SP6231 Datasheet, PDF (6/10 Pages) Sipex Corporation – 500mA, 3.3V Linear Regulator with Auxiliary Backup

TYPICAL PERFORMANCE CHARACTERISTICS: continued
Figure 8. Load transients. 1 - V_OUT, 4 - I_LOAD (500mA/div)
Figure 9. Supply Switching under full load, Vaux=3.3V.
Ch 1=Vin; Ch 2=Vout; Ch 3=Iload (500mA/div).
Input Capacitor
A small capacitor 2.2µF or higher, is required
from V_IN to GND and V_AUX 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 1Ω.
Output Capacitor
An output capacitor is required between V_OUT
and GND to prevent oscillations. A 2.2µF 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 3Ω 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:
P_D(max) = (T_J(max) - T_A) / θ_JA
APPLICATION INFORMATION
T_J(max) is the maximum junction temperature of
the die and is 125°C. T_A is the ambient operating
temperature. θ_JA 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 = (V_IN - V_OUT) * I_OUT + V_IN * I_GND
≅ (V_IN - V_OUT) * I_OUT
Substituting P_D(max) for P_D 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.
P_D(max) = (125°C - 25°C) / 57°C/W = 1754mW
(θ_JA = 57°C/W for the 3x3 MLP package)
Notice that the LDO in the MLP package has a
much smaller θ_JA than in comparable dimen-
sions. For comparison, θ_JA = 220°C/W for a
SOT-23 package.
Date: 5/25/04
SP6231 500mA, 3.3V Linear Regulator
6
© Copyright 2004 Sipex Corporation