SI9140DQ VISHAY [Vishay Siliconix], SI9140DQ Datasheet - Page 14

• Manufacturer Part Number: SI9140DQ
• Description: MP Controller For High Performance Process Power Supplies
• Manufacturer: VISHAY [Vishay Siliconix]

Si9140
Vishay Siliconix
P
I
P
I
I
DI +
I
P
Inductor
The size and value of the inductor are critical in meeting overall
circuit dimensional requirements and in assuring proper
transient voltage regulation. The size of the core is determined
by the output power, the material of the core, and the operating
frequency. To handle higher output power, the core must be
larger. Luckily, a higher switching frequency will lower the
inductance value, decreasing the core size. However, a higher
switching frequency can also mean greater core loss.
In applications where the dc flux density is high and the ac flux
density swing is only 100 to 200 gauss, the core loss will be
www.vishay.com
14
RMS RECT
RMS SW
PP
PEAK
0 A
Dissipation
Dissipation
IN
Current
= I
+
L
+
PEAK
V
+
O
P
+
f
h
IN
in switch + I
in synchronous rectification + I
OSC
V
+ DI
– (0.5
O
I
O
I
2
PEAK
I
PEAK
I PEAK 2 ) I PP 2 ) I PEAK
V
V
IN
O
2
V
) I
O
RMS SW
PP
DI)
2
) I
2
PEAK
R
SW
I PP
)
I
PP
RMS RECT
Q
SW
(V IN – V
3
3
V
IN
V
V
2
O
2
O
IN
V
)
IN
R
RECT
f
OSC
I
PP
)
)
Q
I
PP
RECT
time
I
R
I
R
Q
Q
V
V
I
f
h
t
RMSSW
RMSRECT
O
OSC
C
SW
RECT
IN
O
SW
RECT
V
I
O
O
V
2
negligible compared to the wire loss. Kool Mu is the best
material to use at 500 kHz to deliver 30 W in the minimum
volume.
frequency, but the core size is fairly large. If the power supply
is designed on the motherboard and space is not a critical
issue, ferrite is a better choice.
The higher switching frequency reduces the core size by
decreasing the amount of energy that must be stored between
switching periods. It also accelerates the transient response to
the load by decreasing the inductance value. The inductance
is calculated with following equation:
2
IN
t
C
f
OSC
=
=
=
=
=
=
=
=
=
=
=
=
f
OSC
Switch rms current
Switch on resistance
Synchronous rectifier rms current
Synchronous rectifier on resistance
Total gate charge of switch
Total gate charge of synchronous rectifier
Input voltage
Output voltage
Output current
Switching frequency
efficiency
Crossover time
Ferrite has a lower core cost and loss at this
S-40699—Rev. H, 19-Apr-04
Document Number: 70026