SP6231 datasheet(6/10 Pages) SIPEX

6 / 10 page

Date: 5/25/04

SP6231 500mA, 3.3V Linear Regulator

TYPICAL PERFORMANCE CHARACTERISTICS: continued

Figure 9. Supply Switching under full load, Vaux=3.3V.

Ch 1=Vin; Ch 2=Vout; Ch 3=Iload (500mA/div).

Figure 8. Load transients. 1 - VOUT, 4 - ILOAD (500mA/div)

Input Capacitor

A small capacitor 2.2

µF or higher, is required

from VIN to GND and VAUX to GND to create a

high frequency bypass for the LDO amplifier.

Any ceramic or tantalum capacitor may be used

at the inputs. Capacitor ESR (equivalent series

resistance) should be smaller than 1

Ω.

Output Capacitor

An output capacitor is required between VOUT

and GND to prevent oscillations. A 2.2

µF ca-

pacitor ensures unconditional stability from no

load to full load over the entire input voltage and

temperature range. Larger capacitor values im-

prove the regulator’s transient response. The

output capacitor value may be increased with-

out limit. The output capacitor should have an

ESR below 3

Ω and a resonant frequency above

1MHz.

Thermal Considerations

The SP6231 is designed to provide 500mA of

continuous current. Maximum power dissipa-

tion can be calculated based on the output cur-

rent and voltage drop across the device. To

determine the maximum power dissipation in

the package, use the junction-to-ambient ther-

mal resistance of the device and the following

basic equation:

PD(max) = (TJ(max) - TA) / θJA

TJ(max) is the maximum junction temperature of

the die and is 125

°C. TA is the ambient operating

temperature.

θJA is the junction-to-ambient ther-

mal resistance for the regulator and is layout and

package dependent.

The actual power dissipation of the regulator

circuit can be determined using one simple

equation:

PD = (VIN - VOUT) * IOUT + VIN * IGND

≅ (VIN - VOUT) * IOUT

Substituting PD(max) for PD and solving for the

operating conditions that are critical to the ap-

plication gives the maximum operating condi-

tions for the regulator circuit. For example if we

are operating the SP6231 at room temperature,

with a minimum footprint layout, we can deter-

mine the maximum input voltage for a set output

current.

PD(max) = (125°C - 25°C) / 57°C/W = 1754mW

(

θJA = 57°C/W for the 3x3 MLP package)

Notice that the LDO in the MLP package has a

much smaller

θJA than in comparable dimen-

sions. For comparison,

θJA = 220°C/W for a

SOT-23 package.

APPLICATION INFORMATION

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