Philips Semiconductors

Product data

SA57003

Five-output composite voltage regulator

2003 Oct 13

13

generated heat. Heat dissipation must depend primarily on radiated

heat into the surrounding environment and the heat flow through the

leads into the printed circuit board. Some improvement can be

realized by allowing additional exposed copper on the circuit board

near the device to serve as heat absorbers and dissipaters for the

device.

The overall thermal resistance from junction to the surrounding

and can be thought of as the total resistance of a series electrical

circuit. These elements are:

silicon chip used in the device. The composition of package

materials plays an important part. High heat conductivity materials

produce reduced Junction-to-Case resistances.

contact area of the device to the heat sink. The use of thermal

grease or an insulator will increase the transfer of heat from the

case to the heat sink.

based on heat sink emissivity and airflow over the heat sink to carry

the heat away. The heat sink to ambient heat flow is dependent on

the ability of the surrounding ambient media to absorb the heat.

The maximum power that a given package can handle is given by:

P

T

R

th(j

*a)

DEFINITIONS

Line regulation is the change in output voltage caused by a change

in input line voltage. This parameter is measured using pulse

measurement techniques or under conditions of low power

dissipation so as to not significantly upset the thermal dynamics of

the device during test.

Load regulation is the change in output voltage caused by a

change in output load current for a constant device temperature.

Quiescent current is that current which flows to the ground pin of

the device when the device is operated with no load.

Ground current is that current which flows to the ground pin of the

device when the device is operated with output current flowing due

to an applied load. It is the measurement difference of input current

minus the output current.

Dropout voltage is the input/output differential at which the

regulator output no longer maintains regulation against further

reductions in input voltage. Measured when the output drops

100 mV below its nominal value (which is measured at 1.0 V

differential input/output), dropout voltage is affected by junction

temperature, load current and minimum input supply requirements.

Output noise voltage is the integrated output noise voltage

(RMS AC) specified over a frequency range and expressed in

no input ripple.

Current limiting is internal device circuitry incorporated to limit the

output current of the device. This feature is incorporated in the

device to protect the device against output over current conditions or

output shorts to ground.

Thermal shutdown is internal device circuitry incorporated in the

device to shut down the device when the chip temperature reaches

a specified temperature. This feature protects the device from

excessive operating temperatures that would otherwise be

catastrophic to the device. Over heating can be created by

accidental output shorts.

Maximum power dissipation is the maximum total dissipation for

which the regulator will operate within specifications.