APL1581
Typical Characteristics
Control Pin Current vs. Output Current
V
IN-
V
OUT
=1.0V
80
70
Control Pin Current vs. Output Current
V
IN-
V
OUT
=4.25V
70
T
J
=-50°C
T
J
=0°C
T
J
=25°C
T
J
=75°C
VCNTL Pin Current (mA)
60
50
40
30
20
VCNTL Pin Current (mA)
60
50
40
T
J
=-50°C
T
J
=0°C
T
J
=25°C
T
J
=75°C
30
20
10
0
T
J
=125°C
10
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
T
J
=125°C
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Output Current (A)
Output Current (A)
Application Information
General
The APL1581 (adjustable or fixed) regulator is a 5 ter-
minal device designed specifically to provide extremely
low dropout voltages comparable to the PNP type with-
out 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 regu-
lator that provides 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 applications where dual inputs are
available, such as a computer motherboard with an
ATX power supply that provides 5V and 3.3V to the
board.
APL1581 is equipped with a 1.25V reference, preci-
sion and fast voltage regulations, on-chip current and
thermal limits, and remote sensing capability to re-
duce system total cost.
Copyright
©
ANPEC Electronics Corp.
Rev. B.5 - Mar., 2008
8
APL1581 is available in SOP-8P, TO-252-5,
TO-263-5, and TO-220-5 packages to meet different
power dissipation applications.
Output Voltage Setting
See Figure 1 Adjustable APL1581 develops a 1.25V
reference voltage between the VSENSE pin and the
ADJ pin. Placing a resistor between these two termi-
nals 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 speci-
fied minimum load current of 10mA.The current out of
the ADJ pin is small, typically 50µA and itadds to the
current from R1. Because IADJ is very small, it needs
to be considered only when very precise output volt-
age setting is required. For best regulation, the top of
the resistor divider should be connected directly to
the SENSE pin. The adjustable APL1581 can be pro-
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