Description
The A6280 is a 3-channel constant current LED driver that
has a wide range of output currents. The A6280 controls LED
brightness with a Pulse Width Modulation (PWM) scheme
that gives the application the capability of displaying a billion
colors in an RGB cluster. The maximum current is set by an
external resistor.
The LED brightness is controlled by performing PWM control
on the outputs. The brightness data of the PWM signal for
each LED is stored in three 10-bit registers. The peak value
for each LED can be adjusted (dot-corrected) to compensate
for mismatch, aging, and temperature effects. All the internal
latched registers are loaded by a 31-bit shift register. One
address bit controls whether dot correction/clock divider ratio
or brightness data is loaded into the registers. The remaining
bits are used for the data. This helps reduce the pin count of
the A6280. To further lower the A6280 pin count, the PWM
clock and the serial bus clock share the same pin and work
concurrently to control LED brightness and to load data.
The A6280 is designed to minimize the number of components
needed to drive LEDs with large pixel spacing. A large number
of A6280s can be daisy chained together and controlled by
just four control signals (clock, serial data, latch, and output
enable). Each of these inputs has buffered outputs to drive
the next chip in the chain. Also, VIN can be tied to the LED
A6280-DS, Rev. 5
3-Channel Constant-Current LED Driver
with Programmable PWM Control
Continued on the next page…
Packages: 16 pin DIP (suffix A), and
16 pin QFN (suffix ES)
Application Diagram
ES, approximate scale 1:1
A6280
Clock
Data
Output Enable
Latch Enable
Microprocessor
Control Board
Clock Out
Data Out
Latch Out
OE Out
Clock In
Data In
Latch In
OE In
VLED
OutB
OutG
OutR
VIN
Power Supply Bus
A6280
Pixel Board #1
REXT
VREG
Clock Out
Data Out
OE Out
Clock In
Data In
OE In
VLED
OutB
OutG
OutR
VIN
A6280
Pixel Board #2
REXT
VREG
Pixel Board #N
Latch OutLatch In
Cat5 UTP Cat5 UTP Cat5 UTP
Figure 1. Functional drawing of daisy chained display application. Additional pixel boards
with A6280 ICs can be applied.
Features and Benefits
▪ 3 × 10-bit PWM brightness settings
▪ 3 × 7-bit dot correction current settings
▪ 5 to 17 V operation
▪ Wide output current range, 10 to 150 mA per channel
▪ Serial port/PWM clock operates at up to 5 MHz
▪ Data and clock logic architecture allows single
microcontroller control of large quantities of serially-
connected A6280s at fast data transfer rate
▪ Buffered logic outputs to drive cables
▪ Thermal shutdown and UVLO protection
▪ Power-On Reset
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Part Number Packing* Mounting
A6280EA-T 25 pieces/tube 16 pin DIP
A6280EESTR-T 1500 pieces/reel 16 pin QFN
*Contact Allegro for additional packing options.
Selection Guide
voltage supply bus, thus eliminating the need for a separate chip
supply bus or an external regulator.
Applications include:
▪ Colored, large-character LED signs
▪ Scrolling, colored marquees
▪ Architectural lighting
▪ High intensity monochrome displays
▪ Large video and graphic displays
The A6280 is supplied in a 16-pin dual in-line (DIP) package
(suffix ‘A’) and in a 16-lead QFN (suffix ‘ES’) package. The
packages are lead (Pb) free with 100% matte-tin leadframe
plating.
Description (continued)
Thermal Characteristics
Characteristic Symbol Test Conditions* Rating Units
Package Thermal Resistance RθJA
Package A, 4 layer PCB 38 ºC/W
4-layer PCB based on JEDEC standard (estimated performance) 42 ºC/W
*For additional information, refer to the Allegro website.
25 50 75 100 125 150
Temperature (°C)
Power Dissipation, P
D
(mW)
3500
3250
3000
2750
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
Power Dissipation versus Ambient Temperature
(R
QJA
= 38 ºC/W)
Package A, 4 layer PCB
(R
QJA
= 42 ºC/W)
4 layer PCB (estimated)
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Units
Load Supply Voltage VIN 17 V
Output Voltage VOUT OUT0, OUT1, OUT2 –0.5 to 17 V
Output Current IOUT 170 mA
Ground Current IGND 600 mA
VREG Pin VREG 6V
Logic Outputs VOCO, LO, OEO, SDO 7 V
Logic Input Voltage Range VICI, LI, OEI, SDI –0.3 to 7 V
Operating Ambient Temperature TARange E –40 to 85 ºC
Maximum Junction Temperature TJ(max) 150 ºC
Storage Temperature Tstg –55 to 150 ºC
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OUT2OUT1OUT0
Regulator
Current
Regulator 0
Current
Regulator 1
Current
Regulator 2
Latched Registers
REXT
R
EXT
LGNDPGND
OEO
OEI
VIN
VREG
LI LO
Shift Register
SDI
CI
SDO
CO
100 ns
One-Shot
Terminal List Table
Name Number Description
A Package ES Package
OUT1 1 11 Sinking output terminal
OUT0 2 12 Sinking output terminal
SDO 3 13 Buffered serial data output after shift register
LO 4 14 Buffered latch output
OEO 5 15 Buffered output enable output
CO 6 16 Buffered clock output
REXT 7 1 An external resistor at this terminal establishes overall output current
VREG 8 2 Regulator decoupling
LGND 9 3 Logic ground
VIN 10 4 Chip power supply voltage
CI 11 5 Serial and PWM clock input
OEI 12 6 Output enable input; when low (active), the output drivers are enabled; when high (inac-
tive), all output drivers are turned off (blanked)
LI 13 7 Latch input terminal; serial data is latched with high-level input
SDI 14 8 Serial data input to shift register
OUT2 15 9 Sinking output terminal
PGND 16 10 Power ground
PAD n.a. – Exposed thermal pad, not internally connected; connect externally to LGND and PGND.
Pin-out Drawings
Package A
Package ES
Functional Block Diagram
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PGND
OUT2
SDI
LI
OEI
CI
VIN
LGND
OUT1
OUT0
SDO
LO
OEO
CO
REXT
VREG
12
11
10
9
1
2
3
4
5
6
7
8
16
15
14
13
CO
OEO
LO
SDO
CI
OEI
LI
SDI
OUT0
OUT1
PGND
OUT2
REXT
VREG
LGND
VIN
PAD
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OPERATING CHARACTERISTICS, valid at TA = 25°C, VIN = 4.75 to 17.0 V, unless otherwise noted
Characteristic Symbol Test Conditions Min. Typ. Max. Units
ELECTRICAL CHARACTERISTICS
Quiescent Supply Current IDD fCLKIN = 0.0 Hz – – 5.0 mA
Operating Supply Current IDD fCLKIN = 5 Mhz – – 15.0 mA
Load Supply Voltage VIN 4.75 – 17 V
Undervoltage Lockout VIN(UV)
VIN rising 3.5 – 4.5 V
VIN falling 3.0 – 4.0 V
VREG Voltage Range1VREG IO =15 mA, VIN = 17 V 4.6 – 5.4 V
Output Current (any single output) IOUT
REXT = 5 k, scalar = 100% 135 150.0 165 mA
REXT = 15 k, scalar = 100% 45 51 57 mA
Output to Output Matching Error2Err Output to output variation—all outputs on, REXT = 5 k–7 – 7 %
Output Voltage Range VDS(min) 1.0 – 3.0 V
Load Regulation (I%Diff / VDS)R
EXT = 5 k, VDS = 1 to 3 V – ±1 ±3 %/V
Output Leakage Current IDSX VOH = 17 V – – 1.0 A
Logic Input Voltage VIH 2.0 – – V
VIL – – 0.8 V
Logic Input Voltage Hysteresis All digital inputs – 150 – mV
Logic Output Voltage VOL VIN 5.0 V, IO = ±2 mA – – 0.4 V
VOH 3.8 – – V
Input Resistance RI
OEI pin, pull-up 150 300 600 k
LI pin, pull-down 100 200 400 k
CI and SDI Pins Logic Input Current IIN VIN = 0 to 5 V –20 – 20 A
Output Dot Correction Error REXT = 5 k; LSB – ±1 – bit
Thermal Shutdown Temperature TJTSD Temperature increasing – 165 – °C
Thermal Shutdown Hysteresis TJhys –15–°C
SWITCHING CHARACTERISTICS
Clock Hold Time tH(CLK) 20 – – ns
Data Setup Time tSU(D) 20 – – ns
Data Hold Time tH(D) 20 – – ns
Latch Setup Time3tSU(LI) 20 – – ns
Latch Hold Time tH(LI) 20 – – ns
Output Enable Set Up Time tSU(OE) 40 – – ns
Output Enable Falling to Outputs Turning ON
Propagation Delay Time tP(OE)2 – 200 – ns
Clock to Output Propagation Delay Time tP(OUT) VDS = 1.0 V, IOUT = 150 mA – 200 – ns
Logic Output Fall Time tBF COB = 50 pF, 4.5 to 0.5 V – 50 100 ns
Logic Output Rise Time tBR COB = 50 pF, 0.5 to 4.5 V – 30 60 ns
Output Fall Time (Turn Off) tf
CO = 10 pF, 90% to 10% of IOUT = 10 mA – 10 – ns
CO = 10 pF, 90% to 10% of IOUT = 150 mA – 10 – ns
Output Rise Time (Turn On) tr
CO = 10 pF, 10% to 90% of IOUT = 10 mA – 50 – ns
CO = 10 pF, 10% to 90% of IOUT = 150 mA – 100 – ns
Clock Falling Edge to Serial Data Out
Propagation Delay Time tP(SDO) – 50 100 ns
Output Enable In to Output Enable Out
Propagation Delay tP(OE) – 50 100 ns
Latch In to Latch Out Propagation Delay tP(LE) – 50 100 ns
Clock In to Clock Out Propagation Delay tP(CLK) – 50 100 ns
Clock Out Pulse Duration tw(CLK) 70 100 130 ns
Maximum CLKIN Frequency fCLKIN – – 6 MHz
1If VIN is a 4.75 to 5.5 V supply, connect VIN to VREG externally
2Err = [IO UT(min or max) – IOUT(av)] / IOUT(av), where IOUT(av) is the average of 3 output current values.
3In daisy-chained applications, tSU(LI) must be increased for the quantity of pixels in the chain (see Application Information section).
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
15 16 31
CI
(Clock In)
SDI
(Serial Data In)
SDO
(Serial Data Out)
LI
(Latch In)
LO
(Latch Out)
D30 D28 D27 D26 D24 D23 D22 D21 D15 D14 D0
D30Don’t Care
t
w(CLK)
t
SU(D )
t
H( D)
t
P(SD O )
t
SU(LI )
t
H(LI)
t
P(IO)
D29
012345678
CI
(Clock In)
t
SU(O E )
PWM Counter
OEI
(Output Enable Input)
OEO
(
Output Enable Output)
I
OUT0
I
OUT1
I
OUT2
Brightness Data= 0
Brightness Data= 1
Brightness Data = 1022
t
P(O E )
t
w(OE)
tP(OE)2 tP(OUT)
tP(OUT)
tP(OUT)
0 1 2 1023 0 0X
T
1
T
0
T
2
T
N
1 2
Outputs Off
Outputs On
Figure 2. Shift Register Timing
Figure 3. PWM Counter and Output Timing
Timing Diagrams
NOTE: At least one rising edge on the CI pin is needed while OE is high in order to reset the PWM counter and start
a new PWM cycle. Otherwise, when OE is brought low, the outputs will operate according to the current PWM data
and PWM count, and will finish the current cycle before resetting the count to 0. Therefore, if the counter is not reset
(as explained above) after new PWM data has been latched, the outputs will complete the current PWM cycle (up to
1024 clock pulses if no clock divider is selected, 2048 clock pulses if a divide-by count of 2 is selected, and so forth)
before starting a new PWM cycle with the new data.
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OUT2OUT1OUT0
Current
Regulator 0
Current
Regulator 1
Current
Regulator 2
100 ns
One-Shot
+5 V
Regulator
Shift Register
Latched Registers
SDI
REXT
R
EXT
LGNDPGND
CI
SDO
CO
OEO
OEI
VIN
VREG
LI LO
0 to 6 97 to 8 10 to 16 17 to 19 20 to 26 28 to 2927 30
Current
Scalar 0
7 Bits
Clock
Divider
2 Bits
Unused
1 Bit
Current
Scalar 2
7 Bits
Unused
1 Bit
Test
Bits
2 Bits
Bit 30
“1”
Current
Scalar 1
7 Bits
Unused
3 Bits
PWM Counter 0
10 Bits
PWM Counter 1
10 Bits
PWM Counter 2
10 Bits Bit 30
“0”
Figure 4. Functional Diagram
Functional Description
Shift Register
The A6280 has a 31 bit shift register that loads data through the
SDI (Serial Data In) pin. The shift register operates by a first-in
first-out (FIFO) method. The most significant bit (MSB, bit 30)
is the first bit shifted in and the least significant bit (LSB, bit 0)
is shifted in last. The serial data is clocked by a rising edge of
the CI (Clock In) pin. The SDO (Serial Data Out) pin is updated
to the state of bit 30 on the falling edge of the CI pin. This will
prevent any race conditions and erroneous data that might occur
while propagating information through multiple A6280 that are
daisy chained together. The contents of the shift register will
continue to propagate on every rising edge of the CI pin. The
information in the shift register is latched on a rising edge of the
LI (Latch In) pin. The LI pin must be brought low before the ris-
ing edge of the next clock pulse, to avoid latching erroneous data.
The latched data remains latched on a rising OEI (Output Enable
In) signal.
Output Buffers
The A6280 is designed to allow daisy chaining many A6280s
together. It can pass the clock, data, latch, and output enable
signals from one A6820 to the next without any loss of data due
to duty cycle skewing or signal degradation.
The A6820 is equipped with output buffers that allow the data
signals to travel over long distances through strings of A6280s
without the need for extra driving hardware. The A6280 drives
these signals to TTL levels. Each of the A6280 inputs have a cor-
responding buffered output:
• CI (Clock In) pin to CO (Clock Out) pin
• LI (Latch In) pin to LO (Latch Out) pin
• OEI (Output Enable In) pin to OEO (Output Enable Out) pin
• SDI (Serial Data In) pin to SDO (Serial Data Out) pin
The CO (Clock Out) pin is driven by an internal one-shot circuit.
When the CI pin detects an edge rising through the input thresh-
old, the one-shot circuitry drives the CO pin high for 100 ns. The
CI pin input threshold has hysteresis to prevent false triggering
of the CO signal. The implementation on the one-shot solution
allows many A6280s to be daisy chained together with a consis-
tent clock signal throughout the entire chain without degradation
or loss of synchronicity to the data line.
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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:
DC = [(PWMn
+ 1) / 1024] ×100 (%),
where PWMn is the PWM value greater than zero that is stored
in the brightness register.
The relationship of the PWMn value to the output duty cycle is
given in the following table:
PWMnDuty Cycle
0 0/1024 (0 %)
1 2/1024
2 3/1024
. . . . . .
1023 1024/1024 (100 %)
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-
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,
REXT , connected between the REXT and LGND pins. Once set,
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:
IOUT(max) = 753.12 / REXT.
The relationship of the value selected for REXT and IOUT is
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
Table 1. Clock Divider Configurations
Bits Divide By Count
78
00 ÷ 1 (no division)
10 ÷ 2
01 ÷ 4
11 ÷ 80
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
515253545556575
REXT (kΩ)
I
OUT
(mA)
Figure 5. Output Current versus External Resistor, REXT
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
and external voltage regulators. For 5 V supplies, connect VIN
to VREG externally. Note: When using 5 V supplies, ensure that
VIN does not exceed the absolute maximum rating of the VREG
pin (6 V).
The V
REG pin is used by the internal linear regulator to connect
to a bypass capacitor. This pin is for internal use only and is not
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 A6280 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:
IOUTn = IOUTn(max) × (Scalen / 2 + 36.5) / 100
Where Scalen is in the range 0 to 127, as shown in the following
table:
Scale IOUT/IOUT(max)
(%)
0 36.5
1 37.0
2 37.5
. . . . . .
127 100
Refer to figure 6 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 (Latch In) pin. The dot correction data remains
latched on a rising OEI signal. The default output current when
the A6280 is powered-up or recovers from a UVLO is 36.5% of
the current set by the REXT resistor.
Package Power Dissipation
The maximum allowable package power dissipation is deter-
mined as:
PD(max) = (150 – TA) / RθJA .
The actual package power dissipation is:
PD(act) = DC0 × VDS0 × IOUT0
+ DC1 × VDS1 × IOUT1
+ DC2 × VDS2 × IOUT2 + VIN × IIN .
where DCi is the PWM duty cycle for channel i, and IOUTi is the
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
(i.e., displaying all 3 LEDs at 100% DC).
Thermal Shutdown (TSD)
When the junction temperature of the A6280 reaches the thermal
shutdown temperature threshold, TJTSD (165°C typical), the
outputs will shut off until the junction temperature cools down
below the recovery threshold, TJTSD –∆TJ ( 15°C typical). The
shift register and output latches will remain active during the
TSD event. Therefore there is no need to reset the data in the
output latches.
Figure 6. Register Configuration
Bits
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30a
PWM Counter 0 PWM Counter 1 PWM Counter 2 Address “0”
Dot Correction
Register 0
Clock
Mode 0Dot Correction
Register 1 000 Dot Correction
Register 2 0ATB
bATBbAddress “1”
aSelects which word is written to: Dot Correction/Clock Mode selection or PWM counter.
bAllegro Test Bit (ATB). Reserved for Allegro internal testing. Always set to zero (0) in the application.
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Undervoltage Lockout
The A6280 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 func-
tion 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 VOUT above 3 V, the power
dissipation may become a problem, as each output contributes
VOUT × ILED of power loss in the output sink driver. Typically the
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.
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Timing Considerations
A6280s can be used in large numbers to drive many LEDs with
the control signals connected serially together, with short cables
between each pixel (see figure 8). Because the clock negative
edge drives the data to the SDO (Serial Data Out) pin, and the
CO pin is driven by a 100 ns one-shot function, the clock and
data signals remain synchronized with each other as you move
from the first pixel in the chain to the last.
After all of the data is written to each A6280 in the chain, the
data is latched into each A6280 via a low-to-high transition on
the LI pin. The LO pin of pixel #1 drives the LI pin of pixel #2,
and so on down the chain. These signals are buffered and are
driven asynchronously relative to the CI and SDI pins. Therefore
the mismatch in delays between CO and LO must be taken into
consideration.
Although the mismatches in delays are quite small, they must be
considered when creating the timing pattern for driving the chain.
The key parameter is the setup time from the last CI clock rising
edge to the rising edge of LI.
The minimum A6280 setup time from CI to LI is 20 ns. There
may be a 5 ns per pixel mismatch in the propagation delays of the
CI and LI signals (the delay from CI to CO compared to the delay
from LI to LO). As a rule of thumb, use a setup time, tsu , at the
first A6280 in the chain as calculated below:
tsu = 20 ns + n × 5 ns ,
where n is the number of pixels in the chain.
This will ensure that the setup time at the last pixel in the chain is
at least 20 ns.
Application Information
Figure 7. Signal Delay Mismatch Timing Diagram. tsu is the setup time for signals (CI to
LI) applied to the first pixel in the chain. Note the difference in delay for CI(1) to CI(n)
compared to the delay for LI(1) to LI(n). This must be compensated by increasing tsu.
CO(1) = CI (2)
CI(1)
CO(2) = CI (3)
CO(n-1) = CI(n)
LI (1)
LO (1) = LI (2)
LO (2) = LI (3)
LO (n-1) = LI (n)
CI(1) to CI(n)
tsu
LI(1) to LI(n)
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Clock
Data
Output Enable
System Logic
CO
OEO
LO
SDO
A6280
A6280
Maximum of
250 pixels
Latch
Clock
Data
Output Enable
System Logic
CO
OEO
LO
SDO
A6280
A6280
Maximum of
250 pixels
Latch
Tie LGND and PGND
to PAD externally
8.5 V
10 kΩ
1 μF
X5R
10 μFVOn
1 to 3 V
CI
OEI
LI PAD
SDI
Red
LEDs
Green
LEDs
Blue
LEDs
OUT2
PGND
OUT1
OUT0
REXT
VREG
LGND
VIN
Tie LGND and PGND
to PAD externally
VOn
1 to 3 V
CI
OEI
LI PAD
SDI
OUT2
PGND
OUT1
OUT0
REXT
VREG
LGND
VIN
–
+
–
+
10 V
5 kΩ
1 μF
10 V
10 μF
2 Ω
0.5 W
Applications Drawings
Figure 8. Application Driving 3 RGB LEDs at 75 mA Peak
Figure 9. Application Driving High Power LED at 450 mA
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
A Package, 16 Pin DIP
2
0.750
0.250 0.430
0.210
0.300
0.010
0.018
0.100
0.130
0.060
0.005
1
16
A
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
ATerminal #1 mark area
All dimensions nominal, not for tooling use
(reference JEDEC MS-001 BB)
Dimensions in inches
ES Package, 16 Pin QFN
C0.08
17X
ATerminal #1 mark area
BExposed thermal pad (reference only, terminal #1
identifier appearance at supplier discretion)
All dimensions nominal, not for tooling use
(reference JEDEC MO-220WEED-4)
Dimensions in millimeters
Exact case and lead configuration at supplier discretion within limits shown
CReference land pattern layout (reference IPC7351
QFN50P300X300X80-17W4M);
All pads a minimum of 0.20 mm from all adjacent pads; adjust as
necessary to meet application process requirements and PCB layout
tolerances; when mounting on a multilayer PCB, thermal vias at the
exposed thermal pad land can improve thermal dissipation (reference
EIA/JEDEC Standard JESD51-5)
16
2
1
A
16
1
2
PCB Layout Reference View
B1.70
1.70
1.70
1.70
0.30
1
16
3
3
0.75
0.25
0.50
0.40
0.50
0.90
3.10
3.10
C
D
DCoplanarity includes exposed thermal pad and terminals
3-Channel Constant-Current LED Driver
with Programmable PWM Control
A6280
13
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Copyright ©2006-2007, Allegro MicroSystems, Inc.
The products described here are manufactured under one or more U.S. patents or U.S. patents pending.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-
mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;
nor for any in fringe ment of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com