ISL6615A Datasheet, PDF (6/12 Pages) Intersil Corporation – High-Frequency 6A Sink Synchronous MOSFET Drivers with Protection Features

Description
PWM
UGATE
t_PDHU
t_RU
ISL6615A
1.18V < PWM < 2.36V
t_PDLU
t_FU
t_PDTS
0.76V < PWM < 1.96V
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 ISL6615A
MOSFET driver controls 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 the “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 the following section titled “Advanced
Adaptive Zero Shoot-Through Dead-Time Control” for
details). The lower gate then rises [t_RL], turning on the
lower MOSFET.
Advanced Adaptive Zero Shoot-Through
Dead-time Control
The ISL6615A driver incorporates a unique adaptive
dead-time control technique to minimize dead-time,
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 the 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. Prior to reaching
this level, there is a 25ns blanking period to protect
against sudden dips in the LGATE voltage. Once 1.75V is
reached, 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 PWM falling edge and subsequent UGATE
turn-off. If PHASE falls to less than +0.8V, the LGATE is
released to turn on after 10ns of propogation delay. If the
UGATE-PHASE falls to less than 1.75V and after 40ns of
propogation delay, LGATE is released to rise.
Tri-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 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.
6
FN6608.1
April 22, 2010