AS2830AT-3.3 View Datasheet(PDF) - Alpha Industries

Part Name

Description

Manufacturer

AS2830AT-3.3

3A Low Dropout Voltage Regulator Adjustable & Fixed Output, Fast Response

Alpha Industries 

APPLICATION HINTS

The ALPHA Semiconductor AS2830incorporates protection

against over-current faults, reversed load insertion, over

temperature operation, and positive and negative transient

voltage. However, the use of an output capacitor is required

in order to improve the stability and the performances.

Stability

The output capacitor is part of the regulator’s frequency

compensation system. Either a 22µF aluminum electrolytic

capacitor or a 10µF solid tantalum capacitor between the

output terminal and ground guarantees stable operation for all

operating conditions.

However, in order to minimize overshoot and undershoot, and

therefore optimize the design, please refer to the section

‘Ripple Rejection’.

Ripple Rejection

Ripple rejection can be improved by adding a capacitor

between the ADJ pin and ground as shown in figure 6. When

ADJ pin bypassing is used, the value of the output capacitor

required increases to its maximum (22µF for an aluminum

electrolytic capacitor, or 10µF for a solid tantalum capacitor).

If the ADJ pin is not bypass, the value of the output capacitor

can be lowered to 10µF for an electrolytic aluminum

capacitor or 4.7µF for a solid tantalum capacitor.

However the value of the ADJ-bypass capacitor should be

chosen with respect to the following equation:

C = 1 / ( 6.28 * FR * R1 )

Where C = value of the capacitor in Farads (select an

equal or larger standard value),

FR = ripple frequency in Hz,

R1 = value of resistor R1 in Ohms.

If an ADJ-bypass capacitor is use, the amplitude of the output

ripple will be independent of the output voltage. If an ADJ-

bypass capacitor is not used, the output ripple will be

proportional to the ratio of the output voltage to the reference

voltage:

M = VOUT / VREF

Where M = multiplier for the ripple seen when the ADJ pin

is optimally bypassed.

VREF = Reference Voltage

AS2830

Reducing parasitic resistance and inductance

One solution to minimize parasitic resistance and inductance

is to connect in parallel capacitors. This arrangement will

improve the transient response of the power supply if your

system requires rapidly changing current load condition.

Thermal Consideration

Although the AS2830 offers some limiting circuitry for

overload conditions, it is necessary not to exceed the

maximum junction temperature, and therefore to be careful

about thermal resistance. The heat flow will follow the

lowest resistance path, which is the Junction-to-case thermal

resistance. In order to insure the best thermal flow of the

component, a proper mounting is required. Note that the case

of the device is electrically connected to the output. In case

the case has to be electrically isolated, a thermally conductive

spacer can be used. However do not forget to consider its

contribution to thermal resistance.

Assuming:

VIN = 10V, VOUT = 5V, IOUT = 1.5A, TA = 50°C/W,

θ Heatsink Case= 6°C/W, θ Heatsink Case = 0.5°C/W, θ JC = 3°C/W

Power dissipation under this condition

PD = (VIN – VOUT) * IOUT = 7.5W

Junction Temperature

TJ = TA + PD * (θ Case - HS+ θ HS + θ JC)

For the Control Sections

TJ = 50 + 7.5*(0.5 +6=3) = 121.25°C

121.25°C < TJ (max) for the Control & Power Sections.

In both case reliable operation is insured by adequate junction

temperature.

Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (9250 417-1391 Fax: (925) 417-1390

Rev.8/10/99

This Material Copyrighted By Its Respective Manufacturer

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