AN10881
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Application note
Rev. 2 — 26 September 2011
55 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
The TEA1713 also offers the possibility to switch on/off using the SNSOUT function. This
function is intended for Burst mode operation where the duration of the on-states and
off-states are short.
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 from the SSHBC/EN
pin charges the external capacitor. If the pin is not pulled-down, this current increases the
voltage to 8.4 V. Since this is above the level to enable the operation of PFC (1.2 V) and
PFC + HBC (2.2 V), the IC is completely enabled.
The IC can be completely disabled by pulling down the SSHBC/EN pin below 1.2 V. The
PFC controller stops switching immediately, but 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.
PFC only active
By pulling the SSHBC/EN voltage below the enable PFC + HBC operation level (2.2 V),
but keeping it above the enable PFC operating level (1.2 V), only the HBC is disabled.
This can be used when there is another power converter connected to the boost voltage
of the PFC. The low-side power switch of the HBC is on when the HBC is disabled via the
SSHBC/EN pin.
HBC only active
The TEA1713 is not designed to provide this operation mode but it can be realized by
forcing a voltage higher than 2.63 V (but below 5 V) on SNSBOOST. This way the output
overvoltage protection of the PFC is activated and the PFC operation stopped (put on
hold). The HBC operates because SNSBOOST exceeds its start level of 2.3 V
(boost UVP).
This mode of operation is not likely to be required by an application, but it can be useful for
starting up and debugging purposes during analyses or evaluation.
8.6.1.2
Hold and continue
The SNSOUT function can be used to start and stop the PFC and HBC. This method is
intended for Burst mode operation to switch off the converters for only a short time. It is
possible to operate only the HBC in Burst mode or both HBC + PFC simultaneously. The
possibilities are similar to SSHBC/EN with the main difference being that HBC continues
without soft-start (see
8.6.2 Soft-start HBC
SSHBC/EN provides the soft-start function for the resonant converter.
The relation between switching frequency and output current/power is not constant. It is
highly dependent on output and boost voltage and the relationship can be complex. The
TEA1713 has a soft-start function to ensure that the resonant converter starts or restarts
with safe currents.
The soft-start function forces a start at high frequency so that currents are acceptable in
all conditions. The soft-start 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.