Electronic Components Datasheet Search |
|
LP2998MRX Datasheet(PDF) 16 Page - Texas Instruments |
|
LP2998MRX Datasheet(HTML) 16 Page - Texas Instruments |
16 / 26 page VTT LP2998 PVIN VDDQ VREF AVIN VREF = 1.25V VSENSE GND 47 PF + + + VDDQ = 2.5V VDD = 2.5V VTT = 1.25V 330 PF SD SD + 330 PF 0.01 PF VTT LP2998 PVIN VDDQ VREF AVIN VSENSE GND + + + SD SD CIN COUT CREF AVIN = 2.5V VDDQ = 1.8V VTT = 0.9V VREF = 0.9V LP2998 SNVS521I – DECEMBER 2007 – REVISED APRIL 2013 www.ti.com OUTPUT CAPACITOR SELECTION For applications utilizing the LP2998 to terminate SSTL-2 I/O signals the typical application circuit shown in Figure 27 can be implemented. Figure 27. Typical SSTL-2 Application Circuit This circuit permits termination in a minimum amount of board space and component count. Capacitor selection can be varied depending on the number of lines terminated and the maximum load transient. However, with motherboards and other applications where VTT is distributed across a long plane, it is recommended to use multiple bulk capacitors in addition to high frequency decoupling. Figure 28 depicts an example circuit where 2 bulk output capacitors could be situated at both ends of the VTT plane for optimal placement. Large aluminum electrolytic capacitors are typically used for their low ESR and low cost. Figure 28. Typical SSTL-2 Application Circuit for Motherboards In most PC applications, an extensive amount of decoupling is required because of the long interconnects encountered with the DDR-SDRAM DIMMs mounted on modules. As a result, bulk aluminum electrolytic capacitors in the range of 1000uF are typically used. PCB Layout Considerations 1. The input capacitor for the power rail should be placed as close as possible to the PVIN pin. 2. VSENSE should be connected to the VTT termination bus at the point where regulation is required. For motherboard applications an ideal location would be at the center of the termination bus. 3. VDDQ can be connected remotely to the VDDQ rail input at either the DIMM or the Chipset. This provides the most accurate point for creating the reference voltage. 4. For improved thermal performance excessive top side copper should be used to dissipate heat from the package. Numerous vias from the ground connection to the internal ground plane will help. Additionally these can be located underneath the package if manufacturing standards permit. 5. Care should be taken when routing the VSENSE trace to avoid noise pickup from switching I/O signals. A 0.1uF ceramic capacitor located close to the SENSE can also be used to filter any unwanted high frequency signal. This can be an issue especially if long SENSE traces are used. 6. VREF should be bypassed with a 0.01 µF or 0.1 µF ceramic capacitor for improved performance. This capacitor should be located as close as possible to the VREF pin. 16 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LP2998 |
Similar Part No. - LP2998MRX |
|
Similar Description - LP2998MRX |
|
|
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 |