AS1105 datasheet(10/12 Pages) AMSCO

Part #	AS1105

Description	Serially Interfaced, 4-Digit LED Driver

PDF	12 Pages

Scroll/Zoom	100%

Manufacturer	AMSCO [ams AG]

Direct Link	http://www.ams.com

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10 / 12 page

Data Sheet AS1105

Revision 1.32, Oct. 2004

Page 10 of 12

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

AS1105 Datasheet(PDF) 10 Page - ams AG