Data Sheet TLE6284G

Data Sheet

10

Rev 2.4 2008-03-18

Operation at different voltages for Vs, DH1 and DH2

If DH1 and DH2 are used with a voltage higher than Vs, a duty cycle of 100% can not be

guaranteed. In this case the driver is acting like a normal driver IC based on the bootstrap

principle. This means that after a maximum “On” time of the highside switch of more than

1ms a refresh pulse to charge the bootstrap capacitor of about 1µs is needed to avoid un-

dervoltage lock out of this output stage.

Operation at extreme duty cycle:

The integrated charge pump allows an operation at 100% duty cycle. The charge pump is

strong enough to replace leakage currents during “on”-phase of the highside switch. The

gate charge for fast switching of the highside switches is supplied by the bootstrap capaci-

tors. This means, that the bootstrap capacitor needs a minimum charging time of about 1µs,

if the highside switch is operated in PWM mode (e.g. with 20kHz a maximum duty cycle of

96% can be reached). The exact value for the upper limit is given by the RC time formed by

the impedance of the internal bootstrap diode and the capacitor formed by the external Mos-

MOSFET the driver IC has to drive. Usually the bootstrap capacitor is about 10-20 times big-

The charge pump is active when the highside switch is “ON” and the voltage level at the SHx

is higher than 4V. Only under these conditions the bootstrap capacitor is charged by the

charge pump.