APL1581 View Datasheet(PDF) - Anpec Electronics
Part Name
Description
MFG CO.
'APL1581' PDF : 17 Pages View PDF
APL1581
Application Information (Cont.)
Output Voltage Setting (Cont.)
grammable to any voltages in the range of 1.25V to 5.5V
according to the following formula:
R2
VOUT = VREF x (1+ R1 ) + IADJ x R2
where VREF = 1.25V (typical)
IADJ = 50µA (typical)
The recommended R1 is in range of 100Ω to125Ω to
satisfy the minimum load current requirement. Proper
sizes of R2 and R1 are also concerned for power
dissipation.
VIN
VCNT L
VIN
VOU T
APL1581
VCNTL VSENSE
AD J
VRE F
R1
VOUT
IA DJ=50uA
R2
Figure 1 Setting Output Voltage
Grounding and Output Sensing
The APL1581 allows true Kelvin sensing for both the
high and low side of the load. Figure 2 shows the de-
vice connected to take advantage of the remote sense
feature. The SENSE pin and the top of the resistor
divider are connected to the top of the load; the bot-
tom of the resistor divider is connected to the bottom
of the load. Typically the load is a microprocessor
and parasitic resistance RP is made up of the PC traces
and /or connector resistance between the regulator
and the processor. RP is now connectedinside the
regulation loop of the APL1581 and for reasonable val-
ues of RP the load regulation at the load will be
negligible. Voltage drops due to RP are not eliminated;
they will add to the dropout voltage of the regulator
regardless of whether they are inside or outside the
regulation loop.
VIN
VCNTL
VIN
VOU T
APL1581
VCN TL VSENSE
AD J
R1
VOUT
Load
Adjustable
R2
Device
VIN
VCNTL
VIN
VOU T
APL1581
VCN TL VSENSE
GN D
RP
VOUT
Load
Fixed Voltage
Device
RP
Figure 2 Remote Voltage Sensing
Stability and Output Capacitors
The circuit design of using the APL1581 series re-
quires an output capacitor as part of the device fre-
quency compensation. The following chart shows a
stable region to select output capacitor for APL1581.
This region above the curve indicates minimum re-
quired ESR and capacitance to maintain stability.
However, the output capacitor should have an ESR
less than1Ω.
100
80
60
40
20
0
1
Stable Region
10
100
Capacitance(µF)
1000
Copyright © ANPEC Electronics Corp.
9
Rev. B.5 - Mar., 2008
www.anpec.com.tw
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