TEA1750 NXP Semiconductors, TEA1750 Datasheet - Page 15

• Manufacturer Part Number: TEA1750
• Description: GreenChip III SMPS control IC
• Manufacturer: NXP Semiconductors

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NXP Semiconductors
TEA1750_2
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.
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.
In normal operating conditions, when the converter is regulating the output voltage, the
voltage on the FBCTRL pin is between 1.4 V and 2.0 V (typical values) from minimum to
maximum output power.
Fig 10. Frequency control of flyback part
FBSENSE peak voltage
V
sense(fb)max
Rev. 02 — 15 December 2008
0.52 V
0.13 V
PFC burst mode
cycle skip
flyback
mode
flyback
frequency
reduction
1.4 V
1.5 V
PFC on
Figure 11
2.0 V
discontinuous
flyback
or QR
GreenChip III SMPS control IC
V
FBCTRL
sup(xfmr_ring)
and
014aaa028
Figure
TEA1750
© NXP B.V. 2008. All rights reserved.
time (2 s typ).
12). The time-out
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