A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 13

• 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
All unused pins should be connected with a 2.37 kΩ resistor to
ground, as shown in figure 5. The unused pin, with the pull-down
resistor, will be taken out of regulation at this point and will not
contribute to the boost regulation loop.
If a LEDx pin is shorted to ground the A8514 will not proceed
with soft start until the short is removed from the LEDx pin. This
prevents the A8514 from powering-up and putting an uncon-
trolled amount of current through the LEDs.
Soft start function
During soft start the LEDx pins are set to sink (I
boost switch current is reduced to the I
the inrush current generated by charging the output capacitors.
When the converter senses that there is enough voltage on the
LEDx pins the converter proceeds to increase the LED current to
the preset regulation current and the boost switch current limit is
switched to the I
necessary output power to the LEDs. This is shown in figure 6.
Frequency selection
The switching frequency on the boost regulator is set by the resis-
tor connected to the FSET/SYNC pin. The switching frequency
can be can be anywhere from 580 kHz to 2.3 MHz. Figure 7
shows the typical switching frequencies, in MHz, for given resis-
tor values, in kΩ.
In case during operation a fault occurs that will increase the
switching frequency, the FSET/SYNC pin is clamped to a
maximum switching frequency of no more than 3.5 MHz. If the
FSET/SYNC pin is shorted to GND the part will shut down. For
more details see the Fault Mode table later in this datasheet.
Figure 5. Channel select setup: (left) using only LED1, LED2, and LED3,
and (right) using all four channels.
GND
A8514
LED1
LED2
LED3
LED4
SW(LIM)
2.37 kΩ
level to allow the A8514 to deliver the
GND
A8514
LED1
LED2
LED3
LED4
SWSS(LIM)
LEDSS
level to limit
Wide Input Voltage Range, High Efficiency
) and the
Figure 7. Typical Switching Frequency versus value of R
Figure 6. Startup diagram showing the input current, output voltage, and
output current; shows I
(ch3, 20 V/div.), and PWM/EN (ch4, 5 V/div.), time = 1 ms/div.
C1
C2
C3
C4
I
V
PWM/EN
OUT
I
IN
2.1
1.9
1.7
1.5
1.3
1.1
0.9
0.7
0.5
OUT
Inrush current caused by
enabling the disconnect
switch (when used)
10.0
Fault Tolerant LED Driver
12.5
OUT
15.0
(ch1, 200 mA/div.), I
Resistance for R
17.5
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
t
20.0
22.5
SET
IN
Operation during
I
(kΩ)
SWSS(lim)
25.0
(ch2, 1 A/div.), V
Normal operation
I
SW(lim)
30.0
FSET
resistor.
32.5
OUT
35.0
13