Electronic Components Datasheet Search |
|
MAX8504ETC Datasheet(PDF) 11 Page - Maxim Integrated Products |
|
MAX8504ETC Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 14 page PWM Buck Converters with Bypass FET for N-CDMA/W-CDMA Handsets ______________________________________________________________________________________ 11 Input Capacitor Selection Capacitor ESR is a major contributor to input ripple in high-frequency DC-to-DC converters. Ordinary aluminum electrolytic capacitors have high ESR and should be avoided. Low-ESR tantalum capacitors or polymer capacitors are better and provide a compact solution for space-constrained surface-mount designs. Ceramic capacitors have the lowest ESR overall. The input filter capacitor reduces peak currents and noise at the input voltage source. Connect a low-ESR bulk capacitor ( ≥10µF typ) to the input. Select this bulk capacitor to meet the input ripple requirements and voltage rating rather than capacitance value. Use the following equation to calculate the maximum RMS input current: Compensation, Stability, and Output Capacitor The MAX8500–MAX8504 are externally compensated by placing a resistor and a capacitor (see Figures 1 and 2, RC and CC) in series from COMP to GND. An additional capacitor (Cf) may be required from COMP to GND if high-ESR output capacitors are used. The capacitor integrates the current from the transconduc- tance amplifier, averaging output capacitor ripple. This sets the device speed for transient response and allows the use of small ceramic output capacitors because the phase-shifted capacitor ripple does not disturb the current-regulation loop. The resistor sets the proportional gain of the output error voltage by a factor gm ✕ RC. Increasing this resistor also increases the sensitivity of the control loop to output ripple. The resistor and capacitor set a compensation zero that defines the system’s transient response. The load cre- ates a dynamic pole, shifting in frequency with changes in load. As the load decreases, the pole frequency shifts to the left. System stability requires that the compensa- tion zero must be placed to ensure adequate phase margin (at least 30° at unity gain). See Figures 1 and 2 for RC and CC recommended values. Inductor Selection A 4µH to 6µH inductor is recommended for most appli- cations. For best efficiency, the inductor’s DC resis- tance should be <400m Ω. Saturation current (ISAT) should be greater than the maximum DC load at the PA’s supply plus half the inductor current ripple. Two- step VCC applications typically require very small inductors with ISAT in the 200mA to 300mA region. See Table 1 and Table 2 for recommended inductors and manufacturers. PC Board Layout and Routing High switching frequencies and large peak currents make PC board layout a very important part of design. Good design minimizes EMI, noise on the feedback paths, and voltage gradients in the ground plane, all of which can result in instability or regulation errors. Connect the inductor, input filter capacitor, and output filter capacitor as close together as possible and keep their traces short, direct, and wide. Connect their ground pins at a single common node in a star ground configuration. The external voltage-feedback network should be very close to the FB pin, within 0.2in (5mm). Keep noisy traces, such as those from the LX pin, away from the voltage-feedback network. Position the bypass capacitors as close as possible to their respective pins to minimize noise coupling. For optimum performance, place input and output capacitors as close to the device as possible. Connect GND and PGND directly under the IC to the exposed paddle. The MAX8504 evaluation kit manual illustrates an example PC board layout and routing scheme. Chip Information TRANSISTOR COUNT: 2530 PROCESS: BiCMOS I I V VV V RMS OUT IN OUT IN OUT =× × () - |
Similar Part No. - MAX8504ETC |
|
Similar Description - MAX8504ETC |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |