ISL6612A_14 Datasheet, PDF (7/12 Pages) Intersil Corporation – Advanced Synchronous Rectified Buck MOSFET Drivers with Pre-POR OVP

Description
PWM
UGATE
ISL6612A, ISL6613A
t_PDHU
t_RU
1.5V < PWM < 3.2V
t_PDLU
t_FU
t_PDTS
1.0V < PWM <2.6V
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 ISL6612A and
ISL6613A 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 startup;
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.
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
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
7
FN9159.7
May 1, 2012