ISL6594D_14 Datasheet, PDF (6/11 Pages) Intersil Corporation – Advanced Synchronous Rectified Buck MOSFET Drivers with Protection Features

Description
PWM
UGATE
t_PDHU
t_RU
ISL6594D
1.18V < PWM < 2.36V
t_PDLU
t_FU
t_PDTS
0.76V < PWM < 1.96V
t_TSSHD
t_PDTS
LGATE
t_PDLL
t_FL
t_RL
t_PDHL
t_TSSHD
FIGURE 1. TIMING DIAGRAM
Operation
Designed for versatility and speed, the ISL6594D MOSFET
driver controls 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
start-up; 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” on page 4), the PWM signal takes
control of gate transitions. A rising edge on PWM initiates
the turn-off of the lower MOSFET (see Timing Diagram on
page 6). After a short propagation delay [t_PDLL], the lower
gate begins to fall. Typical fall times [t_FL] are provided in the
“Electrical Specifications” on page 4. 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 ISL6594D 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 hold-off 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
6
FN9282.1
December 3, 2007