APL1581-15KA Anpec Electronics Corporation, APL1581-15KA Datasheet - Page 9

• Manufacturer Part Number: APL1581-15KA
• Description: Dual Input Low Dropout Regulator
• Manufacturer: Anpec Electronics Corporation

APL1581
General
The APL1581 (adjustable or fixed) regulator is a 5 termi-
nal device designed specifically to provide extremely low
dropout voltages comparable to the PNP type without the
disadvantage of the extra power dissipation due to the
base current associated with PNP regulators. This is done
by bringing out the control pin of the regulator that pro-
vides the base current to the power NPN and connecting
it to a voltage that is greater than the voltage present at
the VIN pin. This flexibility makes APL1581 ideal for appli-
cations where dual inputs are available, such as a com-
puter motherboard with an ATX power supply that pro-
vides 5V and 3.3V to the board.
APL1581 is equipped with a 1.25V reference, precision
and fast voltage regulations, on-chip current and thermal
limits, and remote sensing capability to reduce system
total cost.
APL1581 is available in SOP-8P, TO-252-5, and TO-263-
5 packages to meet different power dissipation
applications.
Output Voltage Setting
See Figure 1 Adjustable APL1581 develops a 1.25V ref-
erence voltage between the VSENSE pin and the ADJ pin.
Placing a resistor between these two terminals causes a
constant current to flow through R1 and down through R2
to set the overall output voltage. In general, R1 is chosen
so that this current is the specified minimum load current
of 10mA. The current out of the ADJ pin is small, typically
50 A and itadds to the current from R1. Because IADJ is
very small, it needs to be considered only when very pre-
cise output voltage setting is required. For best regulation,
the top of the resistor divider should be connected di-
rectly to the SENSE pin. The adjustable APL1581 can be
programmable to any voltages in the range of 1.25V to
5.5V according to the following formula:
where
Application Information
Copyright
Rev. B.6 - Feb., 2009
V
V
I
ADJ
OUT
REF
= 50 A (typical)
= 1.25V (typical)
= V
ANPEC Electronics Corp.
REF
x (1+
R2
R1
) + I
ADJ
x R2
9
V
The recommended R1 is in range of 100
satisfy the minimum load current requirement. Proper
sizes of R2 and R1 are also concerned for power
dissipation.
Grounding and Output Sensing
The APL1581 allows true Kelvin sensing for both the high
and low side of the load. Figure 2 shows the device con-
nected 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 bottom 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 resis-
tance between the regulator and the processor. RP is
now connectedinside the regulation loop of the APL1581
and for reasonable values 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 regu-
lator regardless of whether they are inside or outside the
regulation loop.
V
V
CNTL
CNTL
V
IN
IN
Figure 1. Setting Output Voltage
VIN
VCNTL
Adjustable
VCNTL
VIN
Device
APL1581
ADJ
APL1581
VSENSE
VOUT
ADJ
VSENSE
I
ADJ
VOUT
=50 A
R1
R2
V
www.anpec.com.tw
REF
RP
R2
R1
to125
V
OUT
Load
V
OUT
to