0

Date: Apr2-07

SP6203/SP6205 Low Noise, 300 and 500mA CMOS LDO Regulators

© 2007 Sipex Corporation

0

Date: 2//05

SP6203/6205 Low Noise, 300 and 500mA CMOS LDO Regulators

© Copyright 2005 Sipex Corporation

THEORY OF OPERATiON: Continued

Turn On Time

The turn on response is split up in two separate

defined as the time it takes for the output to rise

to 2% of its total value after being released from

definedastheconditionwheretheoutputreaches

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.

sistance for the regulator and is layout depen-

approximately 256°C/W for minimum PCB

copper footprint area.

This results in a maximum power dissipation of:

The actual power dissipation of the regulator

circuit can be determined using one simple

equation:

To prevent the device from entering thermal

shutdown. maximum power dissipation can not

be exceeded.

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).

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:

This is well below the 523mW package maxi-

mum. Therefore, the regulator can be used.

Turn Off Time

The turn off time is defined as the condition

where the output voltage drops about 66% ( ) of

its total value. 5 to 7 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

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:

2%

t(s) = T(on)

%

t(wu)

VOUT

VENABLE