AN10907
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© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
20 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
The shape of the current from SUPREG at switch on is related to:
•
the supply voltage for the internal driver (10.9 V)
•
the characteristic of the internal driver
•
the gate capacitance to be charged
•
the gate threshold voltage for the MOSFET to switch on
•
the external circuit to the gate
The charging of SUPHS for GATEHS is synchronized in time with GATELS but has a
different shape because of the bootstrap function.
6.5.4 Supply voltage for the output drivers: SUPHS
The high-side driver is supplied by an external bootstrap buffer capacitor. The bootstrap
capacitor is connected between the high-side reference pin HB and the high-side driver
supply input pin SUPHS. This capacitor is charged by an external diode from SUPREG
during the time that HB is low. With the use of a suitable external diode, the voltage drop
between SUPREG and SUPHS can be minimized. This is especially important when
using a MOSFET that needs a large amount of gate charge and/or when switching at high
frequencies.
Instead of using SUPREG as the power source for charging SUPHS, another supply
source can be used. In such a construction it is important to check for correct start/stop
sequences and to prevent the voltage exceeding the maximum value of HB +14 V.
Note that for each cycle, the current taken from SUPREG to charge SUPHS differs (in
time and shape) from the current taken by GATELS.
6.5.4.1
Initial charging of SUPHS
At start-up, SUPHS is charged by the bootstrap function by setting GATELS HIGH to
switch on the low-side MOSFET, keeping the HB node at low voltage. The PFC operation
is started while SUPHS is being charged. The time between start charging and start HBC
operation is normally sufficient to charge SUPHS completely.
6.5.4.2
Current load on SUPHS
The current taken from SUPHS consists of two parts:
•
Internal MOSFET driver GATEHS
•
Internal circuit to control GATEHS (37
A)
It can be seen from
that the current taken by the driver GATEHS occurs at
switch on. The shape of the current from SUPHS at switch on is related to:
•
the value of the supply voltage for the internal driver
•
the characteristic of the internal driver
•
the gate capacitance to be charged
•
the gate threshold voltage for the MOSFET to switch on
•
the external circuit to the gate
The voltage value of SUPHS can vary.
