zl2006 Intersil Corporation, zl2006 Datasheet - Page 21

• Manufacturer Part Number: zl2006
• Description: Adaptive Digital Dc-dc Controller With Drivers And Current Sharing
• Manufacturer: Intersil Corporation

Table 17. Power Supply Requirements
5.8.1
The design of the buck power stage requires several
compromises among size, efficiency, and cost. The
inductor core loss increases with frequency, so there is
a trade-off between a small output filter made possible
by a higher switching frequency and getting better
power supply efficiency. Size can be decreased by
increasing the switching frequency at the expense of
efficiency. Cost can be minimized by using through-
hole
components are physically large.
To start the design, select a switching frequency based
on Table 18. This frequency is a starting point and may
be adjusted as the design progresses.
Table 18. Circuit Design Considerations
Frequency Range
Input voltage (V
Output voltage (V
Output current (I
Output voltage ripple
(V
Output load step (I
Output load step rate
Output deviation due to load
step
Maximum PCB temp.
Desired efficiency
Other considerations
orip
200–400 kHz
400–800 kHz
)
800 kHz –
1.4 MHz
inductors
Design Goal Trade-offs
Parameter
IN
OUT
)
OUT
ostep
)
)
)
and
21
capacitors;
Efficiency
Moderate
Highest
Lower
< 3% of V
3.0 – 14.0 V
0.6 – 5.0 V
0 to ~25 A
Various
Range
120°C
< Io
—
—
—
OUT
however
Circuit Size
Optimize for
Smallest
1% of V
Smaller
small size
Example
50% of I
Larger
± 50 mV
10 A/µS
Value
1.2 V
85°C
12 V
20 A
85%
these
OUT
o
ZL2006
5.8.2
The output inductor selection process must include
several trade-offs. A high inductance value will result
in a low ripple current (I
capacitance and produce a low output ripple voltage,
but may also compromise output transient load
performance. Therefore, a balance must be struck
between output ripple and optimal load transient
performance. A good starting point is to select the
output inductor ripple equal to the expected load
transient step magnitude (I
Now the output inductance can be calculated using the
following equation, where V
voltage:
The average inductor current is equal to the maximum
output current. The peak inductor current (I
calculated using the following equation where I
the maximum output current:
Select an inductor rated for the average DC current
with a peak current rating above the peak current
computed above.
In over-current or short-circuit conditions, the inductor
may have currents greater than 2X the normal
maximum rated output current. It is desirable to use an
inductor that still provides some inductance to protect
the load and the MOSFETs from damaging currents in
this situation.
Once an inductor is selected, the DCR and core losses
in the inductor are calculated. Use the DCR specified
in the inductor manufacturer’s datasheet.
Inductor Selection
L
OUT
I
Lpk
=
V
I
=
opp
OUT
opp
I
OUT
ostep
=
fsw
×
), which will reduce output
I
INM
⎛
⎜ ⎜
⎝
):
ostep
1
+
×
−
is the maximum input
I
I
opp
opp
V
V
2
December 15, 2010
OUT
INM
⎞
⎟ ⎟
⎠
FN6850.1
Lpk
OUT
) is
is