MC33275

http://onsemi.com

3

DEFINITIONS

Load Regulation – The change in output voltage for a

change in load current at constant chip temperature.

Dropout Voltage – 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), dropout voltage is affected

by junction temperature, load current and minimum input

supply requirements.

Output Noise Voltage – The RMS AC voltage at the

output with a constant load and no input ripple, measured

over a specified frequency range.

Maximum Power Dissipation – The maximum total

dissipation for which the regulator will operate within

specifications.

Quiescent Current – Current which is used to operate the

regulator chip and is not delivered to the load.

Line Regulation – The change in output voltage for a

change in the input voltage. The measurement is made under

conditions of low dissipation or by using pulse techniques

such that the average chip temperature is not significantly

affected.

Maximum Package Power Dissipation – The maximum

package power dissipation is the power dissipation level at

which the junction temperature reaches its maximum value

i.e. 150

°C. The junction temperature is rising while the

Depending on ambient temperature, it is possible to

calculate the maximum power dissipation and so the

maximum current as following:

Pd

+

T

J

–T

A

RqJA

specified at 150

neglecting the quiescent current, the maximum power

dissipation can be expressed as:

Iout +

P

D

V

CC

–Vout

The thermal resistance of the whole circuit can be

evaluated by deliberately activating the thermal shutdown

of the circuit (by increasing the output current or raising the

input voltage for example).

Then you can calculate the power dissipation by

subtracting the output power from the input power. All

variables are then well known: power dissipation, thermal

shutdown temperature (150

°C for MC33275) and ambient

temperature.

RqJA +

T

J

–T

A

P

D