TEA1713T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 2 — 9 February 2011 24 of 47
NXP Semiconductors
TEA1713T
Resonant power supply control IC with PFC
The oscillator is controlled by the slope of the half-bridge. The oscillator charge current is
initially set to a low value I
osc(red)
(typ. 30 μA). When the start of the half-bridge slope is
detected, the charge current is increased to its normal value. This feature is used in
combination with the adaptive non-overlap time function as described in Section 7.8.4.2
and Figure 11
. Since the half-bridge slope normally starts directly after the MOSFET is
switched off, the length of time the oscillator current is low will be negligible under normal
operating conditions.
7.8.6 HBC feedback input (pin SNSFB)
In a typical power supply application, the output voltage is compared and amplified on the
secondary side. The output of the error amplifier is transferred to the primary side via an
opto-coupler. This opto-coupler can be connected directly to the SNSFB pin.
The SNSFB pin supplies the opto-coupler from an internal voltage source V
pu(SNSFB)
(typ. 8.4 V) with a series resistance R
O(SNSFB)
. The series resistance allows spike filtering
via an external capacitor. To ensure sufficient bias current for the opto-coupler, the
feedback input has a threshold current I
fmin(SNSFB)
(typ. 0.66 mA) at which the frequency is
at a minimum. The maximum frequency is reached at I
fmax(SNSFB)
(typ 2.2 mA). The
maximum frequency that can be reached via the SNSFB pin is lower (typ. 60 %) than the
maximum frequency that can be reached via the SSHBC/EN pin. Figure 14
shows the
relationship between I
SNSFB
, V
SNSFB
and V
RFMAX
.
A: C
fmin
=high, R
fmax
=high
B: C
fmin
=low, R
fmax
=low
C: C
fmin
= low, R
fmax
= too low
Fig 13. Function of R
fmax
and C
fmin
f
limit(HB)
f
max(B)
V
fmax(fb)(RFMAX)
V
fmax(ss)(RFMAX)
V
RFMAX
A
B
C
f
max(A)
f
min(B and C)
f
min(A)
0
f
HB
014aaa86
