MAX6968AUE Maxim Integrated Products, MAX6968AUE Datasheet - Page 9

• Manufacturer Part Number: MAX6968AUE
• Description: LED Drivers 8-Port, 5.5V LED Dri ver, 8-Segment Any d
• Manufacturer: Maxim Integrated Products

Specifications of MAX6968AUE

• Number Of Segments: 16
• Low Level Output Current: 60000 uA
• Operating Supply Voltage: 3 V to 5.5 V
• Maximum Supply Current: 25000 uA
• Maximum Power Dissipation: 1702 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: TSSOP EP
• Minimum Operating Temperature: - 40 C

The MAX6968 uses an external resistor R
LED current for outputs OUT0–OUT7. The minimum
allowed value of R
currents to 55mA. The maximum allowed value of R
is 1.5kΩ. 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
MAX6968 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 MAX6968 outputs driving LEDs at the
same time (maximum is 8)
V
LED(s)
I
P
Dissipation example:
I
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
Selecting External Component R
OUT
OUT
P
OUT
D
D
= power dissipation, in mW if currents are in mA
A
= (5.25V x 25mA) + (2V x 1 x 47mA x 8) = 0.883W
= LED drive current programmed by R
= 47mA, N = 8, DUTY = 1, V
= MAX6968 port output voltage when driving load
= +108.5°C.
P
OUT
D
T
= (V+ x I+) + (V
J(MAX)
is the desired output current in mA.
Applications Information
= T
8-Port, 5.5V Constant-Current LED Driver
R
Computing Power Dissipation
_______________________________________________________________________________________
SET
SET
T
A
A
+ (0.883 x 46.95°C/W)
+ (P
is 307.6Ω, which sets the output
= 18,000 / I
OUT
D
x T
x DUTY x I
LED Output Current
JA
) = +150°C =
OUT
OUT
JA
= 2V, V+ = 5.25V
OUT
= 1 / 0.0213 =
A
SET
SET
is given by:
SET
D
x N)
to set the
OUT
) for the
to Set
LED
SET
The MAX6968 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
affected, so when a driver is overdissipating, the exter-
nal symptom will be 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 MAX6968 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 MAX6968 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 MAX6968s. 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.
For the TSSOP version, connect the underside exposed
pad to GND.
TRANSISTOR COUNT: 2382
PROCESS: BiCMOS
Power-Supply Considerations
Overtemperature Cutoff
Chip Information
9