tea1791t/n1 NXP Semiconductors, tea1791t/n1 Datasheet - Page 3

• Manufacturer Part Number: tea1791t/n1
• Description: Greenchip Synchronous Recti?er Controller
• Manufacturer: NXP Semiconductors

NXP Semiconductors
7. Functional description
TEA1791T_1
Product data sheet
7.1 Introduction
7.2 Start-up and UnderVoltage LockOut (UVLO)
7.3 Synchronous rectification
The TEA1791T is the controller for synchronous rectification to be used in discontinuous
conduction mode and quasi-resonant flyback converters.
The IC leaves the undervoltage lockout state and activates the synchronous rectifier
circuitry as soon as the voltage on the V
drops below 8.0 V (typ), the undervoltage lockout state is reentered and the SR driver
output is actively kept low.
After a negative voltage ( 310 mV typ) is sensed on the SRSENSE pin, the driver output
voltage is driven HIGH and the external MOSFET is switched on. As soon as the
SRSENSE voltage rises to 55 mV the driver output voltage is regulated to maintain the
driver output is pulled to ground.
After switch-on of the SR MOSFET, the input signal on the SRSENSE pin is blanked for
2 s (typ). This eliminates false switch-off due to high frequency ringing at the start of the
secondary stroke.
Because the driver output voltage is reduced as soon as the voltage on the SRSENSE pin
is 55 mV, the external power switch can be switched off quickly when the current through
the switch reaches zero. With this zero current switch-off, no separate standby mode is
needed to maintain high efficiency during the no-load operation. The zero current is
detected by sensing a 12 mV level on the SRSENSE pin (see
55 mV on the SRSENSE pin. As soon as the SRSENSE voltage is above 12 mV, the
Rev. 01 — 3 February 2009
CC
pin is above 8.5 V (typ). As soon as the voltage
GreenChip synchronous rectifier controller
Figure
TEA1791T
3).
© NXP B.V. 2009. All rights reserved.
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