SC560 SEMTECH [Semtech Corporation], SC560 Datasheet - Page 12

• Manufacturer Part Number: SC560
• Description: Dual Output Low Noise LDO Linear Regulator
• Manufacturer: SEMTECH [Semtech Corporation]

Applications Information (continued)
Thermal Considerations
Although each of the two LDOs in the SC560 can provide
300mA of output current, the maximum power dissipation
in the device is restricted by the miniature package size.
The graphs in Figure 3 and Figure 4 can be used as a
guideline to determine whether the input voltage, output
voltages, output currents, and ambient temperature of the
system result in power dissipation within the operating
limits are met or if further thermal relief is required.
0.6
0.7
0.5
0.4
0.3
0.2
1.4
0.8
0.2
1.2
0.6
0.4
0.1
1.6
0
1
0
2.5
-40
______
- - - - T
T
A
A
=+25
=+85
-20
3
Figure 3 — Safe Operating Limit
Vo=1.5V
Figure 4 — Maximum P
°
°
C, P
C, P
D(MAX)
D(MAX)
3.5
0
= 0.8W
= 0.41W
Ambient Temperature (
T
T
J
J
Input Voltage (V)
(Max)=125
(Max)=150
20
4
°
°
C
C
4.5
40
Vo=3.3V
o
C)
D
5
60
vs. T
A
5.5
80
100
6
The following procedure can be followed to determine if
the thermal design of the system is adequate. The junction
temperature of the SC560 can be determined in known
operating conditions using the following equation:
where
Example
An SC560D is used to provide outputs of 2.8V, 150mA from
LDOA and 1.8V, 200mA from LDOB. The input voltage is
4.2V, and the ambient temperature of the system is 40°C.
and
Figures 3 and 4 show that the junction temperature
would be within the maximum specifi cation of 150°C
for this power dissipation. This means that operation of
the SC560 under these conditions is within the specifi ed
limits and the device would not require further thermal
relief measures.
T
T
T
P
θ
P
T
A
J
J
J
D
JA
D
= 40 + (0.69 x 157) = 148.3°C
= T
= Junction Temperature (°C)
= 0.15(4.2 – 2.8) + 0.2(4.2 – 1.8)
= 0.69W
= Ambient Temperature (°C)
= Power Dissipation (W)
= Thermal Resistance Junction to Ambient (°C/W)
A
+(P
D
x θ
JA
)
SC560
12