MPZ2012S221A datasheet(42/56 Pages) STMICROELECTRONICS

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Figure 48. RC snubber network

VIN

VINLDO

EN/CLKIN

FSW

VCC

AGND

PGOOD

BOOT

VBIAS

PGND

VIN

GND

VOUT_prim

VOUT_iso

GND_iso

L6983I

CIN

CLDO

RLDO

RFSW1

CVCC

RFB1

RFB2

CSEC

COUT

snubber network

Capacitance

The parasitic capacitance of a real transformer mainly consists of the following contributions:

•

Capacitance across each winding (CP and CS, in the image below) due to the capacitive coupling between

the coil and the core. As already mentioned, the winding capacitances are involved in the ringing observed

during transition from off to on-phase of the primary side.

•

Interwinding capacitance (CWW), that is the capacitance between windings. The interwinding capacitance

should be reduced in order to limit disturbance on the primary side due to possible steep voltage transitions

present in the load connected to the secondary output.

Figure 49. Transformer parasitic capacitances

10.3

Schottky diode

In the selection of the Schottky diode, the following parameters should be considered:

•

Maximum forward current, mainly defined by the secondary output current demand (see Eq. (44))

•

Forward voltage drop, which affects the secondary output voltage regulation

•

Maximum peak reverse voltage. During the on-phase of the primary side, when in the secondary side no

current flows, the diode is reverse biased and must withstand this voltage:

VD1_rev=N∙VINmax−VOUT_pri+VOUT_sec

(45)

•

Junction capacitance, which should be as low as possible in order to reduce the ringing described in the

previous section

L6983I

Schottky diode

DS14040 - Rev 1

page 42/56

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