A8500EECTR-T Allegro Microsystems Inc, A8500EECTR-T Datasheet - Page 13

• 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
A typical application circuit for dimming an LCD monitor
backlight with 96 LEDs is shown in figure 1. Figure 12 shows
two dimming methods: digital PWM control (PWM signal on the
PWM pin) and analog PWM control, with the
applied to the ISET pin through a resistor, RA.
The current flowing through RA can be calculated as:
This current changes the reference current, I
LED current can be changed by changing V
changed in the range from 40 μA to 120 μA.
Application Circuit for 1000:1 Dimming Level
A wider dimming range can be achieved by changing the refer-
ence current, I
current levels turn on Q1. R
level. This current level can be set to 25 mA, and then it can be
dimmed by applying 100% to 0.32% duty cycle on the PWM pin.
The reference current can be reduced by turning off Q1. LED
current can be dimmed to 8 mA by reducing reference current
through ISET pin. This provides 1000:1 combined dimming level
range. Figure 14 shows the accuracy, Err
circuit.
SET
I
SET
, while using PWM dimming. For higher output,
= V
SET
C
C
Figure 12. Typical application circuit for PWM dimming, using digital PWM (on the
PWM pin, with APWM high).
/ R
I
A
ISET
SET
= V
RFSET
V
and R
A
A
– (V
RISET
/ R
RA
A
A
ISETP
.
– V
V
5 V ±10%
LEDX
IN
SET
A
set the 100% current
SET
. I
) / R
, results using this
analog signal, V
LED3 LED5 LED7 LGND
SET
PWM
APWM
SKIP
COMP
FSET
ISET
LED1
EN
, as follows:
A
Application Information
.
can be
VIN
A8500
A
,
SW SW
Flexible WLED/RGB Backlight Driver
LED8 LED6 LED4
Figure 13. Configuration for 1000:1 dimming.
Figure 14. Typical accuracy, normalized to the 100% current level,
versus dimming level, with F
ROVP
100
OVP
95
90
85
80
75
AGND
PGND
SEL3
SEL2
SEL1
LED2
0.1
COUT
V
IN
RISETP
Q1
for Medium Size LCDs
RISET
1.0
Dimming Level (%)
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
PWM
ISET
= 100 Hz.
10.0
100.0
13