TEA1751LT/N1 NXP Semiconductors, TEA1751LT/N1 Datasheet - Page 17

• Manufacturer Part Number: TEA1751LT/N1
• Description: AC-DC, PFC, FLYBACK, CNTRL, 16SOIC
• Manufacturer: NXP Semiconductors

Specifications of TEA1751LT/N1

• Input Voltage: 276V
• Output Current: 1.2A
• Output Voltage: 11V
• No. Of Outputs: 2
• Power Dissipation Pd: 600mW
• Voltage Regulator Case Style: SOIC
• No. Of Pins: 16
• Operating Temperature Range: -40°C To
• Supply Voltage Range: 21V To 23V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

NXP Semiconductors
TEA1751T_LT_2
Product data sheet
7.3.6 Soft start-up (pin FBSENSE)
7.3.7 Maximum on-time
7.3.8 Overvoltage protection (FBAUX pin)
To prevent audible transformer noise during start-up, the transformer peak current, I
slowly increased by the soft start function. This can be achieved by inserting a resistor and
a capacitor between pin 10, FBSENSE, and the current sense resistor.
An internal current source charges the capacitor to V = I
of approximately 0.5 V.
The start level and the time constant of the increasing primary current level can be
adjusted externally by changing the values of R
The soft start current I
voltage on pin FBSENSE has reached 0.5 V, the flyback converter starts switching.
The charging current I
approximately 0.5 V. If the voltage on pin FBSENSE exceeds 0.5 V, the soft start current
source starts limiting the current. After 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 works
for the TEA1751(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 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
τsoftstart
Fig 14. Soft start-up of flyback.
=
3
×
R
SS2
Rev. 02 — 23 December 2009
×
start(soft)fb
start(soft)(PFC)
C
R SENSE2
S2
SS2
R SS2
C SS2
is switched on as soon as V
flows as long as the voltage on pin FBSENSE is below
10
FBSENSE
I start(soft)fb ≤ 60 μA
TEA1751T; TEA1751LT
SS2
+
0.5 V
SOFT START
CONTROL
and C
OCP
start(soft)fb
GreenChip III SMPS control IC
SS2
CC
014aaa020
.
reaches V
× R
SS2
© NXP B.V. 2009. All rights reserved.
, with a maximum
startup
. When the
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DM
is