Acutechnology Semiconductor Inc.
AQ533
Application Notes
1. Typical Application
Notes:
1. Output voltage is 1.22V * (R1 +R2)/R2
2. Input and output capacitors should be located close to the device.
3. The AQ533 will remain stable with C1 and C3 as low as 0.1
µF
and 1.0
µF
respectively.
Overall transient performance is improved with increased capacitance and the addition of C2.
4. The output is fully enabled when Enable is 950 mV above the expected V
OUT
. EN may
be driven by either a digital or analog signal to control either turn-on time or to give full
control of risetime.
5. Enable, tied to any separate source >0.95V + V
OUT
, will insure Ultra-low drop out voltage
(350mV@ 500mA) from V
IN
to V
OUT
. Or, Enable, tied to Vin will support a low drop out
voltage (0.95V).
2. Stability
An
Enable
capacitor is recommended. A 100nF capacitor is a suitable input bypass for
almost all applications. A larger capacitor is also suitable depending on the cleanliness of the
Enable source.
A
Vin
Capacitor is also recommended. A 1µF capacitor is a bypassing for almost all applications.
A larger capacitor is also suitable depending on the cleanliness of the V
IN
source.
The
Output
capacitor is critical in maintaining regular stability. The AQ533 is stable with an
output capacitor greater than 1µF. Any increase of the output capacitor will merely improve
the loop stability and the load transient response.
Tantalum Capacitors exhibit the best stability over a wide range of loads and are recommended.
3. Output Voltage
The AQ533 meets all specifications down to 1.22V output. It does not suffer from
performance degradation issues such as experienced with CMOS LDO’s. Drop out voltage
will be less than
350 mV at 500 mA
load with the
ENABLE
pin held greater than 0.95V + Vout,
The AQ533 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
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Rev. 1.7
September 13, 2006
ACUTECH [ ACUTECHNOLOGY SEMICONDUCTOR ]
