NXP Semiconductors AN10907, Примечание к применению

Страница: 61 / 82

AN10907 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
Application note Rev. 1 — 28 December 2010 61 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
10.3.2 UnderVoltage Protection (UVP) output
The TEA1613T has undervoltage protection intended for monitoring the HBC output
voltage. It is one of the functions that is combined on the SNSOUT/PFCON pin.
10.3.2.1 Auxiliary winding
When dealing with a mains insulated converter, the HBC output voltage can be measured
via the auxiliary winding of the resonant transformer. To accurately measure the
secondary voltage of the primary circuit auxiliary winding, a special transformer
construction is needed.
To facilitate correct working, it is important that this winding has a good coupling with the
secondary winding(s) and a minimum coupling with the primary winding. This is to obtain
a good representation of the output voltage situation. For more details refer to
Section 6.3.3.1 and Figure 6 .
To meet the mains insulation requirements, triple insulated wire can be used.
10.3.2.2 Principle of operation
The voltage is sensed at the SNSOUT/PFCON pin via an external rectifier and resistor
divider. Undervoltage is detected when the SNSOUT/PFCON voltage drops below 2.35 V.
When detecting UVP the TEA1613T starts the protection timer by charging it with 100

A.
When the undervoltage state remains until the timer reaches the protection level, the
controller stops and is then re-started by the restart timer.
At start-up, the SNSOUT/PFCON voltage normally starts at a level lower than 2.35 V. To
prevent undesired protection during start-up, the timer setting must allow sufficient time
for start-up to charge the SNSOUT/PFCON voltage to a value above 2.35 V.
In applications where the TEA1613T is supplied from an auxiliary winding (to SUPIC), the
SUPIC monitoring can also activate a protection when an error condition results in a drop
of the output voltage (see
Section 6.2.2 ).
10.3.2.3 Connecting external measurement circuits
When re-start protection is required for another detection circuit, it can be added to
SNSOUT/PFCON by means of a series diode. An example of external temperature
protection is given in
Figure 45 .
10.3.3 OVP and UVP combinations
10.3.3.1 Circuit configurations
The following list contains examples of configurations for which certain functionality on the
SNSOUT/PFCON pin is disabled.
•
OVP functional and UVP disabled (refer to Section 10.3.3.2 )
•
UVP functional and OVP disabled (refer to Section 10.3.3.3 )
•
Both OVP and UVP disabled (refer to Section 10.3.3.4 )
Note that in the examples given in the referenced sections, the PFCON signal can still be
generated for burst mode operation.