APPLICATION INFORMATION
The SPX29501/02 incorporates protection
against over-current faults, reversed load
insertion, over temperature operation, and
positive
and negative transient voltage.
Thermal Considerations
load transient response is needed. If the power
source has a high AC impedance, a 0.1µF ce-
ramic capacitor between input & ground is rec-
ommended.
Minimum Load Current
Although the SPX29501/02 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
mounting is required.
TO-220 Design Example:
To ensure a proper behavior of the regulator
under light load, a minimum load of 10mA for
SPX29501/02 is required.
Adjustable Regulator Design
The SPX29502
is an
adjustable regulator that
can be programmed to any value between 1.24V
and 16V using 2 resistors, R1 and R2. The
relationship between the resistors is:
R1 = R2(V
OUT
/1.24-1).
Error Flag
Assume that V
IN
= 8V, V
OUT
= 5V, I
OUT
= 5A, T
A
= 50°C,
θ
HA
= 1°C/W,
θ
CH
= 2°C/W, and
θ
JC
=
2°C/W, where:
T
A
= 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
= 15W.
And the junction temperature is calculated as
T
J
= T
A
+ P
D
* (θ
HA
+
θ
CH
+
θ
JC
) or
T
J
= 50 + 15 * (1+2+2) = 125°C
Reliable operation is insured.
Capacitor Requirements
The SPX29501 features an error flag that
indicates either an over current or under voltage
condition. The flag output goes low, sinking
10mA when either condition occurs.
Enable Input
The SPX29501/02 have an Enable function that
switches the regulator on and off. Their thresh-
olds are TTL compatible. Enabling the regulator
requires approximately 20µA of current.
Typical Application Circuits
Figure 1 represents at typical fixed output regu-
lator. Figure 2 represents an adjustable output
regulator. The values of R1 and R2 set the output
voltage value as follows:
V
OUT
=V
REF
* [1 + (R1/R2)].
For best results, the total series resistance should
guarantee a minimum regulator load current of
10mA.
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 22µF aluminum capacitor
will guarantee stability over all load conditions.
A tantalum capacitor is recommended if a faster
Rev:B
Nov 2008
SPX29500/01/02/03 5A Low Dropout Voltage Regulator
©
Copyright 2008
Exar
Corporation
5
EXAR [ EXAR CORPORATION ]
