Acutechnology Semiconductor Inc.

AQ8211

www.acutechnology.com

7

Rev. 2.1 January 22, 2006

The AQ8211 develops a 1.22V reference voltage between the adjust pin terminal and

ground. This voltage is applied across the resistor R2 to generate a constant current (I2). The

current from the adjust terminal could introduce error to the output, but since it is very small

(<0.5µA) compared with the current I2 and very constant with line and load changes, the

error can be ignored. The constant current I2 then flows through resistor R1 and sets the

output voltage to the desired level.

The AQ8211 regulates the voltage that appears between its output and ground pins or

between its adjust and ground 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.

The best performance is obtained with the positive side of the resistor R1 tied near the load

and with the ground side of the resistor R2 tied near the ground of the regulator. This will

provide remote output sensing which will optimize regulation at the load.

4. Enable/Sequencing

The AQ8211 provides an enable function. The EN pin has to be at least 950 mV higher than

the output voltage for the device to be fully turned on. When the voltage of the EN pin is low

OUT

0

ENABLE

FIG.2 ENABLE 0-5V, Output follows to 3.3V out

(1V/div vertical, 200us/div horizontal)

In addition the enable function includes a sequencing feature, because when the enable pin

ramps in voltage the output voltage follows (it will be around 900 mV less than the enable

voltage until it reaches the regulation voltage) as shown in Fig. 2 above.

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.