MBRS130 データシートの表示（PDF） - Exar Corporation
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MBRS130 Datasheet PDF : 12 Pages
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XRP7 6 7 5
3 A 1 8 V Sy n ch r on ou s PFM/ PW M St ep - Dow n Reg u lat or
APPLICATION INFORMAT ION
SETTING THE OUTPUT V OLTAGE
Use an external resistor divider to se t the
output voltage. Program the output voltage
from:
ܴͳൌܴʹൈ൬Ͳܸ Ǥͻைʹ்ܸͷെͳ൰
VOUT(V)
3.3
2.5
1.8
1.5
1.2
Ʃ,L(p - p) (A)
L(µH)
Inductor
Example
0.7
4.9
744314 490
0.8
4.9
744314 490
0.7
4.9
744314 490
0.6
4.9
744314 490
0.5
4.9
744314 490
Table 2: Suggested inductor values
for VIN=5V and IOUT=3 A
Where:
R1 is the resistor between V OUT and FB
R2 is the resistor between FB and GND
QRPLQDOO\N
0.925V is the nominal feedback voltage .
OUTPUT INDUCTOR
Select the output inductor for inductance L, DC
current rating I DC and saturation current rating
I SAT. I DC should be larger than regulator output
current. I SAT, as a rule of thumb, should be
50% higher than the regulator output current.
Since the regulator is rated at 2A th
en I DC$
and I SAT$Calculate the inductance from:
ܮൌሺܸூேെܸை்ሻ൬߂ܫൈܸை݂௦ൈ்ܸூே൰
Where:
OUTPUT CAPACITOR COUT
Select the output capacitor for voltage rating,
capacitance C OUT and Equivalent Series
Resistance ESR . The voltage rating, as a rule
of thumb, should be at least twice the output
voltage. When calculating
the required
capacitance, usually the overriding
requirement is current load - step transient. If
the unloading transient (i.e., when load
transitions from a high to a low current ) is
met, then usually the loading transient (when
load transitions from a low to a high
current )
is met as well. Therefore c alculate the C OUT
based on the unload ing transient requirement
from:
ܥை்ൌܮൈቆሺܸை்ܫுܸ௧ଶെܫ௦ሻଶ௪ଶെܸ௧ை்ଶቇ
Where:
Ʃ,L is peak - to - peak inductor current ripple
nominally set to 30% - 40% of I OUT
fS is nominal switching frequency (340kHz)
As an example , inductor values for several
common output voltages are shown in table
s1
and 2 .
L is the inductance calculated in the preceding
step
I High is the value of load - step prior to
unloading. This is nominally set equal to
regulator current rating ( 3A).
I Low is the value of load - step after unloading.
This is nominally set equal to 50% of regulator
current rating ( 1.5 A).
VOUT(V)
5.0
3.3
2.5
1.8
1.5
1.2
Ʃ,L( p - p ) (A)
L( µ H)
Inductor
Example
0.9
10
744314101
0.7
10
744314101
0.6
10
744314101
0.6
7.6
744314 760
0.5
7.6
744314 760
0.6
4.9
744314 490
Table 1: Suggested inductor values
for VIN=12V and IOUT= 3A
Vtransient is the maximum permissible voltage
transient corresponding to the load step
mentioned above. V transient is typically specified
fr om 3% to 5% of VOUT.
ESR of the capacitor ha s to be selected such
that the output voltage ripple requirement
Ʃ9OUT, nominally 1% of V OUT, is met. Voltage
ripple Ʃ9OUT is mainly composed of t wo
components : the resistive ripple due to ESR
and capacitive ripple due to
COUT charge
transfer. For applications requiring low
voltage
ripple , ceramic capacitors are recommended
© 2013 Exar Corporation
8/ 12
Rev. 1.0.0
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