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APL5546-AKAC-TRL Datasheet(PDF) 11 Page - Anpec Electronics Coropration |
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APL5546-AKAC-TRL Datasheet(HTML) 11 Page - Anpec Electronics Coropration |
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11 / 17 page  Copyright © ANPEC Electronics Corp. Rev. A.3 - Jul., 2006 www.anpec.com.tw 11 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 0.01 Ω. 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. 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. 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. 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. |
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