APL5546 Ver la hoja de datos (PDF) - Anpec Electronics
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APL5546 Datasheet PDF : 17 Pages
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APL5546
Application Information
Capacitor Selection and Regulator Stabil-
ity
The APL5546 uses at least a 1uF 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 capacitors, and it’s
minimum values is recommended 4.7uF, ESR muse
be above 0.01Ω. Large output capacitor values can
reduce noise and improve load-transient response,
stability, and PSRR. Note that some ceramic dielec-
trics exhibit large capacitance and ESR variation with
Temperature. If use this capacitor, it may be neces-
sary to use 4.7uF or more to ensure stability at tem-
perature below -10°C.
Load-Transient Considerations
The APL5546 load-transient response graphs in Typi-
cal Characteristics show the transient response. A
step change in the load current from 1mA to 500mA
at 1u second will cause less than 200mV transient
spike. Large output capacitor’s value and low ESR
can reduce transient spike.
RESET
The RESET pin is asserted whenever VDET falls below
the reset threshold voltage or if CONT is forced low at
some special IC(refer timing chart and pin description).
The reset function ensures the microprocessor is prop-
erly reset and powers up into a known condition after
a power failure. RESET will remain valid with VIN as
low as 0.95V. The RESET output is a simple open-
drain N channel MOSET structure. A pull-up resistor
must be used to pull this output up to some voltage.
For most application, this voltage will be the same
power supply that supplies VIN to the APL5546. The
APL5546 is relatively immune to negative-going
glitches below the reset threshold. Typically reset delay
time is 13ms while using 0.1uF at Cd pin. If more
transient immunity is needed, a Cd capacitor can be
placed as larger as possible.
Input-Output (Dropout)Voltage
The minimun input-output voltage differential (dropout)
determines the lowest usable supply voltage. The drop-
out voltage is a function of drain-to-source on resis-
tance multiplied by the load current.
Shutdown/Enable
The APL5546 has an active high enable function. Force
CONT high (>1.6V) enables the VOUT1 , CONT low (<0.
4V) disables the VOUT1 and VOUT2 can not be affected
by CONT. Enter the shutdown mode, it also causes
the output voltage to discharge through a 500 Ω resis-
tance to ground. In shutdown mode, the quiescent
current can reduce to 70uA. The CONT pin cannot be
floating, a floating CONT pin may cause an indetermi-
nate state on the output. If it is no use, connect to VIN
for normal operation.
Current Limit
APL5546 includes two separate current-limit circuitry
for each linear regulator. The current limit protection,
which sense the current flows the P-channel MOSFET,
and controls the output voltage. The point where limit-
ing occurs is IOUT=800mA. The output can be shorted
to ground for an indefinite amount of time without dam-
aging to the part.
Copyright © ANPEC Electronics Corp.
11
Rev. A.3 - Jul., 2006
www.anpec.com.tw
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