TEA1520T NXP [NXP Semiconductors], TEA1520T Datasheet - Page 7

• Manufacturer Part Number: TEA1520T
• Description: SMPS ICs for low-power systems
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
TEA152X_3
Product data sheet
8.5 Demagnetization
8.6 Minimum and maximum duty factor
8.7 OverCurrent Protection (OCP)
8.8 Short-circuit winding protection
Figure 5
the output voltage V
the factor N (determined by the turns ratio of the transformer).
system switches exactly at minimum drain voltage for ringing frequencies of 480 kHz, thus
reducing the switch-on losses to a minimum. At 200 kHz, the next primary stroke is
started at 33 before the valley. The switch-on losses are still reduced significantly.
The system operates in discontinuous conduction mode all the time. As long as the
secondary stroke has not ended, the oscillator will not start a new primary stroke. During
the first t
be necessary in applications where the transformer has a large leakage inductance and at
low output voltages.
The minimum duty factor of the switched mode power supply is 0 %. The maximum duty
factor is set to 75 % (typical value at 100 kHz oscillation frequency).
The cycle-by-cycle peak drain current limit circuit uses the external source resistor R
measure the current. The circuit is activated after the leading edge blanking time t
protection circuit limits the source voltage to V
current.
The short-circuit winding protection circuit is also activated after the leading edge blanking
time. If the source voltage exceeds the short-circuit winding protection voltage V
stops switching. Only a power-on reset will restart normal operation. The short-circuit
winding protection also protects in case of a secondary diode short circuit.
Fig 5.
suppr
shows a typical curve for a reflected output voltage N
Typical phase of drain ringing at switch-on (at N
seconds, demagnetization recognition is suppressed. This suppression may
o
phase
(see
( )
Rev. 03 — 23 March 2009
40
20
20
40
0
0
Figure
6) transferred to the primary side of the transformer with
200
400
source(max)
600
SMPS ICs for low-power systems
, and thus limits the primary peak
f (kHz)
V
mgt424
o
= 80 V)
800
Figure 5
V
o
of 80 V. This voltage is
TEA152x
© NXP B.V. 2009. All rights reserved.
shows that the
swp
leb
, the IC
. The
7 of 17
I
to