RT9058
7
DS9058-01 February 2016 www.richtek.com
©
Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Figure 1. Derating Curve of Maximum Power Dissipation
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 25 50 75 100 125
Ambient Temperature (°C)
Maximum Power Dissipation (W) 1
SOT-89-3
Four-Layer PCB
SOT-23-3
Applications Information
Like any low dropout linear regulator, the RT9058's external
input and output capacitors must be properly selected for
stability and performance. Use a 1μF or larger input
capacitor and place it close to the IC's VCC and GND pins.
Any output capacitor meeting the minimum 1mΩ ESR
(Equivalent Series Resistance) and effective capacitance
larger than 1μF requirement may be used. Place the output
capacitor close to the IC's VOUT and GND pins. Increasing
capacitance and decreasing ESR can improve the circuit's
PSRR and line transient response.
Thermal Considerations
For continuous operation, do not exceed absolute the
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and the
allowed difference between the junction and ambient
temperatures. The maximum power dissipation can be
calculated by the following formula :
P
D(MAX)
= (T
J(MAX)
− T
A
) / θ
JA
where T
J(MAX)
is the maximum junction temperature, T
A
is
the ambient temperature, and θ
JA
is the junction to ambient
thermal resistance.
The recommended operating conditions specify a
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θ
JA
, is layout dependent. On
a standard JEDEC 51-7 four-layer thermal test board ,
the thermal resistance, θ
JA
, of the SOT-23-3 package is
243.3°C/W. For the SOT-89-3 package, the θ
JA
, is
167.7°C/W. The maximum power dissipation at T
A
= 25°C
can be calculated by the following formula :
P
D(MAX)
= (125°C − 25°C) / (243.3°C/W) = 0.41W for
SOT-23-3 package
P
D(MAX)
= (125°C − 25°C) / (167.7°C/W) = 0.6W for
SOT-89-3 package
For a fixed T
J(MAX)
of 125°C, the maximum power
dissipation depends on the operating ambient temperature
and the package's thermal resistance, θ
JA
. The derating
curve in Figure 1 shows the effect of rising ambient
temperature on the maximum recommended power
dissipation.
