ADP3160 Ver la hoja de datos (PDF) - Analog Devices
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ADP3160 Datasheet PDF : 16 Pages
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ADP3160/ADP3167
270F ؋ 4
VIN
OS-CON 16V
12V
C11
C12
C13
VIN RTN
RA
26.1k⍀
FROM
CPU
COC
3.3nF
RB
11.0k⍀
U1
ADP3160
1 VID4
VCC 16
2 VID3
REF 15
3 VID2
CS– 14
4 VID1 PWM1 13
5 VID0 PWM2 12
6 COMP CS+ 11
7 FB PWRGD 10
8 CT
GND 9
C1
150pF
C2
100pF
R1
1k⍀
C14
R6
10⍀
C4
4.7F
C25 1nF
R7
20⍀
R4
4m⍀
C23
15nF
C26
D1
C9
4.7F
R5
MBR052LTI
1F
2.4k⍀
Z1
ZMM5236BCT
Q5
2N3904
U2
ADP3414
1 BST DRVH 8
2 IN
SW 7
3 NC PGND 6
4 VCC DRVL 5
C5
1F
Q1
FDB7030L L1
600nH
Q2
FDB8030L
D2
C10
MBR052LTI
1F
U3
ADP3414
1 BST DRVH 8
2 IN
SW 7
3 NC PGND 6
4 VCC DRVL 5
C6
1F
2200F ؋ 9
Q3
FDB7030L L2
RUBYCON MBZ 6.3V
13m⍀ ESR (EACH)
600nH
C23
Q4
FDB8030L
C15 C16 C17 C18 C19 C20 C21 C22
VCC(CORE)
1.1V – 1.85V
53.4A
VCC(CORE) RTN
NC = NO CONNECT
Figure 6. 53.4 A Intel CPU Supply Circuit, VRM 9.0 FMB Design
CT Selection—Choosing the Clock Frequency
The ADP3160 and ADP3167 use a fixed-frequency control archi-
tecture. The frequency is set by an external timing capacitor, CT.
The value of CT for a given clock frequency can be selected using
the graph in Figure 2.
The clock frequency determines the switching frequency, which
relates directly to switching losses and the sizes of the inductors
and input and output capacitors. A clock frequency of 400 kHz
sets the switching frequency of each phase, fSW, to 200 kHz, which
represents a practical trade-off between the switching losses and
the sizes of the output filter components. From Figure 2, for 400 kHz
the required timing capacitor value is 150 pF. For good frequency
stability and initial accuracy, it is recommended to use a capacitor
with a low temperature coefficient and tight tolerance, e.g., an
MLC capacitor with NPO dielectric and with 5% or less tolerance.
Inductance Selection
The choice of inductance determines the ripple current in the
inductor. Less inductance leads to more ripple current, which
increases the output ripple voltage and the conduction losses in
the MOSFETs, but allows using smaller size inductors and, for
a specified peak-to-peak transient deviation, output capacitors
with less total capacitance. Conversely, a higher inductance
means lower ripple current and reduced conduction losses,
but requires larger size inductors and more output capacitance
for the same peak-to-peak transient deviation. In a 2-phase
converter a practical value for the peak-to-peak inductor ripple
current is under 50% of the dc current in the same inductor.
A choice of 46% for this particular design example yields a total
peak-to-peak output ripple current of 23% of the total dc output
current. The following equation shows the relationship between
the inductance, oscillator frequency, peak-to-peak ripple current
in an inductor, and input and output voltages.
L
=
(VIN
VIN ¥
–VAVG ) ¥VAVG
fSW ¥ IL(RIPPLE )
(1)
For 12.5 A peak-to-peak ripple current, which corresponds to
just under 50% of the 26.7 A full-load dc current in an induc-
tor, Equation 1 yields an inductance of:
L
=
(12 V – 1.635V ) ¥ 1.635V
12 V ¥ 400 kHz/ 2 ¥ 12.5 A
= 565 nH
A 600 nH inductor can be used, which gives a calculated ripple
current of 12.2 A at no load. The inductor should not saturate
at the peak current of 32.8 A and should be able to handle the
sum of the power dissipation caused by the average current of
26.7 A in the winding and the core loss.
The output ripple current is smaller than the inductor ripple
current due to the two phases partially canceling. This can be
calculated as follows:
IOD
=
2 ¥VAVG (VIN – 2 ¥VAVG )
VIN ¥ L ¥ fOSC
=
(2)
2
¥ 1.635V(12V – 2 ¥ 1.635V
12V ¥ 600 nH ¥ 400 kHz
)
=
9.9
A
Designing an Inductor
Once the inductance is known, the next step is either to design
an inductor or find a standard inductor that comes as close as
possible to meeting the overall design goals. The first decision in
designing the inductor is to choose the core material. There are
several possibilities for providing low core loss at high frequen-
cies. Two examples are the powder cores (e.g., Kool-Mm® from
Magnetics) and the gapped soft ferrite cores (e.g., 3F3 or 3F4
from Philips). Low-frequency powdered iron cores should be
avoided due to their high core loss, especially when the inductor
value is relatively low and the ripple current is high.
–8–
REV. B
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