gate to source voltage of the High Side MOSFET is also
monitored. When VGS(High Side) is discharged below
1V, a threshold known to turn High Side MOSFET off, a
secondary delay is initiated, which results in Low Side
being gated “ON” regardless of the state of the “VSWH”
pin. This way it will be ensured that the converter can
sink current efficiently and the bootstrap capacitor will be
refreshed appropriately during each switching cycle.
Mode of operation
The PX3516 functionality is enabled by the VCC pin.
When the VCC pin voltage overcomes the VCC rising
voltage threshold the driver begins to operate depending
on the PWM status. Before the VCC voltage reaches the
VCC rising threshold both MOSFET are kept in OFF
state. For VCC is recommended to have a slope for the
rising edge higher then 5V/50ms. On the PVCC pin no
UVLO function is implemented.
During the start up depending on several factors it can
be that the power input for the conversion (12V) rise
before the 5V input. In this case it could happen that the
high side has an induced turn on. In order to avoid this
undesirable effect the PX3516 embeds a resistance of
500 kOhm between UGATE pin and PHASE pin.
The VCC (as well the PVCC) can range between 4.5V
and 6.5V; this gives the flexibility to work with the 5V bus
or in case optimize the efficiency choosing a different
driving voltage.
Current capability and Internal
Bootstrap
The PX3516 functionality is driven by the PWM signal
transitions. When the PWM signal performs a transition
between low state to high state (PWM voltage higher
than 2.4V) the Low Side MOSFET is turned off, after the
turn off delay propagation time. Then the High Side
MOSFET is turned on, after the turn on propagation
delay time. Once the on time is expired the PWM signal
provides a transition between the high states to the low
state (PWM voltage lower than 1V). This will drive the
High Side MOSFET from the ON state to the OFF state,
after the turn off propagation delay time. The PX3516 is
also capable to drive the two external MOSFET both in
off state. When the PWM signal enters in the shut down
window or 3-state (typically between 1.37V and 1.77V)
after the shut down hold off time both MOSFET are
switched off. This feature is useful when the IC controller
wants to reduce the number of active phases in order to
reduce the power consumption. In principle the 3-state
status can be used also to improve the transition
between high loads to low load.
The PX3516 implements high current capability and low
ohmic pull down resistances for the driving stages. The
high current capability ensures fast switching transition
for the MOSFET in order to reduce the switching losses
(2A of driving source/sink current for the upper
MOSFET) even with high gate charge high side. The low
ohmic pull down resistance (Low driver sink impedance
0.5 Ohm) is mainly important to avoid the induced turn
on phenomenon on the low side during the fast turn on
of the high side MOSFET.
The high side is powered through the bootstrap circuitry
The PX3516 provides embedded bootstrap diode, so to
complete the power network only a capacitance between
PHASE and BOOT is needed. In many cases the
PX3516 is optimized for the best switching behavior so
an external resistance is not needed. The bootstrap
capacitance is chosen depending on the high side gate
charge. The following formula is giving a good
The PX3516 implements an embedded resistors
network, which forces the PWM pin of the device in the
middle of the shut down window, if the PWM input is left
floating from the controller.
estimation of the voltage drop across the bootstrap
capacitance due to the charging of the high side:
CBOOT>QGATE/
∆VBOOT
In order to avoid cross conduction between the High
Side MOSFET and the Low Side MOSFET an anti-
shoot-through control is implemented with the adaptive
scheme. The adaptive scheme is implemented in order
to use a variety of different power MOSFET for different
kind of conversion. Nevertheless the dead time is kept
as short as possible in order to increase the efficiency of
the overall solution.
Where the VBOOT is the desired variation of the
∆
bootstrap voltage.
The low side driver is powered through the PVCC pin.
Same considerations and formula done for the bootstrap
capacitance can be done for the capacitance used to
filter the PVCC pin.
The driver includes gate drive functionality to protect
against shoot through. In order to protect the power
stage from overlap, both High Side and Low Side
MOSFET being on at the same time, the adaptive
control circuitry monitors the voltage at the “PHASE” pin.
When the PWM signal goes low, the High Side MOSFET
will begin to turn off. Once the “PHASE” pin falls below
1V, the Low Side MOSFET is gated on. Additionally, the
The driving stage of the PX3516 is optimized for the 5V
driving voltage. This design makes the PX3516 driver
more suitable than other variable driving voltage drivers
optimized for 10V – 12V range. In this case superior
performance are expected using an optimized 5V driver
at 6V of driving voltage compared to a optimized 12V
driver used at the same driving voltage.
PX3516
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