Acutechnology Semiconductor Inc.

AQ112

www.acutechnology.com

8

Rev. 1.6 September 13, 2006

In applications where multiple regulated supply rails are required, it is often required that the

relationship between the various supply voltages be controlled during start-up and shutdown.

This allows for sequential, ratio-metric and simultaneous sequencing schemes.

4. Protection Diodes

Unlike older regulators, the AQ112 family does not need any protection diodes between the

adjustment pin and output or from the output to the input to prevent over-stressing the die.

Internal resistors are limiting the internal current paths on the adjustment pin. Therefore,

even with capacitors on the adjustment pin, no protection diode is needed to ensure device

safety under short circuit conditions. External diodes between the input and output are not

usually needed. Only if high value output capacitors are used (> 1000uF) and the input is

instantaneously shorted to ground, can damage occur.

5. 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 AQ112 regulators have internal thermal shutdown to protect the device from over-

heating. Under all possible operating conditions, the junction temperature of the AQ112

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 maximum allowable temperature rise,

T(max):

maximum ambient temperature which will be encountered in the application.

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

package alone will dissipate enough heat to satisfy these requirements.