SP6203_07 Datasheet, PDF (10/16 Pages) Sipex Corporation – Low Noise, 300mA and 500mA CMOS LDO Regulators

Turn On Time
The turn on response is split up in two separate
response categories: the wake up time (T_WU)
and the settlling 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.
VENABLE
VOUT
t(s) = T(on)
%
2%
t(wu)
Turn Off Time
The turn off time is defined as the condition
where the output voltage drops about 66% (e) of
its total value. 5e to 7e 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 depen-
dent on load conditions, output capacitance on
V_OUT (time constant o = R_LC_L) and also on the
difference in voltage between input and output.
Thermal Considerations
The SP6203/6205 is designed to provide 300/
500 mA 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 junc-
tion-to-ambient thermal resistance of the device
and the following basic equation:
P_D = (T_J(max) - T_A) / eJ_A
THEORY OF OPERATiON: Continued
T_J(max) is the maximum junction temperature of
the die and is 125°C. T_A is the ambient tempera-
ture. e_JA is the junction-to-ambient thermal re-
sistance for the regulator and is layout depen-
dent. The SOT-23-5 package has a eJ_A of
approximately 256°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 can not
be exceeded.
Substituting P_D(max) for P_D and solving for the
operating conditions that are critical to the ap-
plication will give the maximum operating con-
ditions for the regulator circuit. For example, if
we are operating the SP6203 3.0V at room
temperature, with a minimum footprint layout
and 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 intend 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)=301.4 mW
This is well below the 523mW package maxi-
mum. Therefore, the regulator can be used.
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