TLE6368 datasheet(53/59 Pages) INFINEON

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TLE 6368 / SONIC

Data Sheet

Rev. 2.2, 2006-12-01

5.2.5

Bootstrap capacitor (CBTP)

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 (CFLY, CCCP)

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. CFLY is chosen

to 100nF and CCCP 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 (CI1, CI2, CI3, LI, RSlew)

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 (LI) and capacitive components (CI1, CI2,

CI3). The inductance can be chosen up to the value of the Buck converter inductance,

higher values might not be necessary, CI1 and CI3 should be ceramic types and for CI2 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 parasitics 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 6368 G1 / SONIC offers the possibility of current slope adjustment.

The current transition time can be set by the external resistor (located on the SLEW pin)

to times between 20ns and 80ns by varying the resistor value between 0

Ω (fastest

transition) and 20k

Ω (slowest transition).

5.2.8

Feedback circuit for minimum switching loss (RBoost, CBoost, DBoost)

To decrease the switching losses to a minimum the external components RBoost, CBoost

and DBoost are needed. The current though the feedback resistor RBoost is about a few mA

where the Diode DBoost and the capacitor CBoost 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).

TLE6368 Datasheet(PDF) 53 Page - Infineon Technologies AG

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