APL5551 Ver la hoja de datos (PDF) - Anpec Electronics
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APL5551 Datasheet PDF : 17 Pages
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APL5551
Application Information
Capacitor Selection and Regulator Stability
The APL5551 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 capacitors, and it’s minimum
values is recommended 4.7µF, 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 dielectrics exhibit large
capacitance and ESR variation with Temperature. If use
this capacitor, it may be necessary to use 4.7µF or
more to ensure stability at temperature below -10°C.
Load-Transient Considerations
The APL5551 load-transient response graphs in Typical
Characteristics show the transient response. A step
change in the load current from 1mA to 500mA at 1µ
second will cause less than 200mV transient spike.
Large output capacitor’s value and low ESR can reduce
transient spike.
Shutdown/Enable
The APL5551 has an active high enable function. Force
CONT high (>1.6V) enables the VOUT1, CONT low
(<0.4V) disables the V and V can not be affected
OUT1
OUT2
by CONT. In shutdown mode, the quiescent current
can reduce to 70µA. The CONT pin cannot be floating,
a floating CONT pin may cause an indeterminate state
on the output. If it is no use, connect to VIN for normal
operation.
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
properly 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 APL5551. The
APL5551is relatively immune to negative-going glitches
below the reset threshold. Typically reset delay time
is 13ms while using 0.1µF 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
dropout voltage is a function of drain-to-source on
resistance multiplied by the load current.
Current Limit
APL5551 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
limiting occurs is IOUT=800mA. The output can be
shorted to ground for an indefinite amount of time
without damaging to the part.
Thermal Protection
Thermal protection limits total power dissipation in the
APL5551. When the junction temperature exceeds
TJ=+170°C, the thermal sensor generate a logic signal
to turn off the pass transistor and let IC to cool. When
the IC’s junction temperature cools by 15°C, the
thermal sensor will turn the pass transistor on again,
resulting in a pulsed output during continuous thermal
protection. Thermal protection is designed to protect
the IC in the event of fault conditions. For continual
Copyright © ANPEC Electronics Corp.
11
Rev. A.2 - Oct., 2005
www.anpec.com.tw
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