SRK2000 main characteristics

AN3303

6/27

Doc ID 18164 Rev 2

This may enable the ON threshold to be set according to the SR power MOSFET

parallel to the power MOSFET drain-source (e.g. Schottky rectifier).

The current sourcing out of the DVS1,2 pin is enabled after the drain-source

going edge) and is disabled once the rectifier is switched on. A de-bouncing delay

false triggering of the gate driver.

into the DVS pins when the corresponding SR power MOSFET is off. In fact, when

one power MOSFET is off (and the other is conducting) its drain-to-source voltage

is slightly higher than twice the output voltage; if this exceeds the voltage rating of

the internal clamp (VccZ = 36 V typ.), RD1,2 has to limit the injected current below

the maximum rating (25 mA). In addition, the SRK2000 clamping circuit dissipation

must be taken into account to avoid device overheating. In this case, Equation 1 is

SR power MOSFET body diode (or the parallel external diode).

b)

Once the power MOSFET is turned on, its drain-source voltage drops to:

Equation 2

which is negative because current flows from source to drain. When this voltage

switched off. The user can set the turn-off threshold selecting between two

startup phase.

c)

After the power MOSFET is switched off, the current still flows through its body

diode (causing the drain-source voltage to jump negative) until it becomes zero;

then the transformer winding voltage reverses and the drain-source voltage starts

increasing. As it exceeds the arming voltage VDVS1,2_A (positive going edge),

the gate drive of the second power MOSFET is armed and the operation,

described above, now applies to this rectifier.

V

DS1 2

,

R

DS on

,

⋅

=