AS1105 데이터 시트보기 (PDF) - austriamicrosystems AG

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AS1105

Serially Interfaced, 4-Digit LED Driver

austriamicrosystems AG 

Data Sheet AS1105

Computing Power Dissipation

The upper limit for power dissipation (PD) for the AS1105 is determined from the following equation:

PD = (VDD x 0.5mA) + (VDD - VLED)(DUTY x ISEG x N)

where:

VDD = supply voltage

DUTY = duty cycle set by intensity register

N = number of segments driven (worst case is 4)

VLED = LED forward voltage

ISEG = segment current set by RSET

Dissipation Example:

ISEG = 40mA, N = 4, DUTY = 31/32, VLED = 1.8V at 40mA, VDD = 5.25V

PD = 5.25V(0.5mA) + (5.25V - 1.8V)(31/32 x 40mA x 4) = 0.54W

Thus, for a SO package θJA = +85°C/W (from Table 13), the maximum allowed ambient temperature TA is given by:

TJ,MAX = TA + PD x θJA = 150°C = TA +0.54W x 85°C/W.

where TA = +104°C.

Package Information

Revision 1.32, Oct. 2004

Page 10 of 12

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