A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 18

• 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
Although the APWM dimming function has a wide frequency
range, if this function is used strictly as an analog dimming
function it is recommended to use frequency ranges between
50 and 500 kHz for best accuracy. The frequency range must be
considered only if the user is not using this function as a closed
loop trim function. Another limitation is that the propagation
delay between this APWM signal and I
seconds to change the actual LED current. This effect is shown in
figures 16, 17, and 19.
Analog dimming
The A8514 can also be dimmed by using an external DAC or
another voltage source applied either directly to the ground side
of the R
pin (see figure 19). The limit of this type of dimming depends on
the range of the ISET pin. In the case of the A8514 the limit is
20 to 125 μA.
• For a single resistor (panel A of figure 20), the ISET current is
controlled by the following formula:
where V
voltage.
When the DAC voltage is 0 V the LED current will be at its
Figure 20. Simplified diagrams of voltage control of I
applications using a DAC to control I
and dual resistors (lower).
ISET
ISET
resistor or through an external resistor to the ISET
is the ISET pin voltage and V
DAC
DAC
GND
GND
I
SET
VDAC
VDAC
=
V
ISET
R
R1
R
ISET
R
ISET
– V
(A)
(B)
ISET
LED
DAC
using a single resistor (upper),
OUT
ISET
ISET
DAC
takes several milli-
A8514
A8514
GND
GND
LED
is the DAC output
: typical
Wide Input Voltage Range, High Efficiency
(3)
Figure 21. Example of the disabling of an LED string when the LED pin
voltage is increased above 4.6 V; shows I
(ch2, 5 V/div.), and PWM/EN (ch3, 5 V/div.), time = 10 μs/div.
maximum. To keep the internal gain amplifier stable, the user
should not decrease the current through the R
than 20 μA
• For a dual-resistor configuration (panel B of figure 20), the I
current is controlled by the following formula:
The advantage of this circuit is that the DAC voltage can be
higher or lower, thus adjusting the LED current to a higher or
lower value of the preset LED current set by the R
LED short detect
Both LEDx pins are capable of handling the maximum V
that the converter can deliver, thus providing protection from the
LEDx pin to V
An LEDx pin that has a voltage exceeding V
removed from operation (see figure 21). This is to prevent the IC
from dissipating too much power by having a large voltage pres-
ent on an LEDx pin.
C1
C2
C3
▫ V
▫ V
▫ V
DAC
DAC
DAC
= 1.003 V; the output is strictly controlled by R
> 1.003 V; the LED current is reduced
< 1.003 V; the LED current is increased
I
Fault Tolerant LED Driver
SET
OUT
=
in the event of a connector short.
V
R
ISET
ISET
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
–
PWM/EN
LED1
V
I
OUT
t
DAC
R
– V
OUT
1
ISET
(ch1, 200 mA/div.), LED1
LEDSC
ISET
resistor to less
ISET
will be
resistor:
ISET
OUT
SET
(4)
18