NXP Semiconductors AN10907, Примечание к применению

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Application note Rev. 1 — 28 December 2010 40 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
8.6.1.1 Switching on and off using SSHBC/EN
When a voltage is present at pin SUPHV or at pin SUPIC, a current of 42

A from the
SSHBC/EN pin charges the external capacitor. If the pin is not pulled-down, this current
initially lifts the voltage to 3.0 V. Since this is above the enable level (2.2 V), the IC is
enabled.
The IC can be disabled by pulling down the SSHBC/EN pin below 2.2 V. The HBC
continues until the low-side stroke is active. The pull-down current must be larger than the
current capability from the internal soft-start clamp: i.e. 42

A.
8.6.1.2 Hold and continue
The SNSBURST function can be used to start and stop the HBC. This method is intended
for burst-mode operation to switch off the converters for only a short time. It is possible to
either operate only the HBC in burst-mode or both HBC + PFC simultaneously (by use of
the SNSOUT/PFCON signal). The possibilities are similar to SSHBC/EN with the main
difference being that HBC continues without soft-start. For more details on burst mode
operation, see
Section 9.1 .
8.6.2 Soft-start HBC
The soft-start function for the resonant converter is provided by SSHBC/EN.
The relationship between switching frequency and output current/power is not constant. It
depends strongly on output voltage and boost voltage and the relationship can be
complex. To ensure that the resonant converter starts or re-starts with safe currents, the
TEA1613T has a soft-start function.
The soft-start function forces a start at high frequency so that currents are acceptable in
all conditions. It slowly decreases the frequency until the output voltage regulation has
taken over the frequency control. The limitation of the output current during start-up also
limits the output voltage rise and prevents an overshoot.
During soft-start, and in parallel with the soft-start frequency sweep, the SNSCURHBC
function monitors the primary current and can activate regulation in case of a (temporary)
overpower situation.
The soft-start uses the voltage at pin SSHBC/EN. The timing (duration) of the soft-start
event is set by an external capacitor on SSHBC/EN.
As the SSHBC/EN is also used as an input enable, the soft-start functionality is above the
enable related voltage levels (see
Figure 27 ).