TEA1795T Datasheet, PDF (8/14 Pages) NXP Semiconductors – GreenChip synchronous rectifier controller

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 kΩ. 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
V_in
Qprim1
PRIMARY
SIDE
CONTROLLER
CHB
TR
Qprim2
V_out
RDRNSENSE1
RDRNSENSE2
Cout
1 kΩ
Qsec1
IC1 ^VCC
DSA
DSB
1 kΩ
GDA _TEA1795T GDB
SSA
SSB
Qsec2
GND
001aal799
Fig 5. Typical resonant application with TEA1795T
TEA1795T
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 4 November 2010
© NXP B.V. 2010. All rights reserved.
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