ISL6580CR Intersil, ISL6580CR Datasheet - Page 21

• 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

All inductors that utilize magnetic material for increased
permeability, have a maximum current level at which the
inductance dramatically falls. This is known as magnetic
saturation. Most inductor vendors will specify the current at
which some percentage of inductance has been lost due to
saturation. It is important to stay well within the limits of the
saturation current of the chosen inductor. It should also be
noted that the saturation current reduces at higher
temperatures.
di/dt vs Loss
Maximizing the delta I within the inductor to improve di/dt has
the effect of increasing peak and RMS currents in the
ISL6580, Power FETs, and the inductor itself. The following
formulas can be used to calculate the effective RMS current
to be used in determining the power loss in these elements:
Operating Frequency
Phase operating frequency has the following relative impacts
on the system performance:
Ipeak
∆I
Ton
1. Size - Higher frequency per phase will minimize the size
2. System Bandwidth – higher switching frequencies allow
3. Power loss – In general power loss increases
4. Hysteresis loss is caused by alternating flux within the
Irms
Irms
Irms
=
of the required output inductor while maintaining a given
delta current in the inductor. Generally speaking ferrites
perform best at higher frequencies (>200kHz). This is
due to the fact that the magnetic materials are higher and
lower conductivity, which tends to reduce eddy current
losses within the core.
higher closed loop unity gain frequencies. This is
because the main limiting factor in compensation of the
voltage loop concerns the Nyquist limitation of the power
stage. The voltage loop must be held less than 1/2 the
channel switching frequency for a single phased system.
Practical designs limit loop bandwidth to < 1/5 of the
phase switching frequency.
logarithmically with phase frequency as it pertains to the
output inductor. Higher frequencies can cause:
core material. Hysteresis loss is a function of the area
enclosed by the BH loop and is due to the energy
required to move magnetic domains. This loss element
decreases logarithmically in most magnetic materials and
=
(
---------------------------------------------
_
_
_
Vin Vout
DTp
=
NFET
ISL
Ind
--------------------- -
Phases
–
,
Iave
6580
Tp
=
L
=
=
=
Irms
)Ton
-- -
F
1
(
+
Ipk
1
-- - ∆I
2
(
Ipk
(
2
_
+
ISL
)where:
2
(
Ipk
+
(
6580
Ipk
)(
D
21
Itr
3
)(
=
3
)
2
Itr
Vout
------------ -
+
+
Vin
Itr
)
Irms
+
2
Itr
)
1 (
2
−
_
)
D
D
NFET
)
2
(EQ. 5)
(EQ. 4)
ISL6580
MOSFET Selection
In the Intersil Digital Multiphase Architecture, a critical
component selection is the low side MOSFET. The power
dissipation from the low and high side MOSFET is
dominated by different factors. Because of the longer duty
cycle (Figure 33), the low side MOSFET efficiency is
dominated by static on losses. However, the low duty cycle
of the high side MOSFET results in the majority of its losses
to come from switching of the FET (Figure 34).
5. Eddy current loss from the circulating currents within the
6. Copper or winding loss. This is also dependent on the
FIGURE 33. HIGH AND LOW SIDE MOSFET DUTY CYCLE
can be a major contributor at higher frequencies. Inductor
vendors work to select materials that suite a specific
frequency range.
magnetic materials. Higher switching frequencies
produce higher eddy current loss. Eddy current loss can
extend to any conductor that is in close proximity to the air
gap of a gapped core inductor. Since field strength tends
to diminish a rate approximately equal to the inverse
square of the distance, conductors should be held to at
least 4x the distance of the air gap itself.
wire size, switching frequency, etc. Skin effect is the
tendency of AC currents to migrate to the outer portions
of a conductor. This can tend to decrease the effective
copper cross sectional area of a conductor at high
frequencies and should be considered in selection of
inductors with relatively thick conductors.