A8510 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A8510' PDF : 33 Pages View PDF
A8510
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
APWM pin
The APWM pin is used in conjunction with the ISET pin. This is
a digital signal pin that internally adjusts the ISET current. The
typical input signal frequency is between 20 kHz and 1 MHz. The
duty cycle of this signal is inversely proportional to the percent-
age of current that is delivered to the LEDs (figure 14). As an
example, a system that delivers a full LED current of 40 mA per
LED would deliver 20 mA of current per LED when an APWM
signal is applied with a duty cycle of 50%. When this pin is not
used it should be tied to GND.
APWM
RISET
ISET
ISET
Current
Mirror
EN/PWM
A8510
APWM ISET
Current
Adjust
LED
Driver
Figure 13. Simplified block diagram of the APWM ISET block.
To use this pin for a trim function, the user should set the maxi-
mum output current to a value higher than the required current by
25
at least 5%. The LED ISET current is then trimmed down to the
20
5 V 200 kHz
40
15
1.5 V 200 kHz
30
1.5 V 50 kHz
10
20
5 V 50 kHz
10
5
0
0
20
40
60
80
100
PWM Duty Cycle, D (%)
0
0
20
40
60
80
100
PWM Duty Cycle, D (%)
Figure 14. LED current versus PWM duty cycle; 200 kHz APWM frequency. Figure 15. Percentage Error of the LED current versus APWM signals.
EN/PWM
C1
APWM
C2
EN/PWM
C1
APWM
C2
ILED
C3
t
Figure 16. Diagram showing the transition of LED current from 40 mA
to 20 mA, when a 50% duty cycle signal is applied to the APWM pin;
EN/PWM = 1; shows EN/PWM (ch1, 5 V/div.), APWM (ch2, 5 V/div.), and
ILED (ch3, 20 mA/div.), t = 1 ms/div.
ILED
C3
t
Figure 17. Diagram showing the transition of LED current from 20 mA
to 40 mA, when a 50% duty cycle signal is removed from the APWM pin.
EN/PWM = 1; shows EN/PWM (ch1, 5 V/div.), APWM (ch2, 5 V/div.), and
ILED (ch3, 20 mA/div.), t = 1 ms/div.
Allegro MicroSystems, Inc.
15
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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