SP6205EM5-L-3-3-TR Datasheet, PDF (10/15 Pages) Exar Corporation – 300mA/500mA Low Noise CMOS LDO Regulators

SP6203 / SP6205
300mA/500mA Low Noise CMOS LDO Regulators
time (T_WU) and the settling time (T_S). The
wake up time is defined as the time it takes
for the output to rise to 2% of its total value
after being released from shutdown (E_N >
0.4V). The settling time is defined as the
condition where the output reaches 98% of its
total value after being released from
shutdown. The latter is also called the turn on
time and is dependent on the output capacitor,
a little bit on load and, if present, on a bypass
capacitor.
TURN OFF TIME
The turn off time is defined as the condition
where the output voltage drops about 66% (θ)
of its total value. 5θ to 7θ is the constant
where the output voltage drops nearly to zero.
There will always be a small voltage drop in
shutdown because of the switch unless we
short-circuit it. The turn off time of the output
voltage is dependent on load conditions,
output capacitance on V_OUT (time constant  =
R_LC_L) and also on the difference in voltage
between input and output.
THERMAL CONSIDERATIONS
The SP6203/6205 is designed to provide
300/500mA of continuous current in a tiny
package. Maximum power dissipation can be
calculated based on the output current and the
voltage drop across the part. To determine the
maximum power dissipation of the package,
use the junction-to-ambient thermal
resistance of the device and the following
basic equation:
P_D = (T_J(max) - T_A) / θ_JA
T_J(max) is the maximum junction temperature of
the die and is 125°C. T_A is the ambient
temperature. θ_JA is the junction-to-ambient
thermal resistance for the regulator and is
layout dependent. The SOT-23-5 package has
a θ_JA of approximately 191°C/W for minimum
PCB copper footprint area.
This results in a maximum power dissipation
of:
P_D(max)=[(125°C-25°C)/(191°C/W)] = 523mW
The actual power dissipation of the regulator
circuit can be determined using one simple
equation:
P_D = (V_IN - V_OUT) * I_OUT + V_IN * I_GND
To prevent the device from entering thermal
shutdown, maximum power dissipation cannot
be exceeded.
Substituting P_D(max) for P_D and solving for the
operating conditions that are critical to the
application will give the maximum operating
conditions for the regulator circuit. For
example, if we are operating the SP6203 3.0V
at room temperature, with a minimum
footprint layout and output current of 300mA,
the maximum input voltage can be
determined, based on the equation below.
Ground pin current can be taken from the
electrical specifications table (0.23mA at
300mA).
390mW = (V_IN-3.0V) * 300mA + V_IN *0.23mA
After calculations, we find that the maximum
input voltage of a 3.0V application at 300mA
of output current in a SOT-23-5 package is
4.7V.
So if the intent is to operate a 5V output
version from a 6V supply at 300mA load and
at a 25°C ambient temperature, then the
actual total power dissipation will be:
P_D=([6V-5V]*[300mA])+(6V*0.23mA)=301.4mW
This is well below the 523mW package maxi-
mum. Therefore, the regulator can be used.
Note that the regulator cannot always be used
at its maximum current rating. For example, in
a 5V input to 3.0V output application at an
ambient temperature of 25°C and operating at
the full 500mA (I_GND=0.355mA) load, the
regulator is limited to a much lower load
current, determined by the following equation:
523mW = ( [5V-3V]*[ I_load(max)]) +(5V*0.350mA)
© 2012 Exar Corporation
10/14
Rev. 2.0.0