AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
10 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
17
SNSCURHBC
Sense input for the momentary current of the HBC. If the voltage level (that represents the
primary current) becomes too high, internal comparators determine the regulation to a higher
frequency (SNSCURHBC =
0.5 V) or protect (SNSCURHBC =
1 V) by switching immediately
to maximum frequency.
The provided additional current from SNSCURHBC can compensate variations at protection
level, caused by HBC input voltage variations. This current leads to a voltage offset across the
external series resistance value. The current measurement resistor and an extra series
resistance, which has a typical value of 1 k
, normally provide this series resistance .
18
SGND
Signal ground, reference for IC.
19
CFMIN
Oscillator pin.
The value of the external capacitor determines the minimum switching frequency of the HBC. In
combination with the resistor value on RFMAX, it sets the operating frequency range.
A triangular waveform is generated on the CFMIN capacitor (V
low(CFMIN)
= 1 V and
V
high(CFMIN)
= 3 V)) to facilitate switching timing. A fixed minimum (dis)charging current of
150
A determines the minimum frequency. During special conditions, the (dis)charging current
is reduced to 30
A to slow down the charging temporarily.
An internal function limits the operating frequency to 670 kHz.
20
RFMAX
Oscillator frequency pin.
The value of the resistor connected between this pin and ground, determines the frequency
range. Both the minimum and maximum frequencies of the HBC are preset. CFMIN sets the
minimum frequency. The absolute maximum frequency is internally limited to 670 kHz.
The voltage on RFMAX and the value of the resistor connected to it, determine the variable part
(in addition to the fixed 150
A) of the (dis)charging current of the CFMIN capacitor. The voltage
on RFMAX can vary between 0 V (minimum frequency) and 2.5 V (maximum frequency).
SNSFB and the SSHBC/EN function drive the RFMAX voltage (running frequency).
The protection timer is started when the voltage level is above 1.88 V. An error is assumed
when the HBC is operating at high frequency for a longer time.
21
SNSFB
Sense input for HBC output regulation feedback by voltage.
Sinking a current from SNSFB creates the feedback voltage on SNSFB. The regulation voltage
is produced by feeding this current through a 1.5 k
internal resistor which is internally
connected to 8.4 V.
The regulation voltage range is from 4.1 V to 6.4 V. It corresponds with the maximum and
minimum frequencies that are controlled by SNSFB. The SNSFB range is limited to 65 % of the
maximum frequency preset by RFMAX.
The provision of open-loop detection activates the protection timer when SNSFB exceeds 7.7 V.
Table 2.
Pinning overview
…continued
Pin
Name
Functional description