Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
ACT4921QI Datasheet(PDF) 26 Page - Active-Semi, Inc |
|
ACT4921QI Datasheet(HTML) 26 Page - Active-Semi, Inc |
26 / 35 page ACT4921QI Rev 1.0, 18-Jan-2018 Innovative PowerTM www.active-semi.com ActiveSwitcherTM is a trademark of Active-Semi Copyright © 2018 Active-Semi, Inc. 26 Inductor Selection The Buck regulator utilizes current-mode control and a proprietary internal compensation scheme to simultaneously simplify external component selection and optimize transient performance over their full operating range. The ACT4921 is optimized for operation with 1uH to 3.3uH inductors. Choose an inductor with a low DC-resistance, and avoid inductor saturation by choosing inductors with DC ratings that exceed the maximum output current by at least 30%. Due to the requirement for the buck converter to start up as quickly as possible, the inductor should be designed to give a maximum ripple current, ΔIL, of 50% to 60% of the maximum output current. The following equation calculates the recommended inductor value. ∗ ∗∆ Equation 7 Where L is the inductor value in µH, VBUCK is the output voltage, VSTR is the maximum storage voltage, FSW is the switching frequency in Hz, and ΔIL is the desired ripple current in Amperes. Output Capacitor Selection The buck converter is designed to take advantage of the benefits of ceramic capacitors, namely small size and very-low ESR. The buck converter is designed to operate with 44µF output capacitor over most of its operating ranges, although more capacitance may be desired depending on the duty cycle and load step requirements. Choose a ripple voltage that is approximately 1% of the output voltage setpoint. Note that the output capacitance must be placed at the output of the buck converter. Additional downstream capacitance will be placed at the loads, but this capacitance should not be considered when calculating the buck output capacitance. However, the downstream capacitance should be considered when compensating the power supply. The following equation calculates the output voltage ripple as a function of output capacitance. Note that the worst case ripple voltage occurs at the beginning of supplement mode when the storage capacitors are fully charged. COUT ∆ ∗ ∗ Equation 8 Where Vripple is the desired output ripple voltage, FSW is the switching frequency in Hz, and ΔIL is the maximum ripple current in Amperes. As with the input capacitor selection, use X5R or X7R dielectrics and be sure to consider the capacitor’s DC bias effects. Storage Boost Converter General Description The ACT4921 contains an integrated peak current- mode, synchronous boost converter. It minimizes system level costs by using the same components as the buck converter. The peak current is adjustable between 250mA and 950mA, allowing for system optimization. The output voltage is adjustable between 5V and 28V via I2C registers and an external resistor. The peak current-mode control topology eliminates the need for compensation. The boost automatically charges up the storage capacitors from the input voltage so they are ready to provide backup power in the event of a system fault. Startup The boost converter automatically starts when the IC exits the SOFTSTART state and the ENB pin is pulled high. Note that the IC exits the SOFTSTART state 10ms after the output voltage is within 200mV of the input voltage. Most systems wait until the system is up and running before enabling the buck and boost with the ENB pin. When the storage voltage reaches regulation, the boost enters standby mode and monitors the storage voltage. It automatically turns back on and “tops off” the storage capacitors when the storage voltage drops below 95% of the programmed voltage. The boost converter automatically turns off if it is “topping off” the storage capacitors when the IC enters supplement mode. The average input current when the boost charges the storage capacitors is approximately ½ of the peak switching current. The peak switch current is programed by register BST_CLIM[1:0]. Table 6: Boost Peak Current Settings BST_CLIM[1:0] (mA) 00 250 01 500 10 950 11 1500 |
Número de pieza similar - ACT4921QI |
|
Descripción similar - ACT4921QI |
|
|
Enlace URL |
Política de Privacidad |
ALLDATASHEET.ES |
¿ALLDATASHEET es útil para Ud.? [ DONATE ] |
Todo acerca de Alldatasheet | Publicidad | Contáctenos | Política de Privacidad | Intercambio de Enlaces | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |