Acutechnology Semiconductor Inc.

AQ533

www.acutechnology.com

8

Rev. 1.7 September 13, 2006

The AQ533 provides Reverse Current Protection. When the AQ533 is turned off, no

current will flow from the output to input. A small current will flow from output to ground

through the Vout set resistors R1 and R2. The need for protection diodes is eliminated.

6. Thermal Considerations

When an integrated circuit operates with an appreciable current, its junction temperature is

elevated. It is important to quantify its thermal limits in order to achieve acceptable

performance and reliability. This limit is determined by summing the individual parts

consisting of a series of temperature rises from the semiconductor junction to the operating

environment. The heat generated at the device junction flows through the die to the die

attach pad, through the lead frame to the surrounding case material, to the printed circuit

board, and eventually to the ambient environment.

The AQ533 regulators have internal thermal shutdown to protect the device from over-

heating. Under all possible operating conditions, the junction temperature of the AQ533

must be lower than 125°C. A heatsink may be required depending on the maximum power

dissipation and maximum ambient temperature of the application.

calculated:

The next parameter, which must be calculated, is the max. allowable temperature rise, T(max):

maximum ambient temperature, which will be encountered in the application.

thermal resistance for the package used, no heatsink is needed since the package alone will

dissipate enough heat to satisfy these requirements.

7. Ultra low Dropout Operation

This feature is important when the supply voltage is dropping near the output regulated voltage.

Furthermore if the voltage dropout is low, the internal power dissipation is also reduced and the

thermal requirements of the device are less stringent.