2ED2181S06F datasheet(12/24 Pages) INFINEON

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2020-07-07

2ED2181 (4) S06F (J)

650 V high-side and low-side driver with integrated bootstrap diode

The low ohmic current limiting resistor provides essential advantages over other competitor devices with high

ohmic bootstrap structures. A low ohmic resistor such as in the 2ED218x family allows faster recharching of the

bootstrap capacitor during periods of small duty cycles on the low side transistor. The bootstrap diode is usable

for all kind power electronic converters. The bootstrap diode is a real pn-diode and is temperature robust. It can

be used at high temperatures with a low duty cycle of the low side transistor.

The bootstrap diode of the 2ED218x family works with all control algorithms of modern power electronics, such

as trapezoidal or sinusoidal motor drives control.

5.7

Calculating the bootstrap capacitance CBS

Bootstrapping is a common method of pumping charges from a low potential to a higher one. With this technique

a supply voltage for the floating high side sections of the gate drive can be easily established according to Figure

13. This method has the advantage of being simple and low cost but may force some limitations on duty-cycle

and on-time since they are limited by the requirement to refresh the charge in the bootstrap capacitor.Proper

capacitor choice can reduce drastically these limitations.

Figure 13

Half bridge bootstrap circuit in 2ED218x

When the low side MOSFET turns on, it will force the potential of pin VS to GND. The existing difference between

the voltage of the bootstrap capacitor VCBS and VCC results in a charging current IBS into the capacitor CBS. The

current IBS is a pulse current and therefore the ESR of the capacitor CBS must be very small in order to avoid losses

in the capacitor that result in lower lifetime of the capacitor. This pin is on high potential again after low side is

turned off and high side is conducting current. But now the bootstrap diode DBS blocks a reverse current, so that

the charges on the capacitor cannot flow back to the capacitor CVCC. The bootstrap diode DBS also takes over the

blocking voltage between pin VB and VCC. The voltage of the bootstrap capacitor can now supply the high side

gate drive sections. It is a general design rule for the location of bootstrap capacitors CBS, that they must be placed

as close as possible to the IC. Otherwise, parasitic resistors and inductances may lead to voltage spikes, which

may trigger the undervoltage lockout threshold of the individual high side driver section.

The current limiting resistor RBS according to Figure 13 reduces the peak of the pulse current during the low side

MOSFET turn-on. The pulse current will occur at each turn-on of the low side MOSFET, so that with increasing

switching frequency the capacitor CBS is charged more frequently. Therefore a smaller capacitor is suitable at

higher switching frequencies. The bootstrap capacitor is mainly discharged by two effects: The high side

quiescent current and the gate charge of the high side MOSFET to be turned on.

The minimum size of the bootstrap capacitor is given by

2ED2181S06F Datasheet(PDF) 12 Page - Infineon Technologies AG