TEA1795T

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© NXP B.V. 2010. All rights reserved.

Product data sheet

Rev. 1 — 4 November 2010

8 of 14

NXP Semiconductors

TEA1795T

GreenChip synchronous rectifier controller

11. Application information

A switched mode power supply with the TEA1795T consists of a primary side half bridge,

a transformer, a resonant capacitor and an output stage. In the output stage

SR MOSFETs are used to obtain low conduction loss rectification. These SR MOSFETs

are controlled by the TEA1795T.

The timing for the synchronous rectifier switch is derived from the voltage difference

between the corresponding drain sense and source sense pins. The resistor in the drain

sense connection is needed to protect the TEA1795T against excessive voltages. These

resistors should typically be 1 k

Ω. Higher values might impair correct timing, lower values

may not provide sufficient protection.

Special attention should be paid to the connection of the drain sense and source sense

pins. The voltages measured on these pins are used for the timing of the gate driver

output. Wrong measurement results in wrong timing. The connections to these pins

should not interfere with the power wiring. The power wiring conducts currents with high

dI/dt values. This can easily cause measurement errors resulting from induced voltages

due to parasitic inductances. The separate source sense pins make it possible to sense

the source voltage of the external MOSFETs directly, without having to use the current

carrying power ground tracks for this.

11.1 Application diagram resonant application

Fig 5.

Typical resonant application with TEA1795T

001aal799

DSA

GDA

SSA

DSB

GDB

SSB

GND

Qprim1

CHB

RDRNSENSE1

Qprim2

Qsec1

PRIMARY

SIDE

CONTROLLER

TEA1795T

TR

IC1

RDRNSENSE2

Qsec2

Cout

1 k

Ω

1 k

Ω