A6280EA-T Allegro Microsystems Inc, A6280EA-T Datasheet - Page 7

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A6280EA-T

Manufacturer Part Number
A6280EA-T
Description
IC,Laser Diode/LED Driver,DIP,16PIN,PLASTIC
Manufacturer
Allegro Microsystems Inc
Type
PWM Controlr
Datasheet

Specifications of A6280EA-T

Constant Current
Yes
Topology
Linear, PWM
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
Through Hole
Package / Case
16-DIP (0.300", 7.62mm)
Operating Temperature
-40°C ~ 85°C
Current - Output / Channel
150mA
Internal Switch(s)
Yes
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Efficiency
-
Lead Free Status / RoHS Status
Lead free / RoHS Compliant, Lead free / RoHS Compliant
Other names
620-1256
A6280
PWM Brightness Control
The A6280 controls the intensity of each LED by pulse width
modulating the current of each output. The A6280 has three
10-bit brightness registers, one for each output. These brightness
registers set the PWM count value at which the outputs switch
off during each PWM cycle. Each 10-bit brightness register
gives 1023 levels of light intensity. The duty cycle, DC (%), can
be determined by the following equation:
where PWM
in the brightness register.
The relationship of the PWM
given in the following table:
When the brightness register is set to zero, the outputs remain off
for the duration of the PWM cycle for a 0% DC. When a bright-
ness register is set to 1023, the LED for that output remains on
(100% DC) when OEI is active and begins the PWM cycle. The
output remains on when the PWM counter rolls over and begins
a new count.
The PWM counter begins counting at zero and increments only
when the OEI pin is held low. When the PWM counter reaches
the count of 1024, the counter resets to zero and continues incre-
menting. The counter resets to zero on a rising edge of CI when
OEI is high, upon recovery from UVLO, and when powering-up.
Latching new data into the brightness registers will not reset the
PWM counter.
There is a programmable clock divider that can slow the PWM
counter relative to the CI pin. See table 1 for bit assignments of
the programmable clock divider. The PWM counter is incre-
Table 1. Clock Divider Configurations
n
7
0
1
0
1
DC = [(PWM
is the PWM value greater than zero that is stored
Bits
PWM
1023
. . .
8
0
0
1
1
0
1
2
n
n
+ 1) / 1024] ×100 (%),
n
value to the output duty cycle is
1024/1024 (100 %)
Divide By Count
÷ 1 (no division)
Duty Cycle
0/1024 (0 %)
2/1024
3/1024
. . .
÷ 2
÷ 4
÷ 8
3-Channel Constant-Current LED Driver
with
mented on every rising edge of the CI pin divided by the clock
divider count value when the OEI pin is low. For example, if
the clock divider is programmed to divide the CI by 2, then the
PWM counter will increment once every 2 CI cycles. Given a 5
MHz CI frequency, the clock period would be 200 ns.
The clock divider data in the shift register is latched on a rising
edge of the LI (Latch In) pin. The latched clock divider data
remains latched on a rising OEI signal.
The total number of possible colors of an RGB pixel is over
1 billion. Refer to figure 6 for the mapping of shift register bits
to latches.
Output Current Selection
The overall maximum current is set by the external resistor,
R
the maximum current remains constant regardless of the LED
voltage variation, supply voltage variation, temperature, or other
circuit parameters that could otherwise affect LED current. The
maximum output current can be calculated using the following
equation:
The relationship of the value selected for R
shown in figure 5.
Internal Linear Regulator
The A6280 has a built-in linear regulator. The regulator operates
from a supply voltage of 5.5 to 17 V. It allows the VIN pin of the
A6280 to connect to the same supply as the LEDs. This simpli-
fies board design by eliminating the need for a chip supply bus
EXT
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
Figure 5. Output Current versus External Resistor, R
0
, connected between the REXT and LGND pins. Once set,
5
Programmable
15
I
OUT
25
(max) = 753.12 / R
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
R
35
EXT
(kΩ)
45
PWM Control
EXT
EXT
55
.
and I
65
OUT
EXT
is
75
7

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