SC1458 SEMTECH [Semtech Corporation], SC1458 Datasheet - Page 10

• Manufacturer Part Number: SC1458
• Description: Dual Output Low Noise LDO Linear Regulator
• Manufacturer: SEMTECH [Semtech Corporation]

Applications Information (continued)
until the fault is removed and the load current returns to
a specifi ed level.
Component Selection
A capacitance of 1μF or larger on each output is
recommended to ensure stability. Ceramic capacitors
of type X5R or X7R should be used because of their
low ESR and stable temperature coeffi cients. It is also
recommended that the input be bypassed with a 2.2μF,
low ESR X5R or X7R capacitor to minimize noise and
improve transient response. Note: Tantalum and Y5V
capacitors are not recommended.
A
connected between the BYP and GND pins to meet all
noise-sensitive requirements. Increasing the capacitance
to 100nF will further improve PSRR and output noise
(SC1458B only).
Thermal Considerations
Although each of the two LDOs in the SC1458 can
provide 300mA of output current, the maximum power
dissipation in the device is restricted by the miniature
package size. The graphs in Figure 2 and Figure 3 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 or if further thermal relief is
required.
0.6
0.5
0.4
0.3
0.2
0.1
0
bypass capacitor (minimum of 22nF) should be
3
______
- - - - T
T
A
A
=+25°C, P
=+85°C, P
Figure 2 — Safe Operating Limit
3.5
D(MAX)
D(MAX)
4
= 1.9W
= 1.0W
Input Voltage (V)
4.5
5
5.5
6
T
the thermal design of the system is adequate. The junction
temperature of the SC1458 can be determined in known
operating conditions using the following equation:
where
Example
An SC1458A is used to provide outputs of 2.5V, 150mA
from LDOA and 1.8V, 200mA from LDOB. The input
voltage is 4.2V, and the ambient temperature of the
system is 60°C.
and
Figure 3 shows that the power dissipation is within limits
at T
specifi ed limit of 150°C.
This means that operation of the SC1458 under these
conditions is within the specifi ed limits and the device
would not require further thermal relief measures.
he following procedure can be followed to determine if
1.8
1.5
1.2
0.9
0.6
0.3
T
T
T
P
θ
P
T
0
A
A
J
J
J
D
JA
D
-40
= 60 + (0.74 x 50) = 97°C
= 60°C and calculation of T
= T
= Junction Temperature (°C)
= 0.15(4.2 – 2.5) + 0.2(4.2 – 1.8)
= 0.74W
= Ambient Temperature (°C)
= Power Dissipation (W)
= Thermal Resistance Junction to Ambient (°C/W)
A
+(P
-20
D
Figure 3 — Maximum P
x θ
JA
)
0
Ambient Temperature (
20
T
J
(Max)=125
J
shows that it is within the
40
°
C
o
C)
D
vs. T
60
T
J
(Max)=150
A
SC1458
80
°
C
100
10