UM10892 Datasheet, PDF (7/16 Pages) NXP Semiconductors – GreenChip TEA1995DB1295 synchronous rectifier controller demo board

NXP Semiconductors
UM10892
TEA1995DB1295 synchronous rectifier controller demo board
6. Operation
6.1 Turn-on
The MOSFETs are turned on when the drain-source voltage drops to below the turn-on
threshold (400 mV). The corresponding gate driver output turns on the external SR
MOSFET. The gate of this MOSFET is rapidly charged to a level that exceeds its
threshold level. After the turn-on phase, the regulation phase starts. There is no minimum
on-time.
6.2 Regulation mode and turn-off
During regulation mode, the IC regulates the voltage difference between the drain and the
source sense inputs to an absolute level of 55 mV. The corresponding gate driver output
level is adjusted accordingly. In this mode, the gate driver voltage follows the waveform of
the current through the external MOSFET. When the current drops to lower values, the
corresponding gate driver output is discharged to a value just above the gate-source
threshold level of the external MOSFET. The discharge enables a quick turn-off of the
external MOSFET when the current reaches zero.
Especially at Continuous Conduction Mode (CCM) conditions, it is important to choose a
MOSFET with a sufficiently low R_DSon value. It enables the discharge of the gate driver
output to just above the gate-source threshold level of the external MOSFET. When the
current drops to zero, this discharge makes a rapid switch-off possible. The rapid
switch-off is very important for CCM conditions. It minimizes the reverse current and the
related voltage overshoot on the drain terminal of the external MOSFET.
When the drain voltage exceeds 150 mV, the driver output voltage is actively pulled low.
UM10892
User manual
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 8 July 2015
© NXP Semiconductors N.V. 2015. All rights reserved.
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