Datasheet
TEA1832LTS All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 1 — 15 December 2014 10 of 23
NXP Semiconductors
TEA1832LTS
GreenChip SMPS control IC
7.11 Output Short Circuit Protection (OSCP)
A flyback controller operating in CCM at a fixed frequency turns on the primary MOSFET
after a predefined period (see Figure 10
). The minimum on-time equals the blanking time.
If after the blanking time the measured peak current (V
ISENSE
) is higher than the I
peak
regulation level, the driver is switched off.
The output voltage can drop, for instance, because a load is too high or a short circuit
event occurs. If the output voltage drops, the decrease of the transformer current during
the secondary stroke time (t
sec
) becomes less. As a result, the next cycle starts at a higher
peak current.
Also, at the next cycle, the minimum on-time equals the blanking time. During this
blanking time, the peak current can increase to above the targeted regulation level. If the
transformer current does not decrease sufficiently during the secondary stroke, the peak
current can continuously increase to such a level that the transformer saturates
(see Figure 10
).
To avoid this continuous peak current increase, also called runaway, the IC features a
special protection (see Figure 11
).
Fig 10. Peak current runaway
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