A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 26

• 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 Boost Configuration
This section provides a method for selecting component values
when designing an application using the A8514. The resulting
design is diagrammed in figure 34.
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
• 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
Step 2
Choose a 11.00 kΩ 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
A8514 is 700 mV. A constant term, 2 V, is added to give margin
to the design due to noise and output voltage ripple.
SW
A
BAT
f
(max): 65°C
at 60 mA: 3.2 V
: 2 MHz
: 10 to 14 V
Connect LEDs to pins LED1 and LED2.
Determining the LED current setting resistor R
Determining the OVP resistor. The OVP resistor is
The first step is determining the maximum voltage based
V
R
OUT(OVP)
ISET
= (1.003 (V) × 653) / 60 mA = 10.92 kΩ
= (V
= #
ISET
= 10 × 3.2 V+ 0.7 V + 2 V
= 34.7 V
SERIESLEDS
× A
LED
ISET
CHANNELS
: 60 mA
) / I
× V
LED
f
SERIESLEDS
: 4
+ V
LED
+ 2 (V)
Application Information
Wide Input Voltage Range, High Efficiency
: 10
LED
ISET
, of the
:
(7)
(8)
Then the OVP resistor is:
where both I
Characteristics table.
Chose a value of resistor that is higher value than the calculated
R
actual value of the minimum OVP trip level with the selected
resistor:
Step 3b
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
value V
of the boost converter must be reduced to meet the maximum
duty cycle requirements.
Step 4
that it can handle the necessary input current. In most applica-
tions, due to stringent EMI requirements, the system must operate
in continuous conduction mode throughout the whole input volt-
age range.
OVP
R
. In this case a value of 137 kΩ was selected. Below is the
V
D
OVP
V
OUT
Selecting the inductor. The inductor must be chosen such
OUT(OVP)
maxofboost
OUT(OVP)
d
At this point a quick check must be done to see if the
is the diode forward voltage.
(max)
= (V
= (34.7 (V) – 8.1 (V)) / 199 (μA) = 133.67 kΩ
OVPH
Fault Tolerant LED Driver
OUT(OVP)
. If this is not the case, the switching frequency
= 1 – 68 (ns) × 2.0 (MHz) = 86.4%
= 1 – t
= 137 (kΩ) × 199 (μA) + 8.1 (V) = 35.36 V
and V
=
=
1 – 0.864
10 (V)
1 – D
SWOFFTIME
OVP(th)
V
– V
IN
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
maxofboost
(min)
OVP(th)
OUT
OUT
SWOFFTIME
are taken from the Electrical
–
is then calculated as:
value must be greater than the
0.4 (V)
× f
) / I
SW
–
OVPH
V
=
) is found in the Electri-
d
73.13 V
(10)
(11)
(9)
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