TEA1791AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
Product data sheet Rev. 01 — 7 June 2010 4 of 13
NXP Semiconductors
TEA1791AT
GreenChip synchronous rectifier controller
If the secondary stroke of the flyback converter is shorter than 0.93 μs (typical), the driver
output is disabled. This will guarantee stable operation for very low duty cycles. When the
secondary stroke increases above 0.99 μs (typical), the driver output is again enabled.
7.4 Supply management
All internal reference voltages are derived from a temperature compensated, on-chip
band gap circuit.
7.5 Driver
The driver circuit to the gate of the external power MOSFET has a typical source
capability of 250 mA and a typical sink capability of 2.7 A. This permits fast turn-on and
turn-off of the power MOSFET for efficient operation. The source stage is coupled to the
timer (see Figure 1
). When the timer has finished, the source capability is reduced to a
small current (typical 5 mA) capable of keeping the driver output voltage at its level.
Typically, the time the driver source stage delivers the 250 mA is 100 ns shorter than the
minimum synchronous rectification active time (t
act(sr)(min)
).The output voltage of the driver
is limited to 10 V (typical). This high output voltage will drive all MOSFET brands to the
minimum on-state resistance.
During start-up conditions (V
CC
<V
startup
) and undervoltage lockout the driver output
voltage is actively pulled low.
Fig 3. Synchronous rectification signals
0 V
−12 mV
−55 mV
−310 mV
0 A
0 A
0 V
V
SRSENSE
V
DRIVER
Primary
current
Secondary
current