AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
52 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
When the operating frequency remains at, or close to, maximum frequency for a longer
period, a fault condition is assumed and a protection activated.
The HFP senses the voltage at pin RFMAX. This voltage indicates the actual operating
frequency. When the frequency is higher than approximately 75 % of the frequency range
(RFMAX = 1.83 V), the protection timer is started.
Remark:
During normal regulation, the maximum frequency leads to only 60
of the
present range and the voltage at pin RFMAX is 1.5 V maximum.
8.5 HBC feedback (SNSFB)
A typical power supply application contains mains insulation in the HBC. On the
secondary (mains insulated) side, the output voltage is compared to a reference and
amplified. The TEA1713 is normally placed on the primary side. The output of the error
amplifier is transferred to the primary side via an OPTO coupler. The output of the OPTO
coupler on the primary side can be connected directly to SNSFB.
The SNSFB pin supplies the OPTO coupler from an internal voltage source of 8.4 V via an
internal series resistor of 1.5 k
. This internal series resistance allows spike filtering by an
external capacitor at the pin if needed.
The feedback input has a threshold current of 0.66 mA at which the frequency is minimum
to ensure sufficient bias current for proper working of the opto coupler. The maximum
frequency controlled by SNSFB is reached at 2.2 mA. This is approximately 60 % of the
total preset frequency range. The remaining upper part of the frequency range can only be
reached by control of SSHBC/EN for soft-start or protection.
Fig 29. Typical basic SNSFB application
001aal039
V+
8.4 V
3.2 V
21 SNSFB
CONTROL
TEA1713
1.5 k
Ω
