AS1107PL datasheet(14/20 Pages) AMSCO

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AS1106, AS1107

austriamicrosystems

Data Sheet

Calculating Power Dissipation

The upper limit for power dissipation (PD) for the AS1106/AS1107 is determined from the following equation:

PD = (VDD x 1mA) + (VDD - VLED)(DUTY x ISEG x N)

(EQ 1)

Where:

VDD is the supply voltage.

DUTY is the duty cycle set by intensity register (page 11).

N is the number of segments driven (worst case is 8)

VLED is the LED forward voltage

ISEG = segment current set by RSET

Dissipation Example:

ISEG = 40mA, N = 8, DUTY = 31/32, VLED = 1.8V at 40mA, VDD = 5.25V

(EQ 2)

PD = 5.25V(1mA) + (5.25V - 1.8V)(31/32 x 40mA x 8) = 1.075W

(EQ 3)

Thus, for a PDIP package

ΘJA = +75°C/W (from Table 23), the maximum allowed TAMB is given by:

TJ,MAX = TAMB + PD x

ΘJA = 150°C = TAMB +1.07W x 75°C/W

(EQ 4)

Where:

TAMB = +69.4°C.

The TAMB limit for SO Packages in the dissipation example above is +58.6°C.

17.7k

17.3k

16.6k

15.6k

13.6k

36.89k

35.7k

34.5k

32.5k

29.1k

Table 22. RSET vs. Segment Current and LED Forward Voltage, VDD = 5.0V

ISEG (mA)

VLED (V)

1.5

2.0

2.5

3.0

3.5

4.0

11.35k

11.12k

10.84k

10.49k

10.2k

9.9k

15.4k

15.1k

14.7k

14.4k

13.6k

13.1k

23.6k

23.1k

22.6k

22k

21.1k

20.2k

48.9k

47.8k

46.9k

45.4k

43.8k

42k

Table 23. Package Thermal Data

Package

Thermal Resistance (

ΘJA)

24 Narrow DIP

+75°C/W

24 Wide SOIC

+85°C/W

Table 21. RSET vs. Segment Current and LED Forward Voltage, VDD = 4.0V (Continued)

ISEG (mA)

VLED(V)

1.5

2.0

2.5

3.0

3.5

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