A8513 データシートの表示（PDF） - Allegro MicroSystems

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A8513

Wide Input Voltage Range, High Efficiency Fault Tolerant LED Driver

Allegro MicroSystems 

A8513

Wide Input Voltage Range, High Efficiency

Fault Tolerant LED Driver

capacitors. After the A8513 senses there is enough voltage on the

LED pin, it increases the LED current to the preset regulation

current. The COMP pin will continue to source 80 uA until the

LEDs are able to run at the full preset current level.

Boost converter frequency

The switching frequency of the boost regulator is preset internally

to one of four frequencies. The frequency options are:

Part Number

A8513KLYTR-1-T

A8513KLYTR-2-T

A8513KLYTR-3-T

A8513KLYTR-4-T

Switching Frequency (fSW)

(MHz)

2

1

0.5

0.25

COMP

C1

VLED

C2

ILED

C3

C4

EN/PWM

LED current setting and LED dimming

The LED current, ILED , is set using the ISET pin, and can range

from 40 to 150 mA. Connect a resistor, RISET , between this pin

and GND to set the ILED current, according to the following

formula :

ILED

=

VISET

RISET

× AISET

(2)

=

1.003 V

RISET

× 1045

where ILED is in A and RISET is in Ω.

This formula sets the maximum current through the LEDs, which

is referred to as the 100% current.

PWM dimming

The LED current can be reduced from the 100% current level by

PWM dimming using the EN/PWM pin. When the EN/PWM pin

is pulled high, the A8513 turns on and the LED pin sinks 100%

current (figure 4). When EN/PWM is pulled low, the boost con-

verter and LED sink are turned off. The compensation (COMP)

pin is floated, and critical internal circuits are kept active.

The A8513 has very fast turn-on and turn-off times during PWM

dimming to minimize low PWM duty cycle errors. The typical

PWM signal delay tdPWM(on) is 250 ns (figure 5). The typical

tdPWM(off) time, between the PWM signal and the LED current

going low, is shown in figure 6.

t

Figure 4. Typical PWM dimming sequence, with PWM dimming frequency

of 1000 Hz and 10% duty cycle; shows COMP (ch1, 1 V/div.), VLED (ch2,

10 V/div.), ILED (ch3, 100 mA/div.), and EN/PWM (ch4, 5 V/div.),

time = 500 μs/div.

Analog dimming

The A8513 can also be dimmed by using an external DAC or

other voltage source applied either directly to the ground side of

the RISET resistor or through an external resistive divider to the

C3

ILED

C4

EN/PWM

t

Figure 5. Typical EN/PWM signal (5 V/div.) to LED current (100 mA/div.)

turn-on delay. The delay measured about 250 ns. VIN is 12 V, VOUT for 10

series LEDs is approximately 36 V, ILED is 150 mA. (time = 500 ns/div.)

C3

ILED

C4

EN/PWM

t

Figure 5. Typical EN/PWM signal (5 V/div.) to LED current (100 mA/div.)

turn-off delay. The typical delay is about 250 ns. (time = 500 ns/div.)

Allegro MicroSystems, Inc.

10

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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