AP1184S7 Ver la hoja de datos (PDF) - Anachip Corporation
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AP1184S7 Datasheet PDF : 11 Pages
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4A Ultra Low Dropout Positive Adjustable or Fixed-mode Regulator
Functional Descriptions(Continued)
AP1184
Vout = Vref (1+R2/R1) + Iadj * R2 where : Vref = 1.25V & Iadj=50uA Typically
Vin
Vctrl
AP1184-ADJ
Vsense
Adj
Vref
R1+
Vout
Iadj=50uA
R2+
The AP1184-ADJ keeps a constant 1.25V between
the Vsense pin and the Adj pin. By placing a
resistor R1 across these two pins and connecting
the Vsense ans Vout pin together, a constant
current flows through R1, adding to the Iadj current
and into the R2 resistor producing a voltage equal
to the (1.25/R1)*R2 + Iadj*R2. This voltage is then
added to the 1.25V to set the output voltage. This is
summarized in the above equation. Since the
minimum load current requirement of the
AP1184-ADJ is 10mA, R1 is typically selected to be
a 121Ω resistor so that it automatically satisfies
this condition. Notice that since the Iadj is typically
in the range of 50uA it only adds a small error to the
output voltage and should be considered when very
precise output voltage setting is required.
Load Regulation
Since the AP1184 has separate pins for the output
(Vout) and the sense (Vsense), it is ideal for
providing true remote sensing of the output voltage
at the load. This means that the voltage drops due
to parasitic resistance such as PCB traces between
the regulator and the load are compensated for
using remote sensing. Figure following shows a
typical application of the AP1184-ADJ with remote
sensing.
Vin
Vin
Vout
AP1184-ADJ
Vsense
Vctrl
Vctrl
Adj
R1
RL
R2
Stability
The AP1184-XXX requires the use of an output
capacitor as part of the frequency compensation in
order to make the regulator stable. Typical designs
for the microprocessor applications use standard
electrolytic capacitors with typical ESR in the range
of 50 to 100m Ω and an output capacitance of
100uF to 1000uF. Fortunately as the capacitance
increases, the ESR decreases resulting in a fixed
RC time constant. The AP1184-XXX takes
advantage of the phenomena in making the overall
regulator loop stable. For most applications a
minimum of 100uF aluminum electrolytic capacitor
insures both stability and good transient response.
Anachip Corp.
www.anachip.com.tw
Rev.1.1 Sep 7, 2004
5/11
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