ISL6210 Datasheet, PDF (6/10 Pages) Intersil Corporation – Dual Synchronous Rectified MOSFET Drivers

Timing Diagram
PWM
t_PDHU
t_PDLU
t_RU
UGATE
LGATE
1V
t_PDLL
ISL6210
2.5V
1V
t_TSSHD
t_RU
t_PTS
t_RL
t_PDHL
t_TSSHD
t_FL
FIGURE 1. TIMING DIAGRAM
t_FU
t_PTS
Description
Theory of Operation
Designed for speed, the ISL6210 dual MOSFET driver
controls both high-side and low-side N-Channel FETs for two
separate channels of a Multiphase PWM system from two
independent PWM signals.
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. When LGATE has fallen below 1V, UGATE is
allowed to turn ON. This prevents both the lower and upper
MOSFETs from conducting simultaneously, or shoot-
through.
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_PDLU] is encountered before the upper
gate begins to fall [t_FU]. 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_RL], turning on the lower
MOSFET.
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 0.5Ω 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.
Diode Emulation
Diode emulation allows for higher converter efficiency under
light-load situations. With diode emulation active, the
ISL6210 will detect the zero current crossing of the output
inductor and turn off LGATE. This ensures that
discontinuous conduction mode (DCM) is achieved. Diode
emulation is asynchronous to the PWM signal. Therefore,
the ISL6210 will respond to the FCCM input immediately
after it changes state.
NOTE: Intersil does not recommend Diode Emulation use with
r_DS(ON) current sensing topologies. The turn-OFF of the low side
MOSFET can cause gross current measurement inaccuracies.
Three-State PWM Input
A unique feature of the ISL6210 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.
Adaptive Shoot-Through Protection
Both drivers incorporate adaptive shoot-through protection
to prevent upper and lower MOSFETs from conducting
simultaneously and shorting the input supply. This is
accomplished by ensuring the falling gate has turned off one
MOSFET before the other is allowed to turn on.
6
FN6392.0
November 28, 2006