APL5525 データシートの表示（PDF） - Anpec Electronics

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APL5525

Dual Channel 500mA Regulator + Reset IC

Anpec Electronics 

APL5525/5526

Application Information

Capacitor Selection and Regulator Stabil-

ity

The APL5538 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 APL5538 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 300mV transient

spike. Large output capacitor’s value and low ESR

can reduce transient spike.

Shutdown/Enable

The APL5538 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 100uA. The CONT pin cannot

be floating, a floating CONT pin may cause an inde-

terminate 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 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 APL5538. The

APL5538 is relatively immune to negative-going

glitches below the reset threshold. Typically reset delay

time is 13ms while using o.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.

Current Limit

APL5538 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=950mA. The output can be shorted

to ground for an indefinite amount of time without dam-

aging to the part.

Copyright  ANPEC Electronics Corp.

10

Rev. A.4 - Feb., 2004

www.anpec.com.tw

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