ISL6527, ISL6527A

FN9056 Rev 11.00

Page 13 of 17

Sep 29, 2015

the equivalent gate-source capacitance of the upper MOSFET

as shown in Equation 19:

the bootstrap voltage immediately after turn-on.

The bootstrap capacitor begins its refresh cycle when the gate

drive begins to turn-off the upper MOSFET. A refresh cycle ends

when the upper MOSFET is turned on again, which varies

depending on the switching frequency and duty cycle.

The minimum bootstrap capacitance can be calculated by

rearranging Equation 19 and solving for CBOOT in

Equation 20.

Typical gate charge values for MOSFETs considered in these

types of applications range from 20 to 100nC. Since the

the voltage drop across the bootstrap capacitor during the on-

less than 4V will quickly help narrow the bootstrap capacitor

range.

For example, consider an upper MOSFET is chosen with a

across the bootstrap capacitor to 1V results in a value of no

less than 0.1µF. The tolerance of the ceramic capacitor should

also be considered when selecting the final bootstrap

capacitance value.

A fast recovery diode is recommended when selecting a

bootstrap diode to reduce the impact of reverse recovery

to be added to the gate charge of the MOSFET and taken into

consideration when calculating the minimum bootstrap

capacitance.

ISL6527, ISL6527A DC/DC Converter

Application Circuit

Figure 8 shows an application circuit of a DC/DC Converter.

Detailed information on the circuit, including a complete Bill-of-

Materials and circuit board description, can be found in

Application Note AN1021.

http://www.intersil.com/data/an/an1021.pdf

ISL6527,

GND

LGATE

UGATE

PHASE

BOOT

VIN

NOTE:

NOTE:

CBOOT

DBOOT

+

-

FIGURE 7. UPPER GATE DRIVE BOOTSTRAP

+

-

CPVOUT

ISL6527A

–





=

(EQ. 19)

–

BOOT2

-----------------------------------------------------



(EQ. 20)