6
FN6463.0
February 26, 2007
Description
Operation
Designed for versatility and speed, the PX3511D MOSFET
driver control both high-side and low-side N-Channel FETs
of a half-bridge power train from one externally provided
PWM signal.
Prior to VCC exceeding its POR level, the Pre-POR
overvoltage protection function is activated during initial
startup; the upper gate (UGATE) is held low and the lower
gate (LGATE), controlled by the Pre-POR overvoltage
protection circuits, is connected to the PHASE. Once the
VCC voltage surpasses the VCC Rising Threshold (See
Electrical Specifications), the PWM signal takes control of
gate transitions. A rising edge on PWM initiates the turn-off
of the lower MOSFET (see Timing Diagram). After a short
propagation delay [t
PDLL
], the lower gate begins to fall.
Typical fall times [t
FL
] are provided in the Electrical
Specifications section. Adaptive shoot-through circuitry
monitors the LGATE voltage and determines the upper gate
delay time [t
PDHU
]. This prevents both the lower and upper
MOSFETs from conducting simultaneously. Once this delay
period is complete, the upper gate drive begins to rise [t
RU
]
and the upper MOSFET turns on.
A falling transition on PWM results in the turn-off of the
upper MOSFET and the turn-on of the lower MOSFET. A
short propagation delay [t
PDLU
] is encountered before the
upper gate begins to fall [t
FU
]. Again, the adaptive shoot-
through circuitry determines the lower gate delay time,
t
PDHL
. The PHASE voltage and the UGATE voltage are
monitored, and the lower gate is allowed to rise after PHASE
drops below a level or the voltage of UGATE to PHASE
reaches a level depending upon the current direction (See
next section for details). The lower gate then rises [t
RL
],
turning on the lower MOSFET.
Advanced Adaptive Zero Shoot-Through Deadtime
Control (Patent Pending)
The PX3511D driver incorporates a unique adaptive
deadtime control technique to minimize deadtime, resulting
in high efficiency from the reduced freewheeling time of the
lower MOSFETs’ body-diode conduction, and to prevent the
upper and lower MOSFETs from conducting simultaneously.
This is accomplished by ensuring either rising gate turns on
its MOSFET with minimum and sufficient delay after the
other has turned off.
During turn-off of the lower MOSFET, the PHASE voltage is
monitored until it reaches a -0.2V/+0.8V trip point within
15ns for a forward/reverse current, at which time the UGATE
turns on after 10ns propagation delay. An auto-zero
comparator is used to correct the r
DS(ON)
drop in the phase
voltage preventing from false detection of the -0.2V phase
level during r
DS(ON
conduction period. In the case of zero
current and/or 15ns phase detect expired, the UGATE turns
on after 10ns propagation delay. During the phase detection,
the disturbance of LGATE’s falling transition on the PHASE
node is blanked out to prevent falsely tripping. Once the
PHASE is high, the advanced adaptive shoot-through
circuitry monitors the PHASE and UGATE voltages during a
PWM falling edge and the subsequent UGATE turn-off. If
either the UGATE falls to less than 1.75V above the PHASE
or the PHASE falls to less than +0.8V, the LGATE is
released to turn on after 10ns propagation delay.
Three-State PWM Input
A unique feature of these drivers and other Intersil drivers is
the addition of a shutdown window to the PWM input. If the
PWM signal enters and remains within the shutdown window
for a set holdoff time, the driver outputs are disabled and
both MOSFET gates are pulled and held low. The shutdown
state is removed when the PWM signal moves outside the
shutdown window. Otherwise, the PWM rising and falling
PWM
UGATE
LGATE
t
FL
t
PDHU
t
PDLL
t
RL
t
TSSHD
t
PDTS
t
PDTS
1.18V<PWM<2.36V
0.76V<PWM<1.96V
t
FU
t
RU
t
PDLU
t
PDHL
t
TSSHD
FIGURE 1. TIMING DIAGRAM
PX3511D
