Acutechnology Semiconductor Inc.
AQ1541
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.
The AQ1541 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. Enable/Sequencing
The AQ1541 provides an enable function. The EN pin has to be at least 800 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 800 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
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