XRP7675EVB Exar, XRP7675EVB Datasheet - Page 8

• Manufacturer Part Number: XRP7675EVB
• Description: Power Management IC Development Tools 3A 18V PFM/PWM EVAL Board
• Manufacturer: Exar
• Type: DC/DC Converters, Regulators & Controllersr

Specifications of XRP7675EVB

• Product: Evaluation Boards
• Tool Is For Evaluation Of: XRP7675
• Input Voltage: 4.5 V to 18 V
• Output Voltage: 0.925 V to 16 V
• Description/function: Evaluation board for the XRP7675
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Output Current: 3
• For Use With: XRP7675

APPLICATION INFORMATION
SETTING THE OUTPUT VOLTAGE
Use an external resistor divider to set the
output voltage. Program the output voltage
from:
Where:
R1 is the resistor between V
R2 is the resistor between FB and GND
(nominally 10kΩ)
0.925V is the nominal feedback voltage.
OUTPUT INDUCTOR
Select the output inductor for inductance L, DC
current rating I
I
current. I
50% higher than the regulator output current.
Since the regulator is rated at 2A then I
and I
Where:
ΔI
nominally set to 30%-40% of I
f
As an example, inductor values for several
common output voltages are shown in tables 1
and 2.
© 2013 Exar Corporation
VOUT(V) ΔI
S
SAT
L
is nominal switching frequency (340kHz)
5.0
3.3
2.5
1.8
1.5
1.2
. I
is peak-to-peak inductor current ripple
SAT
DC
≥3A. Calculate the inductance from:
should be larger than regulator output
Table 1: Suggested inductor values
SAT
L(p-p)
, as a rule of thumb, should be
for VIN=12V and IOUT=3A
0.9
0.7
0.6
0.6
0.5
0.6
DC
(A)
and saturation current rating
L(µH)
7.6
7.6
4.9
10
10
10
3
3
OUT
A
A
OUT
and FB
1
1
8
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8
Inductor
Example
V
V
S
S
y
y
DC
n
n
≥2A
c
c
h
h
r
r
o
o
8/12
n
n
o
o
u
u
OUTPUT CAPACITOR C
Select the output capacitor for voltage rating,
capacitance
Resistance ESR. The voltage rating, as a rule
of thumb, should be at least twice the output
voltage.
capacitance,
requirement is current load-step transient. If
the
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 calculate the C
based on the unloading transient requirement
from:
Where:
L is the inductance calculated in the preceding
step
I
unloading. This is nominally set equal to
regulator current rating (3A).
I
This is nominally set equal to 50% of regulator
current rating (1.5A).
V
transient
mentioned above. V
from 3% to 5% of V
ESR of the capacitor has to be selected such
that the output voltage ripple requirement
ΔV
ripple ΔV
components: the resistive ripple due to ESR
and capacitive ripple due to C
transfer. For applications requiring low voltage
ripple, ceramic capacitors are recommended
VOUT(V) ΔI
High
Low
transient
s
s
OUT
3.3
2.5
1.8
1.5
1.2
P
P
is the value of load-step after unloading.
unloading
F
, nominally 1% of V
F
is
M
M
is the maximum permissible voltage
/
/
Table 2: Suggested inductor values
the
OUT
P
When
P
corresponding
L(p-p)
W
W
0.7
0.8
0.7
0.6
0.5
for VIN=5V and IOUT=3A
C
value
is mainly composed of two
M
M
(A)
OUT
usually
transient
S
S
calculating
t
t
transient
OUT
e
e
and
L(µH)
OUT
of
p
p
.
4.9
4.9
4.9
4.9
4.9
-
-
D
D
load-step
OUT
is typically specified
to
o
o
Equivalent
(i.e.,
the
w
w
, is met. Voltage
the
n
n
the
X
X
R
R
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Inductor
Example
R
R
when
OUT
e
e
load
overriding
P
P
g
g
Rev. 1.0.0
prior
required
u
u
7
7
charge
l
l
Series
6
6
a
a
load
step
7
t
7
t
o
OUT
o
5
to
5
r
r