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TEA1791T
Synchronous rectification controller suitable for both high-side and low-side control
1. General description
The TEA1791T is a member of the new generation of Synchronous Rectifier (SR)
controller ICs for switched mode power supplies. Its high level of integration allows the
design of a cost-effective power supply with a very low number of external components.
The TEA1791T is a controller IC dedicated to synchronous rectification on the secondary
side of discontinuous conduction mode and quasi-resonant flyback converters.
The TEA1791T is fabricated in a Silicon On Insulator (SOI) process.
2. Features and benefits
2.1 Distinctive features Accurate synchronous rectification functionality Wide supply voltage range (8.5 V to 38V) High level of integration, resulting in a very low external component count High driver output voltage of 10 V to drive all MOSFET brands to the lowest RDSon
2.2 Green features Low current consumption High system efficiency from no load to full load
2.3 Protection features Undervoltage protection
3. Applications The TEA1791T is intended for adapters. The device can also be used in all other
discontinuous conduction mode systems and quasi-resonant flyback systems that
demand a highly efficient and cost-effective solution.
4. Ordering information
TEA1791T
GreenChip synchronous rectifier controller
Rev. 02 — 7 June 2010 Product data sheet
Table 1. Ordering information
TEA1791T/N1 SO8 plastic small outline package; 8 leads; body width 3.9 mm SOT96-1
NXP Semiconductors TEA1791T
GreenChip synchronous rectifier controller
5. Block diagram
6. Pinning information
6.1 Pinning
6.2 Pin description
Table 2. Pin description
SRSENSE 1 synchronous timing input
GND 2 ground
n.c. 3 not connected
DRIVER 4 driver output for SR MOSFET
n.c 5 not connected
n.c. 6 not connected
n.c. 7 not connected
VCC 8 supply voltage
NXP Semiconductors TEA1791T
GreenChip synchronous rectifier controller
7. Functional description
7.1 Introduction
The TEA1791T is the controller for synchronous rectification to be used in discontinuous
conduction mode and quasi-resonant flyback converters.
7.2 Start-up and UnderVoltage LockOut (UVLO)
The IC leaves the undervoltage lockout state and activates the synchronous rectifier
circuitry as soon as the voltage on the VCC pin is above 8.5 V (typical). When the voltage
drops below 8.0 V (typical), the undervoltage lockout state is reentered and the SR driver
output is actively kept low.
7.3 Synchronous rectification
After a negative voltage (−310 mV typical) 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 −55 mV on the SRSENSE pin. When the SRSENSE voltage is above −12 mV, the driver
output is pulled to ground.
After switch-on of the SR MOSFET, the input signal on the SRSENSE pin is blanked for μs (typical). This eliminates false switch-off due to high frequency ringing at the start of
the secondary stroke.
Because the driver output voltage is reduced when 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. The zero current switch-off removes the need for a separate
Standby mode 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 Figure3).
NXP Semiconductors TEA1791T
GreenChip synchronous rectifier controller
If the secondary stroke of the flyback converter is shorter than 2 μs (typical), the driver
output is disabled. This will guarantee stable operation for very low duty cycles. When the
secondary stroke increases above 2.2 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 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 (VCC voltage is actively pulled low.
NXP Semiconductors TEA1791T
GreenChip synchronous rectifier controller
8. Limiting values
[1] Equivalent to discharging a 100 pF capacitor through a 1.5 kΩ series resistor.
[2] Equivalent to discharging a 200 pF capacitor through a 0.75 μH coil and a 10 Ω series resistor.
9. Thermal characteristics
Table 3. Limiting values
In accordance with the Absolute Maximum Rating System (IEC 60134). All voltages are measured
with respect to ground (pin 2); positive currents flow into the chip. The voltage ratings and current
ratings are valid provided the other ratings are not violated.
Voltages
VCC supply voltage continuous −0.4 +38 V
VSRSENSE voltage on pin SRSENSE continuous - 120 V
Currents
IDRIVER current on pin DRIVER duty cycle<10% −0.8 +3 A
ISRSENSE current on pin SRSENSE −3- mA
General
Ptot total power dissipation Tamb <80°C - 0.45 W
Tstg storage temperature −55 +150 °C junction temperature −40 +150 °C
VESD electrostatic discharge
voltage
class 2
human body
model
[1] - 2000 V
machine model [2] -200 V
charged device
model
-500 V
Table 4. Thermal characteristics
Rth(j-a) thermal resistance from junction
to ambient
in free air 150 K/W
Rth(j-c) thermal resistance from junction
to case K/W
NXP Semiconductors TEA1791T
GreenChip synchronous rectifier controller
10. Characteristics
[1] The VCC stop voltage is Vstartup− Vhys.
Table 5. Characteristics
Tamb =25 °C; VCC=20 V; all voltages are measured with respect to ground (pin 2); currents are positive when flowing into
the IC; unless otherwise specified.
Supply voltage management (pin VCC)
Vstartup start-up voltage 8.2 8.5 8.8 V
Vhys hysteresis voltage [1] -0.5 - V
ICC(oper) operating supply current VCC =8V (VCC under normal operation; load on pin DRIVER
-0.95 - mA
Synchronous rectification sense input (pin SRSENSE)
Vact(drv) driver activation voltage −340 −310 −280 mV
Vreg(drv) driver regulation voltage −65 −55 −45 mV
Vdeact(drv) driver deactivation
voltage −12 - mV
td(act)(drv) driver activation delay
time
-125 - ns
tact(sr)(min) minimum synchronous
rectification
Short time 1.5 2.0 2.5 μs
Long time 1.7 2.2 2.7 μs
Driver (pin DRIVER)
Isource source current VCC =15V;
voltageon pin DRIVER = 2V −0.3 −0.25 −0.2 A
Isink sink current VCC =15V
voltage on pin DRIVER = 2V 1 1.4 - A
voltage on pin
DRIVER= 9.5V
2.2 2.7 - A
Vo(max) maximum output voltage VCC =15V - 10 12 V

Partno	Mfg	Dc	Qty	Available	Descript
TEA1791T	NXP	N/a	6600	avai	Synchronous rectification controller suitable for both high-side and low-side control