AQ111 Datasheet, PDF (7/9 Pages) Acutechnology Semiconductor – Low Dropout 1 Amp Voltage Regulator

Acutechnology Semiconductor Inc.
AQ111
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.
To determine if a heatsink is needed, the power dissipated by the regulator, P_D, must be
calculated:
P_D= (V_IN-V_OUT) I_L
where the I_L is the load current.
The next parameter which must be calculated is the maximum allowable temperature rise,
T(max):
T(max)=T_J(max)-T_A(max)
where T_J(max) is the maximum allowable junction temperature (125°C), and T_A(max) is the
maximum ambient temperature which will be encountered in the application.
Using the calculated values for T(max) and P_D, the maximum allowable value for the
junction to ambient thermal resistance (θ_JA) can be calculated:
θ_JA=T(max)/ P_D
If the maximum allowable value for θ_JA is found to be greater than the junction to ambient
thermal resistance for the package used, no heatsink is needed since the package alone will
dissipate enough heat to satisfy these requirements.
Package Dimensions
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Rev. 1.5 September 13, 2006