A8504EECTR-T Allegro Microsystems Inc, A8504EECTR-T Datasheet - Page 10

• Manufacturer Part Number: A8504EECTR-T
• Description: IC,Laser Diode/LED Driver,LLCC,28PIN,PLASTIC
• Manufacturer: Allegro Microsystems Inc
• Type: Backlight, White LED, RGBr

Specifications of A8504EECTR-T

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 8
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: RGB, White LED
• Frequency: 200kHz ~ 2MHz
• Voltage - Supply: 4.2 V ~ 5.5 V
• Voltage - Output: 47V
• Mounting Type: Surface Mount
• Package / Case: 26-WFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 45mA
• 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: 620-1215-2

A8504
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 A8504 identifies the open
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 be 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.
C4
C3
C1
C2
Startup
Symbol
C1
C2
C3
C4
Overvoltage condition
detected
t
The A8504 has protection against open
Parameter Units/Division
t
V
time
v
I
PWM
I
out
Figure 4. Timing of overvoltage protection (OVP) function when open
LEDs are detected at startup (left ) and during normal operation (right).
IN
out
WLED/RGB Backlight Driver for Medium Size LCDs
Normal operation
established
500 mA
200 mA
200 μs
5.00 V
5.00 V
V
V
PWM
I
OUT
OUT
V
V
PWM
I
OUT
OUT
I
IN
Figure 5. Overvoltage protection circuit. Three alternative
configurations at (A) are available, as follows:
C4
C3
C1
C2
OVP
Disable
LED opens
External Component
Normal
operation
both ROVP and DZ
ROVP only
DZ only
Symbol
Overvoltage condition
detected
C1
C2
C3
C4
t
V
IN
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
–
+
28.8 V
1.23 V
Parameter Units/Division
SW SW
t
V
time
v
PWM
I
I
out
IN
out
22 kΩ
4.4 kΩ
Normal operation restored
with open LED string
removed from control loop
D1
OVP
OVP Rating
redundancy
500 mA
100 mA
ROVP
200 μs
5.00 V
5.00 V
up to 45 V
up to 47 V
DZ
A
V
OUT
COUT
V
V
PWM
I
OUT
OUT
I
IN
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