ISL6580CR Intersil, ISL6580CR Datasheet - Page 24

• Manufacturer Part Number: ISL6580CR
• Description: IC DRIVER HIGH SIDE FET 56-QFN
• Manufacturer: Intersil
• Type: High Side/Low Side Driverr

Specifications of ISL6580CR

• Input Type: Non-Inverting
• Number Of Outputs: 12
• On-state Resistance: 20 mOhm
• Current - Output / Channel: 25A
• Current - Peak Output: 35A
• Voltage - Supply: 5 V ~ 12 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 56-VQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

heat flux designed into the system is die and heat sink size.
The larger the die size, the higher the part costs but more
effective heat flux occurs. A smaller die size can be used
with a larger heat sink added. Of course increasing the
switching speed of the device and/or reducing the frequency
of operation of the transistor will reduce power dissipation,
but both of these are typically defined directly from the
application.
If there is a high thermal increase in a MOSFET, a cost
analysis should be performed to consider a larger die size, a
larger heat sink, or parallel MOSFETs to share the current.
MOSFET Transistor Selection
When selecting the appropriate low side MOSFET to put in
the power circuitry, there are some basic characteristics that
need to be considered.
• N type or P type MOSFET
• For the low side MOSFET component, an N polarity
• Current Rating
• At least 3X the peak current input should be select for the
• Voltage Rating
The input voltage for computing multiphase power supply for
the chip set is a 12V DC nominal. Standard MOSFET
voltage rating for the low side FET ranges between 20V-30V
depending on the switching speed of the switch node and
the noise of the input rail. This increased voltage level is
used to take into account inductive voltage kickback and
transient voltage inputs.
Inductive Switching
The ISL6580 Integrated Power Stage is a High Side
FET/driver combination with external synchronous rectifier
that provides high current at high switching frequency.
Schematic of Figure 38 shows a typical synchronous buck
converter application using the ISL6580.
FIGURE 38. SYNCHRONOUS BUCK CONVERTER USING
MOSFET is always used.
current rating.
ISL6580
24
ISL6580
Package and board level interconnects of individual
components in the high current loops give rise to series RLC
circuits. Fast switching of large currents in these loops will
generate large voltage transients that may exceed maximum
device ratings. Specifically, at the turn off phase of the high
side switch, the sudden disruption in the loop current will
generate fast transient ringing at the high side switch
exposing the high side switch to large voltages that can
exceed the rated break down voltage for that device. Figure
39 shows the high frequency equivalent circuit at the turn-off
of the high side switch before the turn-on of the low side
switch. Included in this schematic are the relevant parasitic
effects of various components and interconnects.
This application note discusses the use of external Schottky
diodes in order to limit the amplitude of transient voltage spikes
across the drain to source of the high side switch device.
Clamping Using Schottky Diodes
The simplest approach to protect the High Side FET from
inductive switching is to limit loop inductance. This can be
achieved by proper layout of the high current loops and
careful selection of the components in this loop. The goal is
to minimize overall loop inductance. This inductance
includes HSFET bonding inductance, the external NFET
inductance, the power supply decoupling capacitance’s ESL,
and interconnect inductances between these components.
While good layout of the PCB must be always practiced,
component selection is often compromised by other factors
such as pricing or physical dimensions. For example it is
possible that a single NFET with an inductance of up to 8nH
is selected for the low side switch.
In such situations where a high inductance FET or special
layout considerations result in large loop inductance, placement
of a Schottky diode from the switch node to ground will clamp
the negative ringing and limit the voltage across drain to source
V
V
FIGURE 39. HIGH FREQUENCY EQUIVALENT CIRCUIT OF
S U P P
S U P P
E S R
E S R
E S L
E S L
L
L
THE HIGH SIDE SWITCH TURN OFF LOOP
i1
i1
L
L
i 4
i 4
R
R
i 1
i 1
R
R
i4
i4
C
C
C
C
C
C
C
C
C
C
C
C
C
C
g s
g s
g s
g s
g d
g d
g d
g d
g s
g s
g s
g d
g d
g d
L
L
L
R
R
R
R
R
L
L
R
R
L
L
L
L
L
R
R
R
P
P
P
P
P
P
i 2
i 2
i 2
i 2
i 3
i 3
i 3
i 3
N
N
N
N
N
N
C
C
C
C
C
C
C
d s
d s
d s
d s
d s
d s
d s
I
I
I
L
L
L