A8515GLPTR-T Allegro Microsystems Inc, A8515GLPTR-T Datasheet - Page 18

• 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
Figure 19 illustrates when the output of the A8515 is discon-
nected from load during normal operation. The output voltage
instantly increases up to OVP voltage level and then the boost
stops switching to prevent damage to the IC. If the output is
drained off, eventually the boost might start switching for a short
duration until the OVP threshold is hit again.
Figure 20 displays a typical OVP event caused by an open LED
string. After the OVP condition is detected, the boost stops
switching, and the open LED string is removed from operation.
Afterwards V
resume switching and the A8515 will resume normal operation.
A8515 also has built-in secondary overvoltage protection to
protect the internal switch in the event of an open diode condi-
Figure 19. OVP protection in an output disconnect event; shows V
(ch1, 10 V/div.), SW node (ch2, 50 V/div.), PWM (ch3, 5 V/div.), and
I
Figure 21. OVP protection in an open Schottky diode event, while the IC is
in normal operation; shows PWM (ch1, 5 V/div.), SW node (ch2, 50 V/div.),
V
LED
C1
C1
OUT
C2
C3
C4
C2
C3
C4
(ch4, 200 mA/div.), 1 ms/div.
(ch3, 20 V/div.), and I
Output disconnect
event detected
condition detected
Open diode
OUT
is allowed to fall, and eventually the boost will
LED
(ch4, 200 mA/div.), 1 μs/div.
t
t
SW node
SW node
V
PWM
PWM
V
I
I
OUT
OUT
LED
LED
Wide Input Voltage Range, High Efficiency
OUT
tion. Open Schottky diode detection is implemented by detecting
overvoltage on the SW pin of the device. If voltage on the SW
pin exceeds the device safe operating voltage rating, the A8515
disables and remains latched. To clear this fault, the IC must be
shut down either by using the PWM signal or by going below
the UVLO threshold on the VIN pin. Figure 21 illustrates this.
As soon as the switch node voltage (SW) exceeds 60 V, the IC
shuts down. Due to small delays in the detection circuit, as well
as there being no load present, the switch node voltage will rise
above the trip point voltage.
Figure 22 illustrates when the A8515 is being enabled during an
open diode condition. The IC goes through all of its initial LED
detection and then tries to enable the boost, at which point the
open diode is detected.
Figure 20. OVP protection in an open LED string event; shows V
(ch1, 10 V/div.), SW node (ch2, 50 V/div.), PWM (ch3, 5 V/div.), and
I
Figure 22. OVP protection when the IC is enabled during an open diode
condition; shows PWM (ch1, 5 V/div.), SW node (ch2, 50 V/div.), V
(ch3, 10 V/div.), and I
LED
C2
C3
C1
C4
C1
C2
C3
C4
(ch4, 200 mA/div.), 500 μs/div.
Fault Tolerant LED Driver
LED
SW node
SW node
V
PWM
I
PWM
V
(ch4, 200 mA/div.), 500 μs/div.
OUT
LED
I
OUT
LED
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
t
t
condition detected
Open diode
condition detected
LED string open
OUT
OUT
18