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TEA1755LT/1Y

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P35
TEA1755LT All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 1.1 — 13 March 2015 16 of 35
NXP Semiconductors
TEA1755LT
HV start-up DCM/QR flyback controller with integrated DCM/QR PFC
controller
7.3.4 Demagnetization (FBAUX pin)
The system is always in QR or DCM. The internal oscillator does not start a new primary
stroke until the previous secondary stroke has ended.
Demagnetization features a cycle-by-cycle output short-circuit protection by immediately
lowering the frequency (longer off-time) and reducing the power level.
Demagnetization recognition is suppressed during the first t
sup(xfmr_ring)
time of 2.2 s.
This suppression can be necessary at low output voltages, during start-up and in
applications where the transformer has a large leakage inductance.
If the FBAUX pin is open-circuit or not connected, a fault condition is assumed and the
converter immediately stops. Operation restarts when the fault condition is removed.
7.3.5 Flyback control/time-out (FBCTRL pin)
The FBCTRL pin is connected to an internal voltage source of 7 V using an internal
13.2 k resistor. When V
FBCTRL
> 5.5 V, the resistor is disconnected. The pin is biased
with a 29 A current. When V
FBCTRL
> 7.75 V, a fault is assumed, switching is stopped and
a latched protection is activated.
If a capacitor and resistor are connected in series to the pin, a time-out function is created
which protects against open control loop situations. See Figure 12
and Figure 13. The
time-out function is disabled by connecting a resistor (200 k) to ground on the FBCTRL
pin.
If the pin is short-circuited to ground, switching of the flyback controller is stopped.
Under normal operating conditions, the converter regulates the output voltage. V
FBCTRL
varies between 0.77 V at minimum output power and 4.9 V at maximum output power.
Fig 11. Flyback part peak current control
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TEA1755LT All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 1.1 — 13 March 2015 17 of 35
NXP Semiconductors
TEA1755LT
HV start-up DCM/QR flyback controller with integrated DCM/QR PFC
controller
7.3.6 Burst mode operation (FBCTRL pin)
The flyback controller enters the burst mode when the output power is very low and the
switching frequency is < 25 kHz. In burst mode, the flyback converter switching frequency
is 36.5 kHz. The minimum flyback sense voltage of 232 mV, in combination with an offset
voltage (see Section 7.3.3
), determines the peak current.
A burst cycle starts when one of the following is made:
• V
FBCTRL
> 2.4 V
• V
CC
<V
prot(UVLO)
. This voltage level is typically 0.8 V > V
th(UVLO)
The burst cycle is stopped when V
FBCTRL
<0.77V.
In burst mode, the internal IC supply current is reduced to improve the no-load and
low-load input power.
The burst mode is exited and normal operation resumes when the V
FBCTRL
> 2.8 V (see
Figure 14
).
Fig 12. Time-out protection circuit
Fig 13. TEA1755LT latched time-out protection (signals)
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TEA1755LT All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 1.1 — 13 March 2015 18 of 35
NXP Semiconductors
TEA1755LT
HV start-up DCM/QR flyback controller with integrated DCM/QR PFC
controller
7.3.7 Soft-start (FBSENSE pin)
To prevent audible transformer noise during start-up, the soft-start function slowly
increases the transformer peak current. Place a capacitor C
SS2
in parallel with resistor
R
SS2
(see Figure 15) to implement the soft-start function.
An internal current source charges the capacitor to:
(5)
with a maximum of 0.55 V.
The start level and the time constant of the increasing primary current level can be
adjusted externally by changing the values of R
SS2
and C
SS2
.
(6)
The soft-start current I
start(soft)fb
switches on when V
CC
reaches V
startup
. When the
V
FBSENSE
reaches 0.55 V, the flyback converter starts switching.
The charging current I
start(soft)fb
flows when the V
FBSENSE
is < 0.55 V. If V
FBSENSE
exceeds
0.55 V, the soft-start current source starts limiting the current. After the flyback converter
has started, the soft-start current source is switched off.
When the IC is operating in the burst mode, the soft-start function is switched off.
Fig 14. Burst mode operation
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R
SS2
=
soft s– tart 3 R
SS2
C
SS2
=
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P35

TEA1755LT/1Y

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NXP Semiconductors
Description:
AC/DC Converters TEA1755LT/SO16//1/REEL 13 Q1 DP
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