AS1360
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9 Application Information
Figure 14. AS1360 - Typical Application Diagram
+9V
Alkaline
Battery
3
C
IN
1µF
*
V
IN
AS1360
2
V
OUT
C
OUT
1µF
*
V
OUT
= 3.3V
GND
*
1
Tantalum Capacitor
Power Dissipation
Power dissipation (PD) of the AS1360 is the sum of the power dissipated by the p-channel MOSFET and the quiescent
current required to bias the internal voltage reference and the internal power amplifier, and is calculated as:
PD (P-Channel MOSFET) = (V
IN
- V
OUT
)I
OUT
(EQ 1)
Internal power dissipation as a result of the bias current for the internal voltage reference and the error amplifier is cal-
culated as:
PD (Bias) =
V
IN
I
GND
Total AS1360 power dissipation is calculated as:
PD(Total) = PD (P-Channel MOSFET) + PD (Bias)
(EQ 3)
The internal quiescent bias current (2µA, typ) is such that the PD(Bias) term of (EQ 3) can be disregarded and the
maximum power dissipation can be estimated using V
IN(MAX)
and V
OUT(MIN)
to obtain a maximum voltage differential
between V
IN
and V
OUT
, and multiplying the maximum voltage differential by the maximum output current:
PD = (V
IN(MAX)
V
OUT(MIN)
)I
OUT(MAX)
Where:
V
IN
= 3.3 to 4.1V
V
OUT
= 3.0V ±2%
I
OUT
= 1 to 100mA
T
AMB(MAX)
= 55ºC
P
MAX
= (4.1V - (3.0V x 0.98)) x 100mA = 116.0mW
(EQ 4)
(EQ 2)
Junction Temperature
The AS1360 junction temperature (T
J
) can be determined by first calculating the thermal resistance from junction tem-
perature-to-ambient temperature.
Note:
Thermal resistance is estimated to be the junction temperature-to-air temperature R
ΦJA
, and is approximately
230°C/W or 335ºC/W (when mounted on 1 square inch of copper). R
ΦJA
will vary depending on PCB layout,
air-flow and application specific conditions.
The AS1360 junction temperature is determined by calculating the rise in T
J
above T
AMB
, and then adding the increase
of T
AMB
:
T
J
= P
D(MAX)
x R
Φ
JA
+
T
AMB
From (EQ 5), the value of T
J
can be calculated as:
T
J
= 116.0mW x 230ºC/W + 55ºC
Therefore:
T
J
= 81.68ºC
(EQ 5)
Revision 1.04
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