AN3303

SRK2000 main characteristics

Doc ID 18164 Rev 2

5/27

1

SRK2000 main characteristics

The main features of the SRK2000 are described below. The values of the following

The SRK2000 implements a control scheme specific for secondary-side synchronous

rectification in an LLC resonant converter that uses a transformer with center-tap secondary

winding for full-wave rectification. It provides two high-current gate-drive outputs, each

capable of driving one or more N-channel power MOSFETs in parallel. Each gate driver is

controlled separately and an interlocking logic circuit prevents the two synchronous rectifier

MOSFETs from conducting simultaneously.

Figure 2.

Block diagram of an LLC converter with synchronous rectification

1.1

Drain MOSFET sensing and driving logic

The core function of the IC is to switch on each synchronous rectifier MOSFET whenever

the corresponding transformer half-winding starts conducting (i.e. when the MOSFET body

diode starts conducting) and then to switch it off when the flowing current approaches zero.

For this purpose, the IC is provided with two pins (DVS1 and DVS2) able to sense the power

MOSFET drain voltage level. Because each power MOSFET is turned on when its body

diode is conducting, zero voltage turn-on is achieved.

Device operations described below refer to Figure 3.

a)

When the current ISR1 starts flowing through the body diode, the voltage across

the power MOSFET drain-source becomes negative; as it reaches the negative

The threshold at which the power MOSFET turns on can be set by the following

formula:

Equation 1

V

THON

R

D

I

DVS1 2ON

,

V

DVS1 2TH

,

+

⋅

=

_