NXP Semiconductors AN10881, Примечание к применению

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AN10881 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Application note Rev. 2 — 26 September 2011 75 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
At start-up, the SNSOUT voltage normally starts at a level lower than 2.35 V. The timer
setting must allow sufficient time for start-up to charge the SNSOUT voltage to a value
above 2.35 V, preventinfg undesired protection during start-up.
In applications where the TEA1713 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 5.2.2 ).
10.3.2.3 Severe voltage drop
When the voltage on SNSOUT drops to a low voltage, the Hold HBC and Hold PFC
functions on this input pin stop the HBC and PFC.
10.3.2.4 Connecting external measurement circuits
When restart protection is needed for other detection circuits, it can be added on
SNSOUT with a series diode.
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 pin is disabled.
•
OVP functional and UVP disabled (see Section 10.3.3.2 )
•
UVP functional and OVP disabled (see Section 5.3.3.3 )
•
Both OVP and UVP disabled (see Section 10.3.3.4 )
Remark: In the examples given, Burst mode operation can still be implemented
independent of the UVP and/or OVP functionality.
10.3.3.2 OVP functional and UVP disabled
In some applications preventing the activation of the undervoltage protection on SNSOUT
by disabling UVP can be required. This can be realized by adding a circuit that prevents
the voltage on SNSOUT from dropping below 2.35 V.
As a practical example, the voltage on SNSOUT can be prevented from dropping below a
preset voltage by externally adding a low impedance resistive divider, with a fixed voltage
and connecting it to SNSOUT via a diode. This simple circuit is not accurate but it does
provide the basic capability to disable the UVP function of SNSOUT.
Remark: The diode is blocking for higher voltage values on SNSOUT so that the
overvoltage protection is still functional.