MAX6970AUE Maxim Integrated Products, MAX6970AUE Datasheet - Page 8

• Manufacturer Part Number: MAX6970AUE
• Description: LED Drivers 8-Port 36V Constant- t-Current LED Driver
• Manufacturer: Maxim Integrated Products

Specifications of MAX6970AUE

• Number Of Segments: 16
• Low Level Output Current: 60000 uA
• Operating Supply Voltage: 3 V to 5.5 V
• Maximum Supply Current: 30000 uA
• Maximum Power Dissipation: 1702 mW
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: TSSOP EP
• Minimum Operating Temperature: - 40 C

8-Port, 36V Constant-Current LED Driver
Selecting External Component R
The MAX6970 uses an external resistor R
LED current for outputs OUT0 to OUT7. The minimum
allowed value of R
currents up to 55mA. The reference value, 360Ω, sets
the output currents to 50mA. To set a different output
current, use the formula:
where I
The upper limit for power dissipation (P
MAX6970 is determined from 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
Figure 3. LE and CLK to OUT_ Timing
8
OUT_
LE
OUT_
LE
CLK
OUT_
CLK
OUT_
_______________________________________________________________________________________
P
OUT
D
= (V+ x I+) + (V
is the desired output current in mA.
Applications Information
R
Computing Power Dissipation
SET
SET
t
t
LRF
t
LRR
CRF
is 327.3Ω, which sets the output
= 18,000 / I
t
CRR
OUT
x DUTY x I
LED Output Current
OUT
OUT
SET
SET
D
x N)
to set the
OUT
) for the
to Set
LED
N = number of MAX6970 outputs driving LEDs at the
same time (maximum is eight)
V
LED(s)
I
P
Dissipation example:
Thus, for a 16-pin TSSOP package (T
+46.95°C/W from the Absolute Maximum Ratings), the
maximum allowed ambient temperature T
so T
The MAX6970 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds approximately +165°C. The outputs are re-
enabled again when the die temperature drops below
approximately +140°C. Register contents are not
affected, so when a driver is overdissipating, the exter-
nal symptom is the load LEDs cycling between on and
off as the driver repeatedly overheats and cools, alter-
nately turning the LEDs off and then back on again.
The MAX6970 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 MAX6970 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 four to 16 MAX6970s.
The necessary capacitance depends on the LED load
current, PWM switching frequency, and serial-interface
speed. Inadequate V+ decoupling can cause timing
problems, and very noisy LED supplies can affect LED
current regulation.
PROCESS: BiCMOS
I
OUT
OUT
P
OUT
D
T
D
J(MAX)
= power dissipation, in mW if currents are in mA.
= (5.25V x 25mA) + (2V x 1 x 50mA x 8) = 0.931W.
A
= LED drive current programmed by R
= 50mA, N = 8, DUTY = 1, V
= MAX6970 port output voltage when driving load
= +106.3°C.
= T
46.95°C/W)
A
+ (P
Power-Supply Considerations
D
x T
JA
Overtemperature Cutoff
) = +150°C = T
Chip Information
OUT
JA
= 2V, V+ = 5.25V
A
= 1 / 0.0213 =
is given by:
A
+ (0.931 x
SET