A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 30

• 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
Design Example for SEPIC Configuration
This section provides a method for selecting component values
when designing an application using the A8514 in SEPIC (Sin-
gle-Ended Primary-Inductor Converter) circuit. SEPIC topology
has the advantage that it can generate a positive output voltage
either higher or lower than the input voltage. The resulting design
is diagrammed in figure 35.
Assumptions: For the purposes of this example, the following are
given as the application requirements:
• V
• Quantity of LED channels, #
• Quantity of series LEDs per channel, #
• LED current per channel, I
• LED V
• f
• T
• PWM dimming frequency: 200 Hz, 1% duty cycle
Procedure: The procedure consists of selecting the appropriate
configuration and then the individual component values, in an
ordered sequence.
Step 1
channels are needed, the unused LEDx pins should be pulled to
ground using a 1.5 kΩ resistor.
Step 2
Choose an 11.00 kΩ 1% resistor.
Step 3
connected between the OVP pin and the output voltage of the
converter.
Step 3a
on the LED requirements. The regulation voltage, V
SW
A
BAT
(max): 65°C
: 2 MHz
: 6 to 14 V ( V
Connecting LEDs to LEDx pins. If only some of the LED
Determining the LED current setting resistor R
Determining the OVP resistor. The OVP resistor is
The first step is determining the maximum voltage based
f
at 60 mA: ≈ 3.3 V
R
ISET
= (V
= (1.003 (V) × 653) / 0.60 (A) = 10.92 kΩ
IN
ISET
(min): 5 V and V
× A
LED
ISET
CHANNELS
: 60 mA
) / I
LED
IN
SERIESLEDS
: 4
(max): 16 V )
Wide Input Voltage Range, High Efficiency
: 4
LED
ISET
, of the
:
(30)
A8514 is 700 mV. A constant term, 2 V, is added to give margin
to the design due to noise and output voltage ripple.
Then the OVP resistor is:
where both I
Characteristics table.
In this case a value of 39.2 kΩ was selected. Below is the actual
value of the minimum OVP trip level with the selected resistor:
Step 3b
the conversion ratio is acceptable for the selected frequency.
where the minimum off-time (t
cal Characteristics table.
The Theoretical Maximum V
where V
The Theoretical Maximum V
the value V
to reduce the frequency to allow the boost to convert the volt-
age ratios.
Step 4
that it can handle the necessary input current. In most applica-
V
V
R
OUT
OUT(OVP)
OVP
V
Selecting the inductor. The inductor must be chosen such
(max) =
OUT(OVP)
d
At this point a quick check must be done to determine if
= (V
= (15.9 (V) – 8.1 (V)) / 0.199 (mA) = 39.196 kΩ
is the diode forward voltage.
OUT(OVP)
D
OVPH
Fault Tolerant LED Driver
max
= #
= 4 × 3.3 (V) + 0.7 (V) + 2 (V) = 15.9 V
OUT(OVP)
=
= 1 – 68 (ns) × 2 (MHz) = 86.4%
= 1 – t
= 39.2 (kΩ) × 0.199 (mA) + 8.1 (V) = 15.9 V
SERIESLEDS
V
and V
5 (V)
IN
. If this is not the case, it may be necessary
(min)
SWOFFTIME
– V
OVP(th)
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
OVP(th)
1 – 0.86
OUT
OUT
× V
0.86
1 – D
SWOFFTIME
are taken from the Electrical
D
f
is then calculated as:
value must be greater than
+ V
max
) / I
× f
max
–
LED
OVPH
SW
0.4 (V)
–
) is found in the Electri-
+ 2 (V)
V
d
=
30.3 V
(31)
(32)
(33)
(34)
30