APL5331
Application Information
General
The APL5331 is a linear regulator and is capable of
sourcing or sinking current up to 3A. The APL5331
has fast transient response, accurate output voltage
(small voltage offset, load regulation), active-low shut-
down control and fault protections (current-limit, ther-
mal shutdown). The APL5331 is available in several
packages to meet different of power dissipation in
requirement various applications.
Output Voltage Regulation
The output voltage at VOUT pin tracks the reference
voltage applied at VREF pin. Two internal NPN pass
transistors controlled by separate high bandwidth er-
ror amplifiers regulate the output voltage by sourcing
current from VIN pin or sinking current to GND pin.
The base currents of the pass transistors are pro-
vided by VCNTL pin. An internal kelvin sensing
scheme use at the VOUT pin for perfect load regula-
tion at various load current. To prevent the two pass
transistors from shoot-through, a small voltage offset
is created between the positive inputs of the two error
amplifiers. This results in higher output voltage while
the regulator sinks light or heavy load current. Since
the APL5331 exhibits very fast load transient
response, lesser amount of capacitors can be use.
In addition, capacitors with high ESR can also be
use.
Current Limit
The APL5331 monitors sourcing and sinking current,
and limits the maximum output current to prevent dam-
ages during overload or short-circuit, To increase
the input voltage of VIN or VCNTL will get higher
current-limit points.
Shutdown and Soft-Start
The VREF pin is a dual-function input pin, acting as
reference input and shutdown control input. Apply-
ing and holding a voltage below 0.35V(typ.) to VREF
pin shuts down the output of the regulator. An NPN
transistor or N-channel MOSFET is used to pull down
the VREF while applying a “high” signal to turn on the
transistor. When shutdown function is active, the
two pass transistors are turned off and the imped-
ance of the VOUT is about 10MΩ (typ.), sourcing or
sinking no current. When release the VREF pin, the
current through the resistor divider charges the soft-
start capacitor to initiate a soft-start cycle. The output
voltage tracks the rising VREF. The soft start process
limits the input surge current.
Thermal Shutdown
An thermal shutdown circuit limits the junction tem-
perature of the APL5331. When the junction tem-
perature exceeds T
J
= +150
o
C, a thermal sensor turns
off both pass transistors, allowing the device to cool
down. The regulator starts to regulate again after the
junction temperature reduces by 40
o
C, resulting in a
pulsed output during continuous thermal overload
conditions. The thermal limit designed with a 40
o
C
hysteresis lowers the average T
J
during continuous
thermal overload conditions, extend life time of
APL5331.
Copyright
ANPEC Electronics Corp.
Rev. A.8 - Oct., 2003
10
www.anpec.com.tw
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
