6
FN9157.6
September 11, 2015
Description
Operation
Designed for versatility and speed, the ISL6594A and
ISL6594B MOSFET drivers 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
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
“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.
Adaptive Zero Shoot-Through Deadtime Control
These drivers incorporate an 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 LGATE voltage is
monitored until it drops below 1.75V, at which time the
UGATE is released to rise after 20ns of propagation delay.
Once the PHASE is high, the 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.
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
thresholds outlined in the “Electrical Specifications” on
page 4 determine when the lower and upper gates are
enabled.
This feature helps prevent a negative transient on the output
voltage when the output is shut down, eliminating the
Schottky diode that is used in some systems for protecting
the load from reversed output voltage events.
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
ISL6594A, ISL6594B
