Datasheet

LM2937
SNVS100E –MARCH 2000–REVISED APRIL 2013 www.ti.com
If two capacitors are paralleled, the effective ESR is the parallel of the two individual values. The “flatter” ESR of
the Tantalum will keep the effective ESR from rising as quickly at low temperatures.
HEATSINKING
A heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of
the application. Under all possible operating conditions, the junction temperature must be within the range
specified under Absolute Maximum Ratings.
To determine if a heatsink is required, the power dissipated by the regulator, P
D
, must be calculated.
The figure below shows the voltages and currents which are present in the circuit, as well as the formula for
calculating the power dissipated in the regulator:
I
IN
= I
L
+ I
G
P
D
= (V
IN
− V
OUT
) I
L
+ (V
IN
) I
G
Figure 25. Power Dissipation Diagram
The next parameter which must be calculated is the maximum allowable temperature rise, T
R
(max). This is
calculated by using the formula:
T
R
(max) = T
J
(max) − T
A
(max)
where
• T
J
(max) is the maximum allowable junction temperature, which is 125°C for commercial grade parts
• T
A
(max) is the maximum ambient temperature which will be encountered in the application (1)
Using the calculated values for T
R
(max) and P
D
, the maximum allowable value for the junction-to-ambient
thermal resistance, θ
(J−A)
, can now be found:
θ
(J−A)
= T
R
(max)/P
D
(2)
IMPORTANT: If the maximum allowable value for θ
(J−A)
is found to be ≥ 53°C/W for the TO-220 package, ≥
80°C/W for the DDPAK/TO-263 package, or ≥174°C/W for the SOT-223 package, no heatsink is needed since
the package alone will dissipate enough heat to satisfy these requirements.
If the calculated value for θ
(J−A)
falls below these limits, a heatsink is required.
10 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated
Product Folder Links: LM2937