tea1751lt NXP Semiconductors, tea1751lt Datasheet - Page 15

• Manufacturer Part Number: tea1751lt
• Description: Greenchip Iii Smps Control Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1751T_LT_1
Product data sheet
7.3.4 Demagnetization (FBAUX pin)
7.3.5 Flyback control / time-out (FBCTRL pin)
The driver output is latched in the logic, preventing multiple switch-on.
The system is always in quasi-resonant or discontinuous conduction mode. 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), thereby reducing the power level.
Demagnetization recognition is suppressed during the first t
This suppression may be necessary at low output voltages and at start-up and in
applications where the transformer has a large leakage inductance.
If pin FBAUX is open circuit or not connected, a fault condition is assumed and the
converter stops operating immediately. Operation restarts as soon as the fault condition is
removed.
The pin FBCTRL is connected to an internal voltage source of 3.5 V via an internal
resistor (typical resistance is 3 k ). As soon as the voltage on this pin is above 2.5 V (typ),
this connection is disabled. Above 2.5 V the pin is biased with a small current. When the
voltage on this pin rises above 4.5 V (typ), a fault is assumed and switching is inhibited. In
the TEA1751 a restart will then be made, while in the TEA1751L the protection will be
latched.
When a small capacitor is connected to this pin, a time-out function can be created to
protect against an open control loop situation. (see
function can be disabled by connecting a resistor (100 k ) to ground on the FBCTRL pin.
If the pin is shorted to ground, switching of the flyback controller is inhibited.
Fig 10. Peak current control of flyback part
FBSENSE peak voltage
Rev. 01 — 10 July 2008
V
sense
max
0.52 V
0.13 V
(fb)
cycle skip
flyback
mode
PFC off
TEA1751T; TEA1751LT
frequency
reduction
flyback
1.4 V
1.5 V
Figure 11
PFC on
2.0 V
discontinuous
GreenChip III SMPS control IC
flyback
sup(xfmr_ring)
or QR
and
V
FBCTRL
Figure
014aaa160
© NXP B.V. 2008. All rights reserved.
time (2 s typ).
12) The time-out
15 of 29