TLE6389_07 datasheet(34/38 Pages) INFINEON

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TLE 6389

Datasheet Rev. 2.1

2007-08-13

7.10.6

Freewheeling diode / catch diode (D1)

For lowest power loss in the freewheeling path Schottky diodes are recommended. With

those types the reverse recovery charge is negligible and a fast hand over 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. Also for high

temperature operation select a Schottky-diode with low reverse leakage.

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.

7.10.7

Buck driver supply capacitor (CBDS)

The voltage at the ceramic capacitor is clamped internally to 7V, a ceramic type with a

minimum of 220nF and voltage class 16V would be sufficient.

7.10.8

Input pi-filter components for reduced EME

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 and capacitive components in addition to

the Input caps C

IN1 and CIN2. The inductance can be chosen up to the value of the Buck

converter inductance, higher values might not be necessary, the additional capacitance

should be a ceramic type in the range up to 100nF.

Inexpensive input filters show due to their parasitrics a notch filter characteristic, which

means basically that the low pass filter acts from a certain frequency as a high pass filter

and means further that the high frequency components are not attenuated properly. To

slower down the slopes at the gate of the PMOS switch and get down the emission in the

high frequency range a small gate resistor can be put between GDRV and the PMOS

gate.

7.10.9

Frequency compensation

The external frequency compensation pin should be connected via a 2.2nF (>10V)

ceramic capacitor and a 680

Ω (1/8W) resistor to GND. This node should be kept free

from switching noise.

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