ZXCT1012
Power dissipation
The maximum allowable power dissipation of the device for normal operation (PMAX), is a
function of the package junction to ambient thermal resistance (⍜JA), maximum junction
temperature (TJMAX), and ambient temperature (Tamb), according to the expression:
PMAX = (TJMAX – Tamb) / ⍜JA
The device power dissipation, PD is given by the expression:
PD=IOUT.(VIN-VOUT) watts
Care must be taken when using this device at large input voltages and large sense voltages to
prevent too much power dissipation.
600
500
400
300
200
100
0
0
Power Dissipation
TDFN3x3-5
TSOT23-5
25
50
75 100 125 150
TA - Ambient temperature (°C)
VIN
ROUT
IOUT
VOUT
∴ PD
= 20V
= 100⍀
VSENSE = 2.5V
= 2.5 x 0.01
= 25mA
= IOUT x ROUT
= 25mA x 100⍀
= 2.5V
= 25mA (20 - 2.5)V
= 438mW
Issue 1 - December 2006
7
© Zetex Semiconductors plc 2006
www.zetex.com