TEA1541P PHILIPS [NXP Semiconductors], TEA1541P Datasheet - Page 8

• Manufacturer Part Number: TEA1541P
• Description: SMPS control IC with synchronization function
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
6.3
The IC uses current mode control for its good line
regulation behaviour. The primary current is sensed
indirectly via the voltage at pin DEM.
The ‘on-time’ of the external MOSFET is controlled by the
voltage on pin CTRL which is compared with the internal
simulated primary current information. For pin CTRL
voltages (V
calculated by the equation:
where:
6.4
In synchronized mode, the switching frequency of the
SMPS f
at pin CTRL. Synchronized mode prevents noise
disturbance on the CRT monitor screen. Synchronizing
pulses whose frequency is outside of the f
window of 26 to 54 kHz are divided by an internal
frequency divider. A small frequency hysteresis exists to
ensure a stable frequency switch-over. In unsynchronized
mode, the system runs at f
mode, at very low power (standby) levels, the frequency of
the VCO and consequently the SMPS switching frequency
is reduced linearly to its low value of approximately 6 kHz
(see Figs 4 and 6).
2003 Aug 11
t
on
t
V
I
cycle.
SMPS control IC with
synchronization function
on
DEM
PCS
CTRL
=
: the on-time
: the current drawn from pin DEM during the primary
Primary current regulation
Oscillator
: an internal constant which is approximately 0.9.
smps
PCS
: the voltage on pin CTRL
CTRL
is controlled by the synchronizing pulses f
1.6 V
------------------------------ - ns
) between 1 and 1.6 V, the on-time is
I
–
DEM
CTRL
osc
(26 kHz). In unsynchronized
osc
and f
smps(max)
sync
8
6.5
The system always operates in discontinuous conduction
mode to ensure demagnetization of the output transformer
core. A primary cycle only starts when the secondary cycle
has ended.
Pin DEM protects against an output short-circuit on a
cycle-by-cycle basis, by immediately lowering the
switching frequency to give a longer off-time and a lower
operating power.
Demagnetization detection is suppressed automatically at
the start of each secondary cycle for a period t
Suppression of demagnetization detection is necessary for
applications where the transformer has a large leakage
inductance, at low output voltages and at start-up.
If, due to a fault condition, pin DEM is left open circuit,
operation of the flyback converter supply immediately
stops, and restarts when the fault situation is removed and
pin DEM is reconnected.
If, during start-up, a fault condition causes pin DEM to be
shorted to ground, operation of the flyback converter
supply stops after the first cycle, and the IC then begins a
restart cycle. This situation continues until the short-circuit
is removed. Short-circuit protection is also active at full
power to ensure limitation of peak current.
handbook, halfpage
Fig.6
f smps(max)
Demagnetization
(kHz)
f osc
f
Switching frequency as a function of the
synchronizing frequency.
f sync
(min)
(max)
f sync
Product specification
2
(max)
f sync
TEA1541
suppr
MDB086
(kHz)
.
f