AQ8211 Datasheet, PDF (7/10 Pages) Acutechnology Semiconductor – Ultra-Low Dropout 500mA Voltage Regulator with Enable

Acutechnology Semiconductor Inc.
AQ8211
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
the device is in shutdown mode and it will not draw any current from the VIN terminal.
ENABLE
OUT
0
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.
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Rev. 2.1 January 22, 2006