AQ1541 Datasheet, PDF (8/10 Pages) Acutechnology Semiconductor – Low Dropout 1 Amp Voltage Regulator with Enable Function

Acutechnology Semiconductor Inc.
AQ1541
shutdown. To this end, the AQ1541 allows for an analog control of the output voltage via the
ENBL pin. This allows for sequential, ratio-metric and simultaneous sequencing schemes.
In a simple sequencing scheme, the output voltage can be delayed with respect to the
application of Vin by connecting an RC network as shown in figure 3 below. This RC
generates a slow ramp at the enable pin; the output follows 800 mV below this ramp until the
output reaches regulation.
Virtually no current flows into the enable pin until it reaches the enable voltage which is
equal to Vout + 800 mV. Therefore, the time delay can be reliably set by using the time
constant of a known RC to slow the of the enable pin.
FIG.3 Enable delay circuit
The Enable and Output raise with respect to a Vin is shown in Fig.3 below. Vin = 5V, Vout =
2.5V, RC = 100 KΩ and 100 nF. The output is in regulating 13 ms after the input supply is
applied.
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FIG. 4 Enable circuit delays output
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Rev. 2.2 September 13, 2005