback voltage the charge pump generates a voltage between 8 and 10V.
The fly capacitor connected between C+ and C- is charged with the feedback voltage
level and discharged to achieve the (almost) double voltage level at CCP. C_FLY is chosen
to 100nF and C_CCP to 220nF, both ceramic types.
The connection of CCP to a voltage source of e.g. 7V (take care of the maximum
ratings!) via a diode improves the start-up behavior at very low battery voltage. The diode
with the cathode on CCP has to be used in order to avoid any influence of the voltage
source to the device’s operation and vice versa.
5.2.7 Input filter components for reduced EME (C_I1, C_I2, C_I3, L_I, R_Slew)
At the input of Buck converters a square wave current is observed causing
electromagnetical interference on the battery line. The emission to the battery line
consists on one hand of components of the switching frequency (fundamental wave) and
its harmonics and on the other hand of the high frequency components derived from the
current slope. For proper attenuation of those interferers a π-type input filter structure is
recommended which is built up with inductive (L_I) and capacitive components (C_I1, C_I2,
C_I3). The inductance can be chosen up to the value of the Buck converter inductance,
higher values might not be necessary, C_I1 and C_I3 should be ceramic types and for C_I2 an
input capacitance with very low ESR should be chosen and placed as close to the input
of the Buck converter as possible.
Inexpensive input filters show due to their parasitrics a notch filter characteristic, which
means basically that the lowpass filter acts from a certain frequency as a highpass filter
and means further that the high frequency components are not attenuated properly. For
that reason the TLE 6361 G offers the possibility of current slope adjustment. The current
transistion time can be set by the external slew resistor to times between 20ns and 80ns
by varying the resistor value bewteen 0Ω (fastest transition) and 20kΩ (slowest
transistion).
5.2.8 Feedback circuit for minimum switching loss (R_Boost, C_Boost, D_Boost)
To decrease the switching losses to a mininum the external components R_Boost, C_Boost
and D_Boost are needed. The current through the feedback resistor R_Boost is about a few
mA where the Diode D_Boost and the capacitor C_Boost run a part of the load current.
If this feature is not needed the three components are not needed and the Boost pin (33)
can be connected directly to the IN pins(32, 30).
Data Sheet, Rev. 1.31
52
2004-10-12