A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 27

• 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
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:
A good approximation of efficiency, η , can be taken from the
efficiency curves located in the datasheet. A value of 90% is a
good starting approximation.
Step 4c
inductor 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. A first past
assumes I
then:
D(max)
I
I
IN
IN
(max) =
(min) =
Determining the duty cycle, calculated as follows:
Determining the inductor value. To ensure that the
Determining the maximum and minimum input current
I
ΔI
ripple
OUT
L =
L
=
= I
= 0.94 × 0.40 = 0.376 A
=
=
= #
=
=
0.376 (A)
=
to be 40% of the maximum inductor current:
ΔI
V
IN
1 –
35.36 (V)
1 –
4
35.36 (V)
V
L
IN
V
(max) × I
V
CHANNELS
OUT(OVP)
OUT(OVP)
V
(min)
IN
35.36 (V) + 0.4 (V)
10 (V)
IN
V
14 (V)
f
0.060 (A)
(min)
SW
OUT(OVP)
10 (V)
(max)
V
IN
2 (MHz)
ripple
10 (V)
(min)
240 (mA)
D(max)
240 (mA)
I
I
0.90
OUT
0.90
I
OUT
=
+
LED
0.240 A
V
d
=
0.72
=
0.94 A
=
72.04%
0.67 A
=
9.57 μH
Wide Input Voltage Range, High Efficiency
(12)
(13)
(14)
(15)
(16)
(17)
Step 4d
than I
A good inductor value to use would be 10 μH.
Step 4e
compensation for the inductor chosen. The slope compensation
value is determined by the following formula:
Next insert the inductor value used in the design:
Calculate the minimum required slope:
If the minimum required slope is greater than the calculated slope
compensation, the inductor value must be increased.
Note: The slope compensation value is in A/μs, and 1×10
constant multiplier.
Step 4f
current rating must be greater than the I
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.
Required Slope (min)
Slope Compensation =
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
This step is used to verify that there is sufficient slope
Double-check to make sure the ½ current ripple is less
Fault Tolerant LED Driver
L(min) = I
ΔI
L
Lused
, calculated as follows:
I
FSET
0.67 A > 0.19 A
=
=
= 0.94 (A) + 0.36 (A) / 2 = 1.12 A
IN
=
=
2.0 (MHz)
(min) >
f
IN
SW
1
ΔI
10 (μH)
0.36 (A)
V
values shown in figure 7. For example,
(max) +
1
Lused
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
3.6
IN
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
10 (V)
2 10
(min) D(max)
L
(1 – D(max))
used
1
/
2
f
1
SW
1
(1 – 0.72)
6
ΔI
2.0 (MHz)
/
1 10
2
10
L
f
ΔI
0.72
SW
=
–6
IN
Lused
3.6 A /μs
–6
(max) value plus the
= 2.57 A/μs
=
0.36 A
–6
is a
(18)
(19)
(20)
(21)
(22)
27