MC33275, NCV33275
www.onsemi.com
4
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
difference between the input power (V
CC
X I
CC
) and the
output power (V
out
X I
out
) is increasing.
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
R
JA
The maximum operating junction temperature T
J
is
specified at 150°C, if T
A
= 25°C, then P
D
can be found. By
neglecting the quiescent current, the maximum power
dissipation can be expressed as:
I
out
+
P
D
V
CC
* V
out
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 and ambient temperature.
R
JA
+
T
J
* T
A
P
D
