A8515GLPTR-T Allegro Microsystems Inc, A8515GLPTR-T Datasheet - Page 16

• Manufacturer Part Number: A8515GLPTR-T
• Description: Backlight Driver For Medium Size LCDs
• Manufacturer: Allegro Microsystems Inc

Specifications of A8515GLPTR-T

• Constant Current: *
• Constant Voltage: *
• Internal Driver: *
• Type - Primary: *
• Type - Secondary: *
• Mounting Type: Surface Mount
• Topology: *
• Number Of Outputs: *
• Frequency: *
• Voltage - Supply: *
• Voltage - Output: *
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Operating Temperature: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A8515
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 13). As an
example: a system that delivers a full LED current of 120 mA per
LED would deliver 90 mA of current per LED when an APWM
signal is applied with a duty cycle of 25%. When this pin is not
used it should be tied to GND.
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
at least 5%. The LED ISET current is then trimmed down to the
Figure 13. Output current versus duty cycle; 200 kHz APWM signal.
Figure 15. Diagram showing the transition of LED current from 120 mA
to 90 mA, when a 25% duty cycle signal is applied to the APWM pin;
PWM = 1; shows I
PWM/EN (ch3, 5 V/div.), 500 μs/div.
C1
C2
C3
150
100
50
0
0
LED
20
(ch1, 50 mA/div.), APWM (ch2, 5 V/div.), and
PWM Duty Cycle, D (%)
40
PWM/EN
t
APWM
I
LED
60
80
Wide Input Voltage Range, High Efficiency
100
Figure 12. Simplified block diagram of the APWM ISET block.
Figure 16. Diagram showing the transition of LED current from 90 mA
to 120 mA, when a 25% duty cycle signal is removed from the APWM pin.
PWM = 1; shows I
PWM/EN (ch3, 5 V/div.), 500 μs/div.
C1
C2
C3
Figure 14. Percentage Error of the LED current versus PWM duty cycle;
200 kHz APWM signal.
–15
–10
–5
0
0
Fault Tolerant LED Driver
LED
(ch1, 50 mA/div.), APWM (ch2, 5 V/div.), and
20
APWM
ISET
PWM
PWM Duty Cycle, D (%)
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Current
Mirror
ISET
40
PWM/EN
t
APWM
I
LED
60
Current
Adjust
Driver
LED
A8515
80
100
16