ISL6614
Description
1.5V<PWM<3.2V
PWM
1.0V<PWM<2.6V
t
PDHU
t
PDLU
t
PDTS
t
TSSHD
t
PDTS
UGATE
t
RU
t
FU
LGATE
t
FL
t
PDLL
t
PDHL
t
RL
t
TSSHD
FIGURE 1. TIMING DIAGRAM
Operation
Designed for versatility and speed, the ISL6614 MOSFET
driver controls both high-side and low-side N-Channel FETs
of two half-bridge power trains from two externally provided
PWM signals.
Prior to VCC exceeding its POR level, the Pre-POR
overvoltage protection function is activated; 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 PHASE 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.
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 for a
forward/reverse current, at which time the UGATE is released
to rise. 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, the UGATE is released after 35ns delay of the
LGATE dropping below 0.5V. 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.
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
thresholds outlined in the ELECTRICAL SPECIFICATIONS
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.
Advanced Adaptive Zero Shoot-Through Deadtime
Control (Patent Pending)
These drivers incorporate a unique adaptive deadtime control
technique to minimize deadtime, resulting in high efficiency
8
FN9155.4
July 25, 2005
INTERSIL [ INTERSIL CORPORATION ]
