XRP29302 Datasheet, PDF (6/9 Pages) Exar Corporation – 3A Low Dropout Voltage Regulator

THEORY OF OPERATION
The XRP29302 incorporates protection against
over-current faults, reversed load insertion,
over temperature operation, and positive and
negative transient voltage.
THERMAL CONSIDERATIONS
Although the XRP29302 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:
Assume that V_IN = 10V, V_OUT = 5V,
I_OUT = 1.5A, T_A = 50°C, θ_HA= 1°C/W, θ_CH=
2°C/W, and θ_JC= 3C°/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} = 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.
XRP29302
3A Low Dropout Voltage 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 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
XRP29302 is required.
ADJUSTABLE REGULATOR DESIGN
The XRP29302 is an adjustable regulator that
can be programmed to any value between
1.25V and 16V using 2 external resistors, R1
and R2. The relationship between the resistors
and the output voltage is:
𝑅₁ = 𝑅₂ × �₁^𝑉_.^í µ₂^í±‚í µ₄^í±ˆí µ₀^í±‡ − 1�
ENABLE INPUT
The XRP29302 has an Enable function that
switches the regulator on and off. Their
thresholds are TTL compatible. When the
regulator is active, approximately 20 µA flows
through the Enable pin.
TYPICAL APPLICATION CIRCUITS
Figure 1 represents the typical implementation
for an adjustable output regulator. The values
of R1 and R2 set the output voltage value as
follows:
𝑉_{𝑂𝑈𝑇} = 𝑉_{𝑅𝐸𝐹} × �1 + _{í µí µí±…í±}¹²ï¿½
A minimum value of 10kohms is recommended
for R2 with a range between 10kΩ and 47kΩ.
© 2013 Exar Corporation
6/9
Rev. 1.3.0