spx3940am3-l-5-0-tr Exar Corporation, spx3940am3-l-5-0-tr Datasheet - Page 6

• Manufacturer Part Number: spx3940am3-l-5-0-tr
• Description: 1.0a Low Dropout Voltage Regulator
• Manufacturer: Exar Corporation

Capacitor Requirements
The output capacitor is needed to insure stability and minimize the output noise. The value of the
capacitor varies with the load. However, a minimum value of 10µF aluminum capacitor will guarantee
stability over all load conditions. A tantalum capacitor is recommended if a faster load transient
response is needed.
If the power source has a high AC impedance, a 0.1µF ceramic capacitor between input & ground is
recommended.
Minimum Load Current
To ensure a proper behavior of the regulator under light load, a minimum load of 5mA for SPX3940
is required.
Figure 18. Fixed Output Linear Regulator.
Date: 4/14/06 Rev A
The SPX3940 incorporates protection against
over-current faults, reversed load insertion, over
temperature operation, and positive and nega-
tive transient voltage.
Thermal Considerations
Although the SPX3940 offers limiting circuitry
for overload conditions, it is still necessary to
insure that the maximum junction temperature
is not exceeded in the application. Heat will
flow through the lowest resistance path, the
junction-to-case path. In order to insure the best
thermal flow of the component, proper mount-
ing is required. Consult heatsink manufacturer
for thermal resistance and design of heatsink.
V
IN
6.8µF
+
1
SPX3940 1A Low Dropout Voltage Regulator
SPX3940
2
6
For example, TO-220 design:
Assume that V
T
θ
Where TA = ambient temperature
θ
θ
θ
The power calculated under these conditions is:
P
T
T
Reliable operation is insured.
And the junction temperature is calculated as
JC
HA
CH
JC
D
A
J
J
= T
= 50 + 7.5 * (1 + 2 + 3) = 95°C
= (V
= 50°C/W, θ
= 3°C/W.
= junction to case thermal resistance
= case to heatsink thermal resistance
= heatsink to ambient thermal resistance
3
A
IN
+ P
- V
APPLICATION INFORMATION
D
OUT
* (θ
+
IN
10µF
HA
) * I
= 10V, V
HA
= 1°C/W, θ
OUT
+ θ
V
© Copyright 2006 Sipex Corporation
CH
OUT
= 7.5W.
OUT
+ θ
= 5V, I
CH
JC
) or
= 2°C/W, and
OUT
= 1.5A,