A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 31

• Manufacturer Part Number: A8514KLPTR-T
• Description: IC LED DVR WHT 4X80MA 16-ETSSOP
• Manufacturer: Allegro Microsystems Inc

Specifications of A8514KLPTR-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A8514
tions, due to stringent EMI requirements, the system must operate
in continuous conduction mode throughout the whole input volt-
age range.
Step 4a
Step 4b
to the system. The minimum input current will dictate the induc-
tor value. The maximum current rating will dictate the current
rating of the inductor. First, the maximum input current, given:
then:
where η is efficiency.
Next, calculate minimum input current, as follows:
Step 4c
tor operates in continuous conduction mode, the value of the
inductor must be set such that the ½ inductor ripple current is not
greater than the average minimum input current. As a first pass
assume I
D(max)
I
I
IN
IN
(max) =
(min) =
Determining the duty cycle, calculated as follows:
Determining the inductor value. To ensure that the induc-
Determining the maximum and minimum input current
ripple
I
ΔI
OUT
L
= I
= 0.848 × 0.30 = 0.254 A
to be 30% of the maximum inductor current:
=
=
= #
=
=
=
IN
V
5 (V) + 15.9 (V) + 0.4 (V)
4
V
15.9 (V)
V
15.9 (V)
(max) × I
IN
V
CHANNELS
OUT(OVP)
OUT(OVP)
V
16 (V)
15.9 (V)
IN
(min)
IN
5 (V)
0.060 (A)
(min)
(max)
V
OUT(OVP)
+
ripple
V
+ 0.4 (V)
0.24 (A)
0.90
0.24 (A)
0.90
OUT(OVP)
I
I
OUT
I
OUT
LED
=
+
0.240 A
V
d
=
+
=
0.265 A
V
0.848 A
d
=
76.5%
Wide Input Voltage Range, High Efficiency
(35)
(36)
(37)
(38)
(39)
then:
Step 4d
than I
A good inductor value to use would be 10 μH.
Step 4e
mine the actual inductor ripple current:
Step 4f
current rating must be greater than the I
the ripple current ΔI
Step 5
frequency. Use the R
a 10 kΩ resistor will result in a 2 MHz switching frequency.
Step 6
must be chosen for three characteristics when it is used in LED
lighting circuitry. The most obvious two are: current rating of the
diode and reverse voltage rating.
IN
Determining the resistor value for a particular switching
Choosing the proper switching diode. The switching diode
(min):
Determining the inductor current rating. The inductor
Next insert the inductor value used in the design to deter-
Double-check to make sure the ½ current ripple is less
L =
=
Fault Tolerant LED Driver
L(min) = I
0.254 (A)
ΔI
ΔI
V
Lused
IN
L
(min)
L
I
FSET
0.265 A > 0.127 A
, calculated as follows:
= 0.848 (A) + 0.096 (A) = 0.944 A
IN
f
SW
=
=
5 (V)
(min) >
IN
10 (μH)
V
values shown in figure 7. For example,
(max) +
2 (MHz)
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
IN
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
5 (V)
D(max)
(min) D(max)
L
used
1
/
2
1
ΔI
2.0 (MHz)
/
2
L
f
ΔI
0.765
SW
0.765
IN
Lused
(max) value plus half of
=
7.53 μH
=
0.191 A
(40)
(41)
(42)
(43)
31