FN6439 Rev 6.00

Page 8 of 9

July 19, 2012

ISL97656

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Cascaded MOSFET Application

A 24V N-Channel MOSFET is integrated in the boost regulator. For

the applications where the output voltage is greater than 24V, an

external cascaded MOSFET is needed as shown in Figure 16. The

voltage rating of the external MOSFET should be greater than

VIN.

DC PATH BLOCK APPLICATION

There is a DC path in the boost converter from the input to the

output through the inductor and diode. In the non-synchronous

topology, although the system is still in shutdown mode, the

output voltage will be the input voltage minus the forward

voltage diode drop of the Schottky diode. If this voltage is not

desired, the following circuit (see Figure 17) can be used between

input and inductor to disconnect the DC path when the ISL97656

is in shutdown mode.

FIGURE 16. CASCADED MOSFET TOPOLOGY FOR HIGH OUTPUT

VOLTAGE APPLICATIONS

INTERSIL

ISL97656

LX

FB

VOUT

VIN

FIGURE 17. CIRCUIT TO DISCONNECT THE DC PATH OF BOOST

CONVERTER

INPUT

EN

TO INDUCTOR