Acutechnology Semiconductor Inc.

AQ111

www.acutechnology.com

6

Rev. 1.5 September 13, 2006

Application Notes

1. Typical Application

Notes:

1. Output voltage is 1.22V * (R2 +R1)/R1

2. Input and output capacitors should be located close to the device.

3. The AQ111 will remain stable with C1 and C2 as low as 1.0µF. Overall transient

performance is improved with increased capacitance.

2. Stability

An input capacitor is recommended. A 1.0µF capacitor on the input is a suitable input

bypassing for almost all applications. A larger capacitor is also suitable. In the adjustable

improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the

less than R1 (being R1 the resistor between the output and the adjust pin) to prevent the

ripple from being amplified:

R1 is normally in the range of 1KΩ.

The output capacitor is critical in maintaining regular stability. The AQ111 is stable with an

output capacitor greater than. Of course any increase of the output capacitor will merely improve

the loop stability and the load transient response. In the case of the adjustable regulator, when

best stability over a wide range of loads and are recommended.

3. Output Voltage

The AQ111 adjustable version develops a 1.22V reference voltage between the output and

the adjust pin terminal. This voltage is applied across the resistor R1 to generate a constant

current (I1). The current from the adjust terminal could introduce error to the output, but since

it is very small (< 20µA) compared with the current I1 and very constant with line and load

changes, the error can be ignored. The constant current I1 then flows through resistor R2

and sets the output voltage to the desired level.

For fixed voltages the resistor R1 and R2 are integrated inside the devices.