3A Ultra Low Dropout Linear Regulator
TJ4230
where T
J
is the junction temperature, T
C
is the case temperature, T
A
is the ambient temperature, P
D
is the
total power dissipation of the device,
θ
CA
is the thermal resistance of case-to-ambient,
θ
JC
is the thermal
resistance of junction-to-case, and
θ
JA
is the thermal resistance of junction to ambient.
The total power dissipation of the device is given by:
P
D
= P
IN
– P
OUT
= (V
IN
X I
IN
)–(V
OUT
X I
OUT
)
= (V
IN
X (I
OUT
+I
GND
)) – (V
OUT
X I
OUT
) = (V
IN
- V
OUT
) X I
OUT
+ V
IN
X I
GND
where I
GND
is the operating ground current of the device which is specified at the Electrical Characteristics.
The maximum allowable temperature rise (T
Rmax
) depends on the maximum ambient temperature (T
Amax
)
of the application, and the maximum allowable junction temperature (T
Jmax
):
T
Rmax
= T
Jmax
– T
Amax
The maximum allowable value for junction-to-ambient thermal resistance,
θ
JA
, can be calculated using the
formula:
θ
JA
= T
Rmax
/ P
D
TJ4230 is available in SOP8-PP, TO252 and TO263 packages. The thermal resistance depends on
amount of copper area or heat sink, and on air flow.
If proper cooling solution such as heat sink, copper plane area, or air flow is applied, the maximum
allowable power dissipation could be increased. However, if the ambient temperature is increased, the
allowable power dissipation would be decreased.
The graph above is valid for the thermal impedance specified in the Absolute Maximum Ratings section
on page 1.
Apr. 2011 – Rev. 1. 0
8/9
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
