A8500EECTR-T Allegro Microsystems Inc, A8500EECTR-T Datasheet - Page 12

• Manufacturer Part Number: A8500EECTR-T
• Description: IC,Laser Diode/LED Driver,LLCC,28PIN,PLASTIC
• Manufacturer: Allegro Microsystems Inc
• Type: Backlight, White LED, RGBr

Specifications of A8500EECTR-T

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 8
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: RGB, White LED
• Frequency: 2MHz
• Voltage - Supply: 4.2 V ~ 5.5 V
• Voltage - Output: 28V
• Mounting Type: Surface Mount
• Package / Case: 26-WFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 25mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Efficiency: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 620-1204-2

A8500
Calculate the value for R
where V
in Ω. For tighter OVP limits, a low–leakage-current Zener diode,
DZ, can be used, instead of ROVP, to set OVP at up to 47 V. For
redundancy, DZ can be connected across ROVP to provide addi-
tional protection, if ROVP should open. Select a 17 V low-leak-
age Zener diode for DZ.
Open LED Protection.
LEDs. If any enabled LED string opens, voltage on the corre-
sponding LEDx pin goes to zero. The boost loop operates in open
loop till the OVP level is reached. The A8500 identifies the open
OVP
is the desired typical OVP level in V, and R
R
OVP
= (V
The A8500 has protection against open
OVP
OVP
as follows:
– 30) / 54.9 μA ,
C2
C3
C1
Figure 11. Open LED fault protection.
I
V
I
OUT
IN
OUT
opens
LED string
Symbol
C1
C2
C3
OVP
t
is
Parameter Units/Division
Overvoltage
detected,
OVP begins
t
Flexible WLED/RGB Backlight Driver
V
time
I
OUT
I
OUT
IN
LED string when overvoltage on the OVP pin is detected. This
string is then removed from the boost controlling loop. The boost
circuit is then controlled in the normal manner, and the output
voltage is regulated, to provide the output required to drive the
remaining strings. If the open LED string is reconnected, it will
sink current up to the programmed current level.
Note: Open strings are removed from boost regulation, but not
disabled. This keeps the string in operation if LEDs open for only
a short length of time, or reach OVP level on a transient event.
The disconnected string can be restored to normal mode by re-
enabling the IC. It can also restored to normal operation if the
fault signal is removed from the corresponding LEDx pin, but an
OVP event occurs on any other LEDx pin.
500 mA
200 μs
50 mA
10 V
Normal operation
resumes with open
LED string removed
from control loop
for Medium Size LCDs
V
I
OUT
OUT
I
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
IN
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