SPX3940 Datasheet, PDF (6/11 Pages) Sipex Corporation – 1A Low Dropout Voltage Regulator Fixed Output, Fast Response

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.
APPLICATION INFORMATION
For example, TO-220 design:
Assume that V = 10V, V = 5V, I = 1.5A,
IN
OUT
OUT
T
A
=
50°C/W,
θ_HA=
1°C/W,
θ_CH
=
2°C/W,
and
θ_JC = 3°C/W.
Where TA = ambient temperature
θ_HA = heatsink to ambient thermal resistance
θ_CH = case to heatsink thermal resistance
θ_JC = junction to case thermal resistance
The power calculated under these conditions is:
P_D = (V_IN - V_OUT) * I_OUT = 7.5W.
And the junction temperature is calculated as
T_J = T_A + P_D * (θ_HA + θ_CH + θ_JC) or
T
J
=
50
+
7.5
*
(1
+
2
+
3)
=
95°C
Reliable operation is insured.
V_IN
6.8µF+
1 ^SPX3940 3
2
V_OUT
+10_µF
Figure 18. Fixed Output Linear Regulator.
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.
Date: 5/25/04
SPX3940 1A Low Dropout Voltage Regulator
6
© Copyright 2004 Sipex Corporation