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TEA1762T/N2/DG,118

P1-P3P4-P6P7-P9P10-P12P13-P15
TEA1762T_2 © NXP B.V. 2007. All rights reserved.
Product data sheet Rev. 02 — 25 April 2007 4 of 15
NXP Semiconductors
TEA1762T
GreenChip synchronous rectifier controller
7.1 Start-up and undervoltage lock-out
The IC leaves the under-voltage lock-out state and activates the synchronous rectifier
circuitry and also the voltage/current sense circuitry as soon as the voltage on the V
CC
pin
is above 8.6 V (typical). As soon as the voltage drops below 8.1 V (typical), the
under-voltage lock-out state is re-entered and the SR driver output is actively kept low and
also the opto driver outputs are disabled.
7.2 Synchronous rectification
After a negative voltage (−310 mV typical) is sensed on the SRSENSE pin, the driver
output voltage is made 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. As soon as 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 2 µs (typical). This will eliminate 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 fast 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 no-load operation. The zero current is detected
by sensing a −12 mV level on the SRSENSE pin. See Figure 3.
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.
Fig 3. Synchronous rectification
014aaa057
0 V
−12 mV
−55 mV
−310 mV
0 A
0 A
0 V
V
SRSENSE
V
DRIVER
Primary
current
Secondary
current
TEA1762T_2 © NXP B.V. 2007. All rights reserved.
Product data sheet Rev. 02 — 25 April 2007 5 of 15
NXP Semiconductors
TEA1762T
GreenChip synchronous rectifier controller
7.3 SMPS output voltage and current regulation
The output voltage of the flyback Switched Mode Power Supply (SMPS) can be controlled
by sensing the output voltage via the VSENSE pin. The feedback loop via the primary
controller can regulate the output voltage of the switched mode power supply by
regulating the voltage on the VSENSE pin to 2.5 V above the voltage on pin SENSEGND.
Also the output current of the flyback SMPS can be controlled or limited. The voltage on
the ISENSE pin is regulated or limited to 50 mV above the voltage on pin POWERGND.
7.4 Opto outputs
The opto output is intended to drive an opto coupler (see Figure 5). The opto outputs have
an open drain output configuration. The maximum sink current is internally limited to 5 mA
(typical). The outputs are linearly controlled via the VSENSE and ISENSE input pins. An
over-temperature situation will switch the protection opto output (OPTOPROT) to its
maximum sink current.
During start-up (V
CC
<V
startup
) and undervoltage lock-out the outputs are disabled.
7.5 Protection input
The PROTECT pin is a general purpose input pin which can be used for additional
protection of the switched mode power supply. With a Negative Temperature Coefficient
(NTC) thermistor external temperature protection can be provided, e.g. the external power
switches and transformer can be protected against high temperatures. With a Zener diode
a secondary overvoltage protection can be made.
7.6 Reference voltage output
The reference voltage output pin can be used for supplying external circuitry. The
maximum output current must be limited to 1 mA.
The reference voltage is activated as soon as the start-up voltage is reached on the V
CC
pin and switched off again after the V
CC
pin voltage drops below the V
CC
stop level.
7.7 Supply management
All (internal) reference voltages are derived from a temperature compensated, on-chip
band gap circuit. The reference voltage is trimmed to an accuracy within 1 %.
7.8 OverTemperature Protection (OTP)
The IC provides an accurate internal overtemperature protection of 150 °C (typical). The
IC will maximize the current of pin OPTOPROT as soon as the internal temperature limit is
reached. The opto signal can be used on the primary side of the flyback controller to
activate the SMPS protection or limit the output power. As soon as the overtemperature
condition is solved, normal operation will resume.
TEA1762T_2 © NXP B.V. 2007. All rights reserved.
Product data sheet Rev. 02 — 25 April 2007 6 of 15
NXP Semiconductors
TEA1762T
GreenChip synchronous rectifier controller
7.9 Driver
The driver circuit to the gate of the external power MOSFET has a source capability of
typically 250 mA and a sink capability of typically 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 (V
CC
<V
startup
) and undervoltage lock-out the driver output
voltage is actively pulled low.
7.10 Power ground and sense ground
The TEA1762T has two ground connections. The sense ground ensures an increased
accuracy of the output voltage of the switched mode power supply and can also be used
to compensate for cable losses on the output of the converter. The grounds are internally
connected via two anti-parallel diodes.
8. Limiting values
Table 3. Limiting values
In accordance with the Absolute Maximum Rating System (IEC 60134). All voltages are measured with respect to power
ground (pin 2); positive currents flow into the chip. The voltage ratings are valid provided other ratings are not violated; current
ratings are valid provided the maximum power rating is not violated.
Symbol Parameter Conditions Min Max Unit
Voltages
V
CC
supply voltage continuous −0.4 +38 V
V
OPTOREG
voltage on pin OPTOREG continuous −0.4 +38 V
V
OPTOPROT
voltage on pin OPTOPROT continuous −0.4 +38 V
V
SRSENSE
voltage on pin SRSENSE continuous - +120 V
V
VSENSE
voltage on pin VSENSE continuous −0.4 +5 V
V
ISENSE
voltage on pin ISENSE −0.4 +5 V
V
PROTECT
voltage on pin PROTECT −0.4 +5 V
V
SENSEGND
voltage on pin SENSEGND
[1]
−0.4 +0.4 V
Currents
I
OPTOREG
current on pin OPTOREG - +6 mA
I
OPTOPROT
current on pin OPTOPROT - +6 mA
I
DRIVER
current on pin DRIVER duty cycle < 10 % −0.8 +3 A
I
VREF
current on pin VREF −2- mA
I
SRSENSE
current on pin SRSENSE −3- mA
General
P
tot
total power dissipation T
amb
<80°C - 0.65 W
T
stg
storage temperature −55 +150 °C
T
j
junction temperature −20 +150 °C
P1-P3P4-P6P7-P9P10-P12P13-P15

TEA1762T/N2/DG,118

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NXP Semiconductors
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Power Factor Correction - PFC 3.5V 5mA 10%
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