A6281EESTR-T Allegro Microsystems Inc, A6281EESTR-T Datasheet - Page 8

• Manufacturer Part Number: A6281EESTR-T
• Description: IC LED DRIVER PWM CONTROL 16-QFN
• Manufacturer: Allegro Microsystems Inc
• Type: PWM Controlr

Specifications of A6281EESTR-T

• Topology: Linear, PWM
• Constant Current: Yes
• Number Of Outputs: 3
• Internal Driver: Yes
• Type - Secondary: RGB
• Frequency: 5MHz
• Voltage - Supply: 4.75 V ~ 17 V
• Voltage - Output: 1 V ~ 3 V
• Mounting Type: Surface Mount
• Package / Case: 16-WFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 150mA
• Internal Switch(s): Yes
• Led Driver Application: Architectural Lighting, Displays
• No. Of Outputs: 3
• Output Current: 165mA
• Output Voltage: 3V
• Input Voltage: 4.75V To 17V
• Operating Supply Voltage (typ): 5/9/12/15V
• Number Of Segments: 3
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: QFN EP
• Pin Count: 16
• Mounting: Surface Mount
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (max): 17V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Efficiency: -
• Lead Free Status / Rohs Status: Compliant
• Other names: 620-1218-2

A6281
intended as an external power source. There should be a 1.0 μF,
10 V ceramic capacitor connected between the V REG pin and
LGND. The capacitor should be located as close to the V REG
pin as possible.
Dot Correction Control
The A6281 can further control the maximum output current for
each output by setting the three 7-bit dot correction registers
with scale data that ranges from 36.5% to 100% of the overall
maximum output current that is set by the REXT resistor. This
feature is useful because not every type of LED (red, green, or
blue, for example) has the same level of brightness for a given
current, and the brightness could be different even from LED to
LED of the same type. By scaling the output currents so that all
the LEDs have matched intensities, the application will have full
color depth when using the PWM counters. The dot correction
current can be calculated by the following equation:
Where Scale
table:
Refer to figure 5 for the bit configurations for the scalar registers.
The dot correction data in the shift register is latched on a rising
edge of the LI pin. The dot correction data remains latched on a
rising OEI signal. The default output current when the A6281
is powered-up or recovers from a UVLO is 36.5% of the current
set by the R
Package Power Dissipation
The maximum allowable package power dissipation is deter-
mined as:
I
OUTn
EXT
n
is in the range 0 to 127, as shown in the following
= I
resistor.
P
D
Scale
OUTn
127
(max) = (150 – T
. . .
0
1
2
(max) × (Scale
I
OUT
A
/I
36.5
37.0
37.5
OUT
100
) / R
(%)
. . .
n
/ 2 + 36.5) / 100
(max)
θJA
.
3-Channel Constant Current LED Driver
with Programmable PWM Control
The actual package power dissipation is:
where DC
output current for channel i, determined by the dot correction
current for that channel and REXT.
When calculating power dissipation, the total number of avail-
able device outputs is usually used for the worst-case situation
(3 LEDs at 100% duty cycle).
Thermal Shutdown (TSD)
When the junction temperature of the A6281 reaches the thermal
shutdown temperature threshold, T
outputs will shut off until the junction temperature cools down
below the recovery threshold, T
shift register and output latches will remain active during the
TSD event. Therefore there is no need to reload the data into the
output latches.
Undervoltage Lockout
The A6281 includes an internal undervoltage lockout (UVLO)
circuit that disables the driver outputs in the event of the logic
supply voltage dropping below a minimum acceptable level.
This prevents the display of erroneous information, a necessary
function for some critical applications. The shift register will not
shift any data in a UVLO condition. Upon recovery of the logic
supply voltage and on power up, the internal shift register and all
latches will be set to zero.
Ballast Resistors
The voltage on the outputs should be kept in the range 1 to 3 V.
If the voltage goes below 1V, the current will begin to rolloff as
the driver runs out of headroom. At V
dissipation may become a problem, as each output contributes
V
power supply nominal voltage is chosen to keep the output volt-
age in this range. Alternatively, series resistors can be added to
dissipate the extra power and keep the output voltage within the
recommended range.
OUT
× I
LED
i
is the PWM duty cycle for channel i, and I
of power loss in the output sink driver. Typically the
P
D(act)
= DC
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
+ DC
+ DC
0
JTSD
× V
1
2
× V
× V
JTSD
DS0
–∆T
DS1
DS2
OUT
× I
(165°C typical), the
× I
× I
J
OUT0
above 3 V, the power
( 15°C typical). The
OUT1
OUT2
+ V
IN
OUTi
× I
IN
is the
,
8