LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 LP2996-N DDR Termination Regulator Check for Samples: LP2996-N FEATURES DESCRIPTION • • • • • • • • The LP2996-N linear regulator is designed to meet the JEDEC SSTL-2 specifications for termination of DDR-SDRAM. The device contains a high-speed operational amplifier to provide excellent response to load transients. The output stage prevents shoot through while delivering 1.5A continuous current and transient peaks up to 3A in the application as required for DDR-SDRAM termination. The LP2996-N also incorporates a VSENSE pin to provide superior load regulation and a VREF output as a reference for the chipset and DIMMs. 1 2 Source and Sink Current Low Output Voltage Offset No External Resistors Required Linear Topology Suspend to Ram (STR) Functionality Low External Component Count Thermal Shutdown Available in SOIC-8, SO PowerPAD-8 or WQFN-16 packages An additional feature found on the LP2996-N is an active low shutdown (SD) pin that provides Suspend To RAM (STR) functionality. When SD is pulled low the VTT output will tri-state providing a high impedance output, but, VREF will remain active. A power savings advantage can be obtained in this mode through lower quiescent current. APPLICATIONS • • • DDR-I and DDR-II Termination Voltage SSTL-2 and SSTL-3 Termination HSTL Termination Typical Application Circuit LP2996 VREF = 1.25V VREF SD SD + 0.01PF VDDQ = 2.5V VDDQ VDD = 2.5V AVIN VSENSE PVIN VTT + PF GND VTT = 1.25V + 220PF 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2002–2013, Texas Instruments Incorporated LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com 4 3 GND 2 N/C SD N/C Connection Diagram 5 1 16 N/C 6 15 VREF VDDQ 7 VSENSE 14 N/C VTT VTT 13 12 N/C 9 10 11 N/C AVIN PVIN 8 1 8 VTT SD VSENSE 2 7 PVIN 3 6 VREF 4 5 AVIN VDDQ Figure 2. SOIC-8 Layout PVIN GND GND GND 1 8 VTT SD VSENSE 2 7 PVIN 3 6 VREF 4 5 AVIN VDDQ GND Figure 1. WQFN-16 Layout (Top View) Figure 3. SO PowerPAD-8 Layout PIN DESCRIPTIONS SOIC-8 Pin or SO PowerPAD-8 Pin WQFN Pin Name 1 2 GND 2 4 SD 3 5 VSENSE 4 7 VREF Buffered internal reference voltage of VDDQ/2 5 8 VDDQ Input for internal reference equal to VDDQ/2 6 10 AVIN Analog input pin 7 11, 12 PVIN Power input pin 8 14, 15 VTT Output voltage for connection to termination resistors - 1, 3, 6, 9, 13, 16 NC No internal connection EP EP Exposed pad thermal connection. Connect to Ground. Function Ground Shutdown Feedback pin for regulating VTT. These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) AVIN to GND −0.3V to +6V PVIN to GND -0.3V to AVIN VDDQ (3) −0.3V to +6V −65°C to +150°C Storage Temp. Range Junction Temperature 150°C SOIC-8 Thermal Resistance (θJA) 151°C/W SO PowerPAD-8 Thermal Resistance (θJA) 43°C/W WQFN-16 Thermal Resistance (θJA) 51°C/W Lead Temperature (Soldering, 10 sec) 260°C ESD Rating (4) (1) (2) (3) (4) 2 1kV Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating range indicates conditions for which the device is intended to be functional, but does not ensure specific performance limits. For ensured specifications and test conditions see Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications. VDDQ voltage must be less than 2 x (AVIN - 1) or 6V, whichever is smaller. The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 Operating Range Junction Temp. Range (1) 0°C to +125°C AVIN to GND 2.2V to 5.5V PVIN Supply Voltage 0 to AVIN SD Input Voltage 0 to AVIN (1) At elevated temperatures, devices must be derated based on thermal resistance. The device in the SOIC-8 package must be derated at θJA = 151.2° C/W junction to ambient with no heat sink. Electrical Characteristics Specifications with standard typeface are for TJ = 25°C and limits in boldface type apply over the full Operating Temperature Range (TJ = 0°C to +125°C) (1). Unless otherwise specified, AVIN = PVIN = 2.5V, VDDQ = 2.5V (2). Symbol VREF Parameter VREF Voltage Conditions VIN = VDDQ = 2.3V VIN = VDDQ = 2.5V VIN = VDDQ = 2.7V Min Typ Max Units 1.135 1.235 1.335 1.158 1.258 1.358 1.185 1.285 1.385 V ZVREF VREF Output Impedance IREF = -30 to +30 μA VTT VTT Output Voltage IOUT = 0A VIN = VDDQ = 2.3V VIN = VDDQ = 2.5V VIN = VDDQ = 2.7V 1.125 1.225 1.325 1.159 1.259 1.359 1.190 1.290 1.390 IOUT = ±1.5A (3) VIN = VDDQ = 2.3V VIN = VDDQ = 2.5V VIN = VDDQ = 2.7V 1.125 1.225 1.325 1.159 1.259 1.359 1.190 1.290 1.390 -20 -25 -25 0 0 0 20 25 25 320 500 VosTT/VTT VTT Output Voltage Offset (VREF-VTT) IOUT = 0A IOUT = -1.5A (3) IOUT = +1.5A (3) IQ Quiescent Current (4) IOUT = 0A (1) ZVDDQ VDDQ Input Impedance ISD Quiescent Current in Shutdown (4) SD = 0V IQ_SD Shutdown Leakage Current SD = 0V VIH Minimum Shutdown High Level VIL Maximum Shutdown Low Level IV VTT Leakage Current in Shutdown ISENSE VSENSE Input Current TSD Thermal Shutdown TSD_HYS Thermal Shutdown Hysteresis (1) (2) (3) (4) (5) 2.5 kΩ 100 V mV µA kΩ 115 150 µA 2 5 µA 1.9 SD = 0V VTT = 1.25V See (5) V 1 0.8 V 10 µA 13 nA 165 Celcius 10 Celcius Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlation using Statistical Quality Control (SQC) methods. The limits are used to calculate Texas Instruments' Average Outgoing Quality Level (AOQL). VIN is defined as VIN = AVIN = PVIN. VTT load regulation is tested by using a 10 ms current pulse and measuring VTT. Quiescent current defined as the current flow into AVIN. The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction to ambient thermal resistance, θJA, and the ambient temperature, TA. Exceeding the maximum allowable power dissipation will cause excessive die temperature and the regulator will go into thermal shutdown. Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N 3 LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics Iq vs AVIN 1050 350 900 300 750 250 600 IQ (uA) IQ (uA) Iq vs AVIN in SD 400 200 450 150 300 100 150 50 0 2 2.5 3 3.5 4 4.5 5 5.5 2 2.5 3 3.5 4 4.5 AVIN (V) AVIN (V) Figure 4. Figure 5. VIH and VIL 5 5.5 20 30 VREF vs IREF 4 1.40 3.5 1.35 3 VREF (V) VSD (V) 1.30 2.5 2 1.25 1.20 1.5 1.15 1 0.5 2 2.5 3 3.5 4 4.5 5 1.10 -30 5.5 -20 -10 AVIN (V) IREF (uA) Figure 7. VTT vs IOUT 1.275 2.5 1.270 2 1.265 VTT (V) VREF (V) VREF vs VDDQ 1.5 1.255 0.5 1.250 0 4 1.260 1 1 2 10 Figure 6. 3 0 0 3 4 5 6 1.245 -100 -75 -50 -25 0 25 VDDQ (V) IOUT (mA) Figure 8. Figure 9. Submit Documentation Feedback 50 75 100 Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 Typical Performance Characteristics (continued) VTT vs VDDQ Iq vs AVIN in SD Temperature 400 3 350 2.5 0oC 300 IQ (uA) VTT (V) 2 1.5 125oC 250 200 1 150 0.5 100 50 0 0 1 2 3 4 5 2 6 2.5 3 3.5 4 4.5 5 5.5 AV IN (V) VDDQ (V) Figure 10. Figure 11. Iq vs AVIN Temperature Maximum Sourcing Current vs AVIN (VDDQ = 2.5V, PVIN = 1.8V) 1.4 1050 85oC 1.2 IQ (uA) 750 OUTPUT CURRENT (A) 900 25oC 600 0oC 450 300 1 0.8 0.6 0.4 0.2 150 0 0 2 2.5 3 3.5 4 4.5 5 2 5.5 2.5 AVIN (V) 3 3.5 4 4.5 5 5.5 AVIN (V) Figure 12. Figure 13. Maximum Sourcing Current vs AVIN (VDDQ = 2.5V, PVIN = 2.5V) Maximum Sourcing Current vs AVIN (VDDQ = 2.5V, PVIN = 3.3V) 1.8 3 1.7 OUTPUT CURRENT (A) OUTPUT CURRENT (A) 2.8 1.6 1.5 1.4 1.3 2.6 2.4 2.2 1.2 1.1 2 2 2.5 3 3.5 4 4.5 5 5.5 AVIN (V) 3 3.5 4 4.5 5 5.5 AVIN (V) Figure 14. Figure 15. Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N 5 LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Maximum Sourcing Current vs AVIN (VDDQ = 1.8V, PVIN = 1.8V) 3.0 1.4 2.8 1.2 2.6 1 OUTPUT CURRENT (A) OUTPUT CURRENT (A) Maximum Sinking Current vs AVIN (VDDQ = 2.5V) 2.4 2.2 2.0 1.8 0.8 0.6 0.4 0.2 1.6 0 2 2.5 3 3.5 4 4.5 5 5.5 2 2.5 3 3.5 AVIN (V) 4 4.5 5 5.5 AVIN (V) Figure 16. Figure 17. Maximum Sinking Current vs AVIN (VDDQ = 1.8V) Maximum Sourcing Current vs AVIN (VDDQ = 1.8V, PVIN = 3.3V) 2.4 3 2.2 OUTPUT CURRENT (A) OUTPUT CURRENT (A) 2.8 2 1.8 1.6 1.4 2.6 2.4 2.2 1.2 1 2 2 2.5 3 3.5 4 4.5 5 5.5 3 3.5 4 AVIN (V) 4.5 5 5.5 AVIN (V) Figure 18. Figure 19. BLOCK DIAGRAM VDDQ SD AVIN PVIN 50k VREF + - 50k + VTT VSENSE GND 6 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 Description The LP2996-N is a linear bus termination regulator designed to meet the JEDEC requirements of SSTL-2. The output, VTT is capable of sinking and sourcing current while regulating the output voltage equal to VDDQ / 2. The output stage has been designed to maintain excellent load regulation while preventing shoot through. The LP2996-N also incorporates two distinct power rails that separates the analog circuitry from the power output stage. This allows a split rail approach to be utilized to decrease internal power dissipation. It also permits the LP2996-N to provide a termination solution for the next generation of DDR-SDRAM memory (DDRII). For new designs, the LP2997 or LP2998 is recommended for DDR-II applications. The LP2996-N can also be used to provide a termination voltage for other logic schemes such as SSTL-3 or HSTL. Series Stub Termination Logic (SSTL) was created to improve signal integrity of the data transmission across the memory bus. This termination scheme is essential to prevent data error from signal reflections while transmitting at high frequencies encountered with DDR-SDRAM. The most common form of termination is Class II single parallel termination. This involves one RS series resistor from the chipset to the memory and one RT termination resistor. Typical values for RS and RT are 25 Ohms, although these can be changed to scale the current requirements from the LP2996-N. This implementation can be seen below in Figure 20. VDD VTT RT RS MEMORY CHIPSET VREF Figure 20. SSTL-Termination Scheme PIN DESCRIPTIONS AVIN AND PVIN AVIN and PVIN are the input supply pins for the LP2996-N. AVIN is used to supply all the internal control circuitry. PVIN, however, is used exclusively to provide the rail voltage for the output stage used to create VTT. These pins have the capability to work off separate supplies depending on the application. Higher voltages on PVIN will increase the maximum continuous output current because of output RDSON limitations at voltages close to VTT. The disadvantage of high values of PVIN is that the internal power loss will also increase, thermally limiting the design. For SSTL-2 applications, a good compromise would be to connect the AVIN and PVIN directly together at 2.5V. This eliminates the need for bypassing the two supply pins separately. The only limitation on input voltage selection is that PVIN must be equal to or lower than AVIN. It is recommended to connect PVIN to voltage rails equal to or less than 3.3V to prevent the thermal limit from tripping because of excessive internal power dissipation. If the junction temperature exceeds the thermal shutdown than the part will enter a shutdown state identical to the manual shutdown where VTT is tri-stated and VREF remains active. VDDQ VDDQ is the input used to create the internal reference voltage for regulating VTT. The reference voltage is generated from a resistor divider of two internal 50kΩ resistors. This ensures that VTT will track VDDQ / 2 precisely. The optimal implementation of VDDQ is as a remote sense. This can be achieved by connecting VDDQ directly to the 2.5V rail at the DIMM instead of AVIN and PVIN. This ensures that the reference voltage tracks the DDR memory rails precisely without a large voltage drop from the power lines. For SSTL-2 applications VDDQ will be a 2.5V signal, which will create a 1.25V termination voltage at VTT (See Electrical Characteristics Table for exact values of VTT over temperature). Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N 7 LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com VSENSE The purpose of the sense pin is to provide improved remote load regulation. In most motherboard applications the termination resistors will connect to VTT in a long plane. If the output voltage was regulated only at the output of the LP2996-N then the long trace will cause a significant IR drop resulting in a termination voltage lower at one end of the bus than the other. The VSENSE pin can be used to improve this performance, by connecting it to the middle of the bus. This will provide a better distribution across the entire termination bus. If remote load regulation is not used then the VSENSE pin must still be connected to VTT. Care should be taken when a long VSENSE trace is implemented in close proximity to the memory. Noise pickup in the VSENSE trace can cause problems with precise regulation of VTT. A small 0.1uF ceramic capacitor placed next to the VSENSE pin can help filter any high frequency signals and preventing errors. SHUTDOWN The LP2996-N contains an active low shutdown pin that can be used to tri-state VTT. During shutdown VTT should not be exposed to voltages that exceed AVIN. With the shutdown pin asserted low the quiescent current of the LP2996-N will drop, however, VDDQ will always maintain its constant impedance of 100kΩ for generating the internal reference. Therefore to calculate the total power loss in shutdown both currents need to be considered. For more information refer to the Thermal Dissipation section. The shutdown pin also has an internal pull-up current, therefore to turn the part on the shutdown pin can either be connected to AVIN or left open. VREF VREF provides the buffered output of the internal reference voltage VDDQ / 2. This output should be used to provide the reference voltage for the Northbridge chipset and memory. Since these inputs are typically an extremely high impedance, there should be little current drawn from VREF. For improved performance, an output bypass capacitor can be used, located close to the pin, to help with noise. A ceramic capacitor in the range of 0.1 µF to 0.01 µF is recommended. This output remains active during the shutdown state and thermal shutdown events for the suspend to RAM functionality. VTT VTT is the regulated output that is used to terminate the bus resistors. It is capable of sinking and sourcing current while regulating the output precisely to VDDQ / 2. The LP2996-N is designed to handle peak transient currents of up to ± 3A with a fast transient response. The maximum continuous current is a function of VIN and can be viewed in the Typical Performance Characteristics section. If a transient is expected to last above the maximum continuous current rating for a significant amount of time then the output capacitor should be sized large enough to prevent an excessive voltage drop. Despite the fact that the LP2996-N is designed to handle large transient output currents it is not capable of handling these for long durations, under all conditions. The reason for this is the standard packages are not able to thermally dissipate the heat as a result of the internal power loss. If large currents are required for longer durations, then care should be taken to ensure that the maximum junction temperature is not exceeded. Proper thermal derating should always be used (please refer to the Thermal Dissipation section). If the junction temperature exceeds the thermal shutdown point than VTT will tristate until the part returns below the hysteretic trip-point. 8 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 COMPONENT SELECTIONS INPUT CAPACITOR The LP2996-N does not require a capacitor for input stability, but it is recommended for improved performance during large load transients to prevent the input rail from dropping. The input capacitor should be located as close as possible to the PVIN pin. Several recommendations exist dependent on the application required. A typical value recommended for AL electrolytic capacitors is 50 µF. Ceramic capacitors can also be used, a value in the range of 10 µF with X5R or better would be an ideal choice. The input capacitance can be reduced if the LP2996-N is placed close to the bulk capacitance from the output of the 2.5V DC-DC converter. If the two supply rails (AVIN and PVIN) are separated then the 47uF capacitor should be placed as close to possible to the PVIN rail. An additional 0.1uF ceramic capacitor can be placed on the AVIN rail to prevent excessive noise from coupling into the device. OUTPUT CAPACITOR The LP2996-N has been designed to be insensitive of output capacitor size or ESR (Equivalent Series Resistance). This allows the flexibility to use any capacitor desired. The choice for output capacitor will be determined solely on the application and the requirements for load transient response of VTT. As a general recommendation the output capacitor should be sized above 100 µF with a low ESR for SSTL applications with DDR-SDRAM. The value of ESR should be determined by the maximum current spikes expected and the extent at which the output voltage is allowed to droop. Several capacitor options are available on the market and a few of these are highlighted below: AL - It should be noted that many aluminum electrolytics only specify impedance at a frequency of 120 Hz, which indicates they have poor high frequency performance. Only aluminum electrolytics that have an impedance specified at a higher frequency (between 20 kHz and 100 kHz) should be used for the LP2996-N. To improve the ESR several AL electrolytics can be combined in parallel for an overall reduction. An important note to be aware of is the extent at which the ESR will change over temperature. Aluminum electrolytic capacitors can have their ESR rapidly increase at cold temperatures. Ceramic - Ceramic capacitors typically have a low capacitance, in the range of 10 to 100 µF range, but they have excellent AC performance for bypassing noise because of very low ESR (typically less than 10 mΩ). However, some dielectric types do not have good capacitance characteristics as a function of voltage and temperature. Because of the typically low value of capacitance it is recommended to use ceramic capacitors in parallel with another capacitor such as an aluminum electrolytic. A dielectric of X5R or better is recommended for all ceramic capacitors. Hybrid - Several hybrid capacitors such as OS-CON and SP are available from several manufacturers. These offer a large capacitance while maintaining a low ESR. These are the best solution when size and performance are critical, although their cost is typically higher than any other capacitor. Thermal Dissipation Since the LP2996-N is a linear regulator any current flow from VTT will result in internal power dissipation generating heat. To prevent damaging the part from exceeding the maximum allowable junction temperature, care should be taken to derate the part dependent on the maximum expected ambient temperature and power dissipation. The maximum allowable internal temperature rise (TRmax) can be calculated given the maximum ambient temperature (TAmax) of the application and the maximum allowable junction temperature (TJmax). TRmax = TJmax − TAmax (1) From this equation, the maximum power dissipation (PDmax) of the part can be calculated: PDmax = TRmax / θJA (2) The θJA of the LP2996-N will be dependent on several variables: the package used; the thickness of copper; the number of vias and the airflow. For instance, the θJA of the SOIC-8 is 163°C/W with the package mounted to a standard 8x4 2-layer board with 1oz. copper, no airflow, and 0.5W dissipation at room temperature. This value can be reduced to 151.2°C/W by changing to a 3x4 board with 2 oz. copper that is the JEDEC standard. Figure 21 shows how the θJA varies with airflow for the two boards mentioned. Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N 9 LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com 180 170 160 150 SOP Board TJA 140 130 120 110 JEDEC Board 100 90 80 0 200 400 600 800 1000 AIRFLOW (Linear Feet per Minute) Figure 21. θJA vs Airflow (SOIC-8) Additional improvements can be made by the judicious use of vias to connect the part and dissipate heat to an internal ground plane. Using larger traces and more copper on the top side of the board can also help. With careful layout it is possible to reduce the θJA further than the nominal values shown in Figure 21 Layout is also extremely critical to maximize the output current with the WQFN package. By simply placing vias under the DAP the θJA can be lowered significantly. Figure 22 shows the WQFN thermal data when placed on a 4-layer JEDEC board with copper thickness of 0.5/1/1/0.5 oz. The number of vias, with a pitch of 1.27 mm, has been increased to the maximum of 4 where a θJA of 50.41°C/W can be obtained. Via wall thickness for this calculation is 0.036 mm for 1oz. Copper. 100 90 TJA (qC/W) 80 70 60 50 40 0 1 2 3 4 NUMBER OF VIAS Figure 22. WQFN-16 θJA vs # of Vias (4 Layer JEDEC Board)) Additional improvements in lowering the θJA can also be achieved with a constant airflow across the package. Maintaining the same conditions as above and utilizing the 2x2 via array, Figure 23 shows how the θJA varies with airflow. 10 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 51 50 qJA (oC/W) 49 48 47 46 45 0 100 200 300 400 500 600 AIRFLOW (Linear Feet Per Minute) Figure 23. θJA vs Airflow Speed (JEDEC Board with 4 Vias) Optimizing the θJA and placing the LP2996-N in a section of a board exposed to lower ambient temperature allows the part to operate with higher power dissipation. The internal power dissipation can be calculated by summing the three main sources of loss: output current at VTT, either sinking or sourcing, and quiescent current at AVIN and VDDQ. During the active state (when shutdown is not held low) the total internal power dissipation can be calculated from the following equations: PD = PAVIN + PVDDQ + PVTT where (3) PAVIN = IAVIN * VAVIN PVDDQ = VVDDQ * IVDDQ = VVDDQ2 x RVDDQ (4) (5) To calculate the maximum power dissipation at VTT both conditions at VTT need to be examined, sinking and sourcing current. Although only one equation will add into the total, VTT cannot source and sink current simultaneously. PVTT = VVTT x ILOAD (Sinking) or PVTT = ( VPVIN - VVTT) x ILOAD (Sourcing (6) (7) The power dissipation of the LP2996-N can also be calculated during the shutdown state. During this condition the output VTT will tri-state, therefore that term in the power equation will disappear as it cannot sink or source any current (leakage is negligible). The only losses during shutdown will be the reduced quiescent current at AVIN and the constant impedance that is seen at the VDDQ pin. PD = PAVIN + PVDDQ PAVIN = IAVIN x VAVIN PVDDQ = VVDDQ * IVDDQ = VVDDQ2 x RVDDQ (8) (9) (10) Typical Application Circuits Several different application circuits have been shown in Figure 24 through Figure 33 to illustrate some of the options that are possible in configuring the LP2996-N. Graphs of the individual circuit performance can be found in the Typical Performance Characteristics section in the beginning of the datasheet. These curves illustrate how the maximum output current is affected by changes in AVIN and PVIN. SSTL-2 APPLICATIONS For the majority of applications that implement the SSTL-2 termination scheme it is recommended to connect all the input rails to the 2.5V rail. This provides an optimal trade-off between power dissipation and component count and selection. An example of this circuit can be seen in Figure 24. Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N 11 LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com LP2996 VREF = 1.25V VREF SD SD + CREF VDDQ = 2.5V VDDQ VDD = 2.5V AVIN VSENSE PVIN VTT + VTT = 1.25V + GND CIN COUT Figure 24. Recommended SSTL-2 Implementation If power dissipation or efficiency is a major concern then the LP2996-N has the ability to operate on split power rails. The output stage (PVIN) can be operated on a lower rail such as 1.8V and the analog circuitry (AVIN) can be connected to a higher rail such as 2.5V, 3.3V or 5V. This allows the internal power dissipation to be lowered when sourcing current from VTT. The disadvantage of this circuit is that the maximum continuous current is reduced because of the lower rail voltage, although it is adequate for all motherboard SSTL-2 applications. Increasing the output capacitance can also help if periods of large load transients will be encountered. LP2996 VREF = 1.25V VREF SD SD + CREF VDDQ = 2.5V VDDQ AVIN = 2.2V to 5.5V AVIN VSENSE PVIN VTT PVIN = 1.8V + VTT = 1.25V + GND CIN COUT Figure 25. Lower Power Dissipation SSTL-2 Implementation The third option for SSTL-2 applications in the situation that a 1.8V rail is not available and it is not desirable to use 2.5V, is to connect the LP2996-N power rail to 3.3V. In this situation AVIN will be limited to operation on the 3.3V or 5V rail as PVIN can never exceed AVIN. This configuration has the ability to provide the maximum continuous output current at the downside of higher thermal dissipation. Care should be taken to prevent the LP2996-N from experiencing large current levels which cause the junction temperature to exceed the maximum. Because of this risk it is not recommended to supply the output stage with a voltage higher than a nominal 3.3V rail. LP2996 VREF = 1.25V VREF SD SD + VDDQ = 2.5V VDDQ AVIN = 3.3V or 5V AVIN CREF VSENSE VTT PVIN PVIN = 3.3V + CIN GND VTT = 1.25V + COUT Figure 26. SSTL-2 Implementation with higher voltage rails 12 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 DDR-II APPLICATIONS With the separate VDDQ pin and an internal resistor divider it is possible to use the LP2996-N in applications utilizing DDR-II memory. Figure 25 and Figure 26 show several implementations of recommended circuits with output curves displayed in the Typical Performance Characteristics. Figure 25 shows the recommended circuit configuration for DDR-II applications. The output stage is connected to the 1.8V rail and the AVIN pin can be connected to either a 3.3V or 5V rail. For new designs, the LP2997 or LP2998 is recommended for DDR-II applications. LP2996 VREF = 0.9V VREF SD SD + VDDQ = 1.8V VDDQ AVIN = 2.2V to 5.5V AVIN CREF VSENSE VTT PVIN PVIN = 1.8V + CIN VTT = 0.9V + GND COUT Figure 27. Recommended DDR-II Termination If it is not desirable to use the 1.8V rail it is possible to connect the output stage to a 3.3V rail. Care should be taken to not exceed the maximum junction temperature as the thermal dissipation increases with lower VTT output voltages. For this reason it is not recommended to power PVIN off a rail higher than the nominal 3.3V. The advantage of this configuration is that it has the ability to source and sink a higher maximum continuous current. LP2996 + CREF VDDQ = 1.8V VDDQ AVIN = 3.3V or 5.5V AVIN VSENSE PVIN VTT PVIN = 3.3V + CIN VREF= 0.9V VREF SD SD GND VTT = 0.9V + COUT Figure 28. DDR-II Termination with higher voltage rails LEVEL SHIFTING If standards other than SSTL-2 are required, such as SSTL-3, it may be necessary to use a different scaling factor than 0.5 times VDDQ for regulating the output voltage. Several options are available to scale the output to any voltage required. One method is to level shift the output by using feedback resistors from VTT to the VSENSE pin. This has been illustrated in Figure 29 and Figure 30. Figure 29 shows how to use two resistors to level shift VTT above the internal reference voltage of VDDQ/2. To calculate the exact voltage at VTT the following equation can be used. VTT = VDDQ/2 ( 1 + R1/R2) (11) Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N 13 LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com LP2996 VDDQ VDDQ VDD AVIN VTT VTT R1 PVIN + VSENSE COUT + GND CIN R2 Figure 29. Increasing VTT by Level Shifting Conversely, the R2 resistor can be placed between VSENSE and VDDQ to shift the VTT output lower than the internal reference voltage of VDDQ/2. The equations relating VTT and the resistors can be seen below: VTT = VDDQ/2 (1 - R1/R2) (12) LP2996 VDDQ VDDQ VDD AVIN R2 VSENSE R1 VTT PVIN VTT + + COUT GND CIN Figure 30. Decreasing VTT by Level Shifting HSTL APPLICATIONS The LP2996-N can be easily adapted for HSTL applications by connecting VDDQ to the 1.5V rail. This will produce a VTT and VREF voltage of approximately 0.75V for the termination resistors. AVIN and PVIN should be connected to a 2.5V rail for optimal performance. LP2996 VDDQ = 1.5V VDDQ VDD = 2.5V AVIN + CREF VSENSE VTT PVIN + CIN VREF = 0.75V VREF SD SD GND VTT = 0.75V + COUT Figure 31. HSTL Application QDR APPLICATIONS Quad data rate (QDR) applications utilize multiple channels for improved memory performance. However, this increase in bus lines has the effect of increasing the current levels required for termination. The recommended approach in terminating multiple channels is to use a dedicated LP2996-N for each channel. This simplifies layout and reduces the internal power dissipation for each regulator. Separate VREF signals can be used for each DIMM bank from the corresponding regulator with the chipset reference provided by a local resistor divider or one of the LP2996-N signals. Because VREF and VTT are expected to track and the part to part variations are minor, there should be little difference between the reference signals of each LP2996-N. 14 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N LP2996-N www.ti.com SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 OUTPUT CAPACITOR SELECTION For applications utilizing the LP2996-N to terminate SSTL-2 I/O signals the typical application circuit shown in Figure 30 can be implemented. LP2996 VREF = 1.25V VREF SD SD + VDDQ = 2.5V VDDQ VDD = 2.5V AVIN 0.01PF VSENSE VTT PVIN + VTT = 1.25V + GND PF 220PF Figure 32. 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 advisable to use multiple bulk capacitors and addition to high frequency decoupling. Figure 31 shown below 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 used for their low ESR and low cost. LP2996 SD VREF = 1.25V VREF SD + VDDQ = 2.5V VDDQ VDD = 2.5V AVIN 0.01PF VSENSE PVIN + 47PF VTT GND VTT = 1.25V + + 330PF 330PF Figure 33. 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. Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N 15 LP2996-N SNOSA40J – NOVEMBER 2002 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision I (March 2013) to Revision J • 16 Page Changed layout of National Data Sheet to TI format .......................................................................................................... 15 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LP2996-N PACKAGE OPTION ADDENDUM www.ti.com 11-Apr-2013 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish (2) MSL Peak Temp Op Temp (°C) Top-Side Markings (3) (4) LP2996LQ ACTIVE WQFN NHP 16 1000 TBD Call TI Call TI 0 to 125 L00006B LP2996LQ/NOPB ACTIVE WQFN NHP 16 1000 Green (RoHS & no Sb/Br) SN Level-3-260C-168 HR 0 to 125 L00006B LP2996LQX ACTIVE WQFN NHP 16 4500 TBD Call TI Call TI 0 to 125 L00006B LP2996LQX/NOPB ACTIVE WQFN NHP 16 4500 Green (RoHS & no Sb/Br) SN Level-3-260C-168 HR 0 to 125 L00006B LP2996M ACTIVE SOIC D 8 95 TBD Call TI Call TI 0 to 125 2996M LP2996M/NOPB ACTIVE SOIC D 8 95 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM 0 to 125 2996M LP2996MR ACTIVE SO PowerPAD DDA 8 95 TBD Call TI Call TI 0 to 125 LP2996 LP2996MR/NOPB ACTIVE SO PowerPAD DDA 8 95 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR 0 to 125 LP2996 LP2996MRX ACTIVE SO PowerPAD DDA 8 2500 TBD Call TI Call TI 0 to 125 LP2996 LP2996MRX/NOPB ACTIVE SO PowerPAD DDA 8 2500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR 0 to 125 LP2996 D 8 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM 0 to 125 2996M LP2996MX/NOPB ACTIVE SOIC (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 11-Apr-2013 Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) Multiple Top-Side Markings will be inside parentheses. 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Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 26-Mar-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LP2996LQ WQFN NHP 16 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 LP2996LQ/NOPB WQFN NHP 16 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 LP2996LQX WQFN NHP 16 4500 330.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 LP2996LQX/NOPB WQFN NHP 16 4500 330.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 LP2996MRX SO Power PAD DDA 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LP2996MRX/NOPB SO Power PAD DDA 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LP2996MX/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 26-Mar-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LP2996LQ WQFN NHP 16 1000 210.0 185.0 35.0 LP2996LQ/NOPB WQFN NHP 16 1000 213.0 191.0 55.0 LP2996LQX WQFN NHP 16 4500 367.0 367.0 35.0 LP2996LQX/NOPB WQFN NHP 16 4500 367.0 367.0 35.0 LP2996MRX SO PowerPAD DDA 8 2500 367.0 367.0 35.0 LP2996MRX/NOPB SO PowerPAD DDA 8 2500 367.0 367.0 35.0 LP2996MX/NOPB SOIC D 8 2500 367.0 367.0 35.0 Pack Materials-Page 2 MECHANICAL DATA DDA0008A MRA08A (Rev D) www.ti.com MECHANICAL DATA NHP0016A LQA16A (REV A) www.ti.com IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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