ISL6209 Datasheet, PDF (6/10 Pages) Intersil Corporation – High Voltage Synchronous Rectified Buck MOSFET Driver

ISL6209
PWM
UGATE
LGATE
t_PDLLGATE
t_PDHUGATE
t_RUGATE
t_PDLUGATE
t_FUGATE
1V
1V
t_FLGATE
t_PDHLGATE
FIGURE 3. TIMING DIAGRAM
t_RLGATE
A falling transition on PWM indicates the turn-off of the upper
MOSFET and the turn-on of the lower MOSFET. A short
propagation delay [t_PDLUGATE] is encountered before the
upper gate begins to fall [t_FUGATE]. Again, the adaptive
shoot-through circuitry determines the lower gate delay time
t_PDHLGATE. The upper MOSFET gate-to-source voltage is
monitored, and the lower gate is allowed to rise, after the
upper MOSFET gate-to-source voltage drops below 1V. The
lower gate then rises [t_RLGATE], turning on the lower
MOSFET.
This driver is optimized for converters with large step down
ratio, such as those used in a mobile-computer core voltage
regulator. The lower MOSFET is usually sized much
larger.Timing Diagram
This driver is optimized for converters with large step down
compared to the upper MOSFET because the lower
MOSFET conducts for a much longer time in a switching
period. The lower gate driver is therefore sized much larger
to meet this application requirement. The 0.4Ω on-resistance
and 4A sink current capability enable the lower gate driver to
absorb the current injected to the lower gate through the
drain-to-gate capacitor of the lower MOSFET and prevent a
shoot through caused by the high dv/dt of the phase node.
Three-State PWM Input
A unique feature of the ISL6209 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 output drivers 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.
During start-up, PWM should be in the three-state position
(1/2 V_CC) until actively driven by the controller IC.
Shoot-Through Protection
The ISL6209 driver delivers shoot-through protection by
incorporating gate threshold monitoring and programmable
dead-time to prevent upper and lower MOSFETs from
conducting simultaneously, thereby shorting the input supply
to ground. Gate threshold monitoring ensures that one gate
is OFF before the other is allowed to turn ON.
During turn-off of the lower MOSFET, the LGATE voltage is
monitored until it reaches a 1V threshold, at which time the
UGATE is released to rise. Internal circuitry monitors the
upper MOSFET gate-to-source voltage during UGATE
turn-off. Once the upper MOSFET gate-to-source voltage
has dropped below a threshold of 1V, the LGATE is allowed
to rise.
In addition to gate threshold monitoring, a programmable
delay between MOSFET switching can be accomplished by
placing a resistor from the DELAY pin to ground. This delay
allows for maximum design flexibility over MOSFET
selection. The delay can be programmed from 5ns to 50ns. If
not desired, the DELAY pin must be tied to VCC to disable
the delay circuitry. Gate threshold monitoring is not affected
by the addition or removal of the additional dead-time. Refer
to Figure 4 and Figure 5 for more detail.
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