AN10907
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© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
38 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
8.5.1 HBC Open Loop Protection (OLP)
The resonant controller of the TEA1613T contains an Open-Loop Protection (OLP). This
protection monitors the voltage on SNSFB. When it exceeds 7.7 V, the protection timer is
started.
In normal operating conditions, the optocoupler current is between 0.66 mA and 2.2 mA
which pulls down the voltage at pin SNSFB. If an error occurs in the feedback loop, the
current can become less than 260
A which leads to an open loop protection.
Burst mode and open loop protection
To implement a burst mode, a resistor divider is connected between SNSFB and ground.
The impedance of this resistor divider should be significantly higher than 30 k
to keep
the Open Loop Protection function. If the lower resistance value is lower, the voltage is
lower than the threshold voltage of 7.7 V. This disables open loop error detection.
Fig 24. SNSFB V-I characteristics
(1) V
BOOST
= 310 V DC
(2) V
BOOST
= 350 V DC
(3) V
BOOST
= 390 V DC
Fig 25. SNSFB voltage to output power characteristics examples
0
I
SNSFB
V
open
= 8.4 V
0.66 mA
= I
fmin
V
RFMAX
2.2 mA
= I
fmax
0
0
V
SSHBC
= 8 V
260
μ
A
= I
OLP
V
OLP
= 7.7 V
V
fmin
= 6.4 V
V
fmax
= 4.1 V
V
clamp,fmax
= 3.2 V
V
SNSFB
8 mA
= I
clamp,max
001aal448
2.5 V = V
fmax
1.5 V = 0.6
×
V
fmax
P
o
(W)
0
250
200
100
150
50
001aal449
5.4
5.6
5.2
5.8
6.0
SNSFB
(V)
5.0
(1)
(2)
(3)
