Acutechnology Semiconductor Inc.

AQ111

www.acutechnology.com

7

Rev. 1.5 September 13, 2006

The AQ111 regulates the voltage that appears between its output and ground pins or

between its output and adjust pins. In some cases, line resistances can introduce errors to

the voltage across the load. To obtain the best load regulation a few precautions are needed.

For example it is important to minimize the line resistances to the load, so the load itself

should be tied directly to the output terminal on the positive side and directly to the ground

terminal on the negative side.

When the adjustable regulator is used, the best performance is obtained with the positive

side of the resistor R1 tied directly to the output terminal of the regulator rather than near the

load. This will eliminate line drops from appearing effectively in series with the reference and

degrading regulation. In addition the ground side of the resistor R2 can be returned near the

ground of the load to provide remote ground sensing and improve load regulation. A

capacitor (470pF) between the ADJ pin and system ground will enhance stability.

4. Protection Diodes

Unlike older regulators, the AQ111 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 AQ111 regulators have internal thermal shutdown to protect the device from over-

heating. Under all possible operating conditions, the junction temperature of the AQ111

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.

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

dissipate enough heat to satisfy these requirements.

Package Dimensions