tea1752t NXP Semiconductors, tea1752t Datasheet - Page 19

• Manufacturer Part Number: tea1752t
• Description: Greenchip Iii Smps Control Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1752T_LT
Product data sheet
7.3.7 Maximum on-time
7.3.8 Overvoltage protection (FBAUX pin)
An internal current source charges the capacitor to V = I
of approximately 0.63 V.
The start level and the time constant of the increasing primary current level can be
externally adjusted by changing the values of R
The soft start current I
voltage on pin FBSENSE has reached 0.63 V the flyback converter starts switching.
The charging current I
0.63 V. If the voltage on pin FBSENSE exceeds 0.63 V, the soft start current source limits
the current. Once the flyback converter has started, the soft start current source is
switched off.
The flyback controller limits the ‘on-time’ of the external MOSFET to 40 μs (typical). When
the ‘on-time’ is longer than 40 μs, the IC stops switching and enters the safe restart mode.
An output overvoltage protection is implemented in the GreenChip III series. This
operates for the TEA1752(L)T by sensing the auxiliary voltage via the current flowing into
pin FBAUX during the secondary stroke. The auxiliary winding voltage is a well defined
replica of the output voltage. Voltage spikes are averaged by an internal filter.
If the output voltage exceeds the OVP trip level, an internal counter starts counting
subsequent OVP events. The counter has been added to prevent incorrect OVP detection
which might occur during ESD or lightning events. If the output voltage exceeds the OVP
trip level a few times and then not again in a subsequent cycle, the internal counter counts
down at twice the speed it uses when counting up. However, when typically eight cycles of
subsequent OVP events are detected, the IC assumes a true OVP and the OVP circuit
switches the power MOSFET off. As the protection is latched, the converter only restarts
after the internal latch is reset. In a typical application the mains should be interrupted to
reset the internal latch.
τsoftstart
Fig 15. Soft start-up of flyback
=
3
×
All information provided in this document is subject to legal disclaimers.
R
SS2
R SENSE2
×
start(soft)PFC
start(soft)fb
S2
Rev. 02 — 24 June 2010
C
R SS2
C SS2
SS2
is switched on when V
10
FBSENSE
flows if voltage on pin FBSENSE is below approximately
3 μA
I
start(soft)fb
TEA1752T; TEA1752LT
ocp level
≤ 60 μA
SS2
and C
SOFT START
CONTROL
CC
OCP
start(soft)fb
reaches V
GreenChip III SMPS control IC
SS2
.
014aaa748
× R
startup
SS2
© NXP B.V. 2010. All rights reserved.
, with a maximum
. When the
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