AN10907
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© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
42 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
The slow (dis)charge speed is used for the lower frequency range where V
SSHBC/EN
is
above 5.6 V. In the lower frequency range the current in the converter reacts strongly to
frequency variations.
Burst mode
The soft-start capacitor is neither charged nor discharged during the no-operation time in
burst mode operation. The soft-start voltage does not change during this time.
8.6.2.3
SNSFB, SSHBC/EN and soft-start reset - operating frequency control
The operating frequency can be controlled by the SNSFB and SSHBC/EN simultaneously.
SSHBC/EN is dominant to provide protection and soft-start capability. In addition, there is
an internal soft-start reset mechanism that overrules both SNSFB and SSHBC/EN control
inputs and immediately sets the frequency to maximum.
8.6.2.4
Soft-start reset
Some protection functions require a fast correction of the operating frequency to the
maximum value, but it is not needed to stop switching. The overcurrent protection is an
example (see
When this protection is activated, the control input of the oscillator is disconnected
internally from the soft-start capacitor at pin SSHBC/EN and the switching frequency is
immediately set to maximum. In most cases, the change to the maximum switching
Fig 28. OverCurrent Regulation (OCR) during start-up
500 mV
typ
−
500 mV
typ
V
SNSCURHBC
160
μ
A
typ
40
μ
A
typ
−
40
μ
A
typ
−
160
μ
A
typ
I
SSHBC/EN
V
SSHBC/EN
8 V
typ
5.6 V
typ
3.2 V
typ
V
O
V
regulate
0
0
t
t
t
t
Fast soft-start sweep (charge and discharge)
Slow soft-start sweep (charge and discharge)
001aal452
