APL5312_09 Datasheet, PDF (8/15 Pages) Anpec Electronics Coropration – Ultra-Low-Noise, High PSRR, Low-Dropout, 300mA Linear Regulator

APL5312
Application Information
Output Voltage Selection
The APL5312 are supplied with factory-set output volt-
ages from 1.5V to 3.5V.
Capacitor Selection and Regulation Stability
The APL5312 uses at least a 1µF capacitor on the input.
This capacitor can use Aluminum, Tantalum, or Ceramic
capacitors. Input capacitor with large value and low ESR
provides better PSRR and line-transient response. The
output capacitor also can use Aluminum, Tantalum, or
Ceramic capacitor, and its proper values is at least 1µF,
ESR must be above 25mΩ. Large output capacitor val-
ues can reduce noise and improve load-transient
response, stability, and PSRR. With X5R and Y5V
dielectrics, 1µF is sufficient at all operating temperatures.
The selection of output capacitor’s is important because
it with C_OUT form a zero to provide the sufficient phase
margin (see the Figure C ESR vs. Load Current).
OUT
Bypass Capacitor
Use a 10nF bypass capacitor at BP for low-output voltage
noise. The leakage current going into the BP pin should
be less than 10nA. Increasing the capacitance slightly
decreases the output noise. Value above 0.1µF and be-
low 1nF are not recommended (see the Figure Output
Noise vs. BP Capacitance).
Noise, PSRR, and Load-Transient Response
The APL5312 is designed to deliver ultra-low noise and
high PSRR, as well as low dropout and low quiescent
currents in battery–powered systems. When operating
from sources other than batteries, improve PSRR and
transient response can be achieved by increasing input
and output capacitors, and bypass capacitor to form the
passive filtering techniques (see Output Noise vs. BP
Capacitance).
Shutdown
The APL5312 has an active high enable function. Force
SHDN high (>1.6V) enables the V , SHDN low (<0.4V) dis-
OUT
ables the V . Enter the shutdown mode, it also causes
OUT
the output voltage to discharge through a 500Ω resis-
tance to ground. In shutdown mode, the quiescent cur-
rent can reduce to 0.1µA. The SHDN pin cannot be floating,
a floating SHDN pin may cause an indeterminate state
on the output. If it is no use, connect to V_IN for normal
operation.
Input-Output (Dropout) Voltage
The minimum input-output voltage differential (dropout)
determines the lowest usable supply voltage. The drop-
out voltage is a function of drain-to-source on resistance
multiplied by the load current.
Current Limit
APL5312 includes a current-limit circuitry for linear
regulator. The current-limit protection, which senses the
current flowing to the P-channel MOSFET, and controls
the output voltage. The point where limiting occurs is
I =500mA. The output can be shortened to the ground
OUT
for an indefinite amount of time without damaging to the
part.
Thermal Protection
Thermal protection limits total power dissipation in the
APL5312. When the junction temperature exceeds
+160°C, the thermal sensor generates a logic signal to
turn off the pass element and let IC to cool. When the IC’s
junction temperature cools down by 20°C, the thermal
sensor will turn the pass element on again, resulting in a
pulsed output during continuous thermal protection. Ther-
mal protection is designed to protect the IC in the event of
fault conditions.
Operating Region and Power Dissipation
The thermal resistance of the case and circuit board,
ambient and junction air temperature, and the rate of air
flow all control the APL5312’s maximum power
dissipation. The power dissipation across the device is
P = I_OUT (V_IN-V_OUT). The maximum power dissipation is:
P
MAX
=
(T
J
-
T)
A
/
(θ_JC
+
θ_CA )
θ_JA = θ_JC + θ_CA
where T_J - T_A is the temperature difference between the
junction and ambient air.
θ_JC is the thermal resistance of the package, θ_CA is the
thermal resistance through the printed circuit board, cop-
per traces, and other materials to the surrounding air, θ_JA
Copyright © ANPEC Electronics Corp.
8
Rev. A.4 - Jun., 2009
www.anpec.com.tw