MAX6983 Maxim Integrated Products, MAX6983 Datasheet - Page 9

• Manufacturer Part Number: MAX6983
• Description: 36V Constant-Current LED Driver
• Manufacturer: Maxim Integrated Products

Table 1. 4-Wire Serial-Interface Truth Table
L = Low-logic level; H = High-logic level; X = Don’t care; P = Present state; R = Previous state.
Selecting External Component R
The MAX6983 uses an external resistor, R
LED current for outputs OUT0–OUT15. The minimum
allowed value of R
currents to 55mA. The maximum allowed value of R
is 5kΩ. The reference value, 360Ω, sets the output cur-
rents to 50mA. To set a different output current, use the
formula:
where I
The upper limit for power dissipation (P
MAX6983 is determined by the following equation:
where:
V+ = supply voltage
I+ = operating supply current when sinking I
drive current into N outputs
DUTY = PWM duty cycle applied to OE
N = number of MAX6983 outputs driving LEDs at the
same time (maximum is 16)
V
LED(s)
I
P
Dissipation example:
SERIAL
OUT
INPUT
OUT
D
DATA
DIN
—
—
—
= power dissipation, in mW if currents are in mA
16-Port, 36V Constant-Current LED Driver with
H
X
L
= LED drive current programmed by R
= MAX6983 port output voltage when driving load
P
OUT
D
CLOCK
INPUT
= (V+ x I+) + (V
CLK
—
—
—
is the desired output current in mA.
Applications Information
R
D
Computing Power Dissipation
R
P
—
H
L
X
_______________________________________________________________________________________
SET
SET
0
0
1
SHIFT REGISTER
D
R
R
R
P
—
X
is 327.3Ω, which sets the output
= 18,000 / I
1
1
1
2
1
CONTENTS
OUT
D
R
R
R
P
—
X
2
2
2
2
3
x DUTY x I
LED Output Current
… D
… R
… R
… R
…
… P
—
LED Fault Detection and Watchdog
OUT
—
n-1
n-2
n-2
n-1
n-1
X
R
R
D
R
P
—
OUT
n-1
n-1
X
n
n
n
SET,
SET
SET
INPUT
LOAD
D
x N)
LE
—
—
—
—
H
to set the
OUT
L
) for the
to Set
LED
D
R
P
SET
—
—
—
X
0
0
0
LATCH CONTENTS
D
R
P
—
—
—
X
1
1
1
Thus, for a 24-pin TSSOP package (T
+82°C/W from the Absolute Maximum Ratings), the
maximum allowed ambient temperature T
so T
The MAX6983 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds approximately +165°C. The outputs are
enabled again when the die temperature drops below
approximately +140°C. Register contents are not affect-
ed, so when a driver is overdissipating, the external
symptom is the load LEDs cycling between on and off as
the driver repeatedly overheats and cools, alternately
turning the LEDs off and then back on again.
The MAX6983 operates with a chip supply V+, and one
or more LED supplies. Bypass each supply to GND
with a 0.1µF capacitor as close to the MAX6983 as pos-
sible. This is normally adequate for static LED driving.
For multiplex or PWM applications, it is necessary to
add an additional bulk electrolytic capacitor of 4.7µF or
more to each supply for every 4 to 16 MAX6983s. The
necessary capacitance depends on the LED load cur-
rent, PWM switching frequency, and serial interface
speed. Inadequate V+ decoupling can cause timing
problems, and very noisy LED supplies can affect LED
current regulation.
D
R
—
—
—
P
X
P
2
2
2
D
A
= (5.25V x 25mA) + (2V x 1 x 20mA x 16) = 0.77W
… D
—
—
—
… P
…
= +85°C.
T
R
—
—
—
J(MAX)
n-1
n-1
n-1
X
I
OUT
D
R
—
—
—
P
X
n
n
n
= 20mA, N = 16, DUTY = 1,
= T
Power-Supply Considerations
BLANKING
V
T
INPUT
OUT
A
A
OE
—
—
—
—
+ (P
H
L
+ (0.77 x 82°C/W)
Overtemperature Cutoff
= 2V, V+ = 5.25V
D
x T
Hi-Z Hi-Z Hi-Z … Hi-Z Hi-Z
D
P
—
—
—
—
0
0
JA
OUTPUT CONTENTS
) = +150°C =
D
P
—
—
—
—
1
1
JA
D
P
—
—
—
—
www.DataSheet4U.com
2
2
= 1 / 0.0122 =
A
is given by:
… D
—
—
—
—
… P
—
—
—
—
n-1
n-1
D
P
—
—
—
—
n
n
9