LM2614 NSC | Alldatasheet
Document overview
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Technical content
Features
n Sub-miniature 10-bump thin micro SMD package n Uses small ceramic capacitors n 5mV typ PWM mode output voltage ripple(C OUT = 22µF) n Internal soft start n Current overload protection n Thermal Shutdown n External compensation
Applications
n Battery Powered RF Devices August 2002 LM2614 400mA Sub-Miniature Adjustable DC-DC Converter Optimized for RF Power Amplifiers © 2002 National Semiconductor Corporation DS200367 www.national.com
Ordering Information
Order Number Package Type NSC Package Marking (*) Supplied As LM2614ATL 10-bump Wafer Level Chip Scale (micro SMD) XYTT S50A 250 Tape and Reel LM2614BTL XYTT S50B 250 Tape and Reel LM2614ATLX XYTT S50A 3000 Tape and Reel LM2614BTLX XYTT S50B 3000 Tape and Reel (*) XY - denotes the date code marking (2 digit) in production (*) TT - refers to die run/lot traceability for production (*) S - product line designator Package markings may change over the course of production. Pin Description Pin Number Pin Name Function A1 FB Feedback Analog Input. B1 EANEG Inverting input of error amplifier C1 EAOUT Output of error amplifier D1 SYNC/MODE Synchronization Input. Use this digital input for frequency selection or modulation control. Set: SYNC/MODE = high for low-noise 600kHz PWM mode SYNC/MODE = low for low-current PFM mode SYNC/MODE = a 500kHz–1MHz external clock for synchronization in PWM mode. (See Synchronization and Operating Modesin the Device Informationsection.) D2 EN Enable Input. Set this Schmitt trigger digital input high for normal operation. For shutdown, set low. Set EN low during system power-up and other low supply voltage conditions. (See Shutdown Modein the Device Informationsection.) D3 PGND Power Ground C3 SW Switching Node connection to the internal PFET switch and NFET synchronous rectifier. Connect to an inductor with a saturation current rating that exceeds the max Switch Peak Current Limit of the LM2614. B3 PVIN Power Supply Voltage Input to the internal PFET switch. Connect to the input filter capacitor. A3 VDD Analog Supply Input. If board layout is not optimum, an optional 0.1µF ceramic capacitor is suggested. A2 SGND Analog and Control Ground LM2614 www.national.com3
Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. PVIN, VDD to SGND −0.2V to +6V PGND to SGND, PVIN to VDD −0.2V to +0.2V EN, EAOUT, EANEG, SYNC/MODE to SGND −0.2V to +6V FB, SW (GND −0.2V) to (VDD +0.2V) Storage Temperature Range −45˚C to +150˚C Lead Temperature (Soldering, 10 sec.) 260˚C Junction Temperature (Note 2) −25˚C to +125˚C Minimum ESD Rating ±2k V (Human Body Model, C = 100 pF, R = 1.5 k Ω) Thermal Resistance (θJA) (Note 3) 140˚C/W
Electrical Characteristics
Specifications with standard typeface are for T A =T J = 25˚C, and those in boldface type apply over the full Operating Tem- perature Range of TA =T J = −25˚C to +85˚C. Unless otherwise specified, PVIN = VDD = EN = SYNC/MODE = 3.6V. Symbol Parameter Conditions Min Typ Max Units VIN Input Voltage Range PVIN = VDD = V IN (Note 4) 2.8 3.6 5.5 V VFB Feedback Voltage 1.485 1.50 1.515 V VHYST PFM Comparator Hysteresis Voltage PFM Mode (SYNC/MODE = 0V) (Note 5) 24 mV ISHDN Shutdown Supply Current VIN = 3.6V, EN = 0V 0.02 3 µA IQ1_PWM DC Bias Current into VDD SYNC/MODE = VIN F B=2 V 600 725 µA IQ2_PFM SYNC/MODE = 0V F B=2 V 160 195 µA RDSON (P) Pin-Pin Resistance for P FET 395 550 m Ω RDSON (N) Pin-Pin Resistance for N FET 330 500 m Ω RDSON (TC) FET Resistance Temperature Coefficient 0.5 %/C ILIM Switch Peak Current Limit (Note 6) LM2614ATL 510 690 850 mALM2614BTL 400 690 980 VIH Logic High Input, EN, SYNC/MODE 0.95 1.3 V VIL Logic Low Input, EN, SYNC/MODE 0.4 0.80 V FSYNC SYNC/MODE Clock Frequency Range (Note 7) 500 1000 kHz FOSC Internal Oscillator Frequency LM2614ATL, PWM Mode 468 600 732 kHzLM2614BTL, PWM Mode 450 600 750 Tmin Minimum ON-Time of PFET Switch in PWM Mode 200 ns Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but device specifications may not be guaranteed. For guaranteed specifications and associated test conditions, see the Min and Max limits and Conditions in the Electrical Characteristics table. Typical (typ) specifications are mean or average values at 25˚C and are not guaranteed. Note 2: Thermal shutdown will occur if the junction temperature exceeds 150˚C. Note 3: Thermal resistance specified with 2 layer PCB (0.5/0.5 oz. cu). Note 4: The LM2614 is designed for mobile phone applications where turn-on after system power-up is controlled by the system controller. Thus, it should be ke pt in shutdown by holding the EN pin low until the input voltage exceeds 2.8V. Note 5: The hysteresis voltage is the minimum voltage swing on the FB pin that causes the internal feedback and control circuitry to turn the internal PFET swit ch on and then off during PFM mode. When resistor dividers are used like in the operating circuit of Figure 4, the hysteresis at the output will be the value of the Note 6: Current limit is built-in, fixed, and not adjustable. If the current limit is reached while the voltage at the FB pin is pulled below 0.7V, the internal PFET switch turns off for 2.5µs to allow the inductor current to diminish. Note 7: SYNC driven with an external clock switching between V IN and GND. When an external clock is present at SYNC; the IC is forced to be in PWM mode at the external clock frequency. The LM2614 synchronizes to the rising edge of the external clock. LM2614 www.national.com 4
Typical Performance Characteristics LM2614ATL, Circuit of Figure 4,V IN = 3.6V, T A = 25˚C, unless otherwise noted. Quiescent Supply Current vs Supply Voltage Shutdown Quiescent Current vs Temperature (Circuit in Figure 3) 20036708 20036722 Output Voltage vs Supply Voltage (VOUT = 1.0V, PWM MODE) Output Voltage vs Supply Voltage (VOUT = 1.5V, PWM MODE) 20036724 20036709 Output Voltage vs Output Current (VOUT = 1.0V, PWM MODE) Output Voltage vs Output Current (VOUT = 1.5V, PWM MODE) 20036710 20036711 LM2614 www.national.com5
Typical Performance Characteristics LM2614ATL, Circuit of Figure 4,V IN = 3.6V, T A = 25˚C, unless otherwise noted. (Continued) Output Voltage vs Output Current (VOUT = 3.6V, PWM MODE) Dropout Voltage vs Output Current (VOUT = 3.6V, PWM MODE) 20036732 20036712 Switching Frequency vs Temperature (Circuit in Figure 3, PWM MODE) Feedback Bias Current vs Temperature (Circuit in Figure 3) 20036723 20036731 Efficiency vs Output Current (VOUT = 1.0V, PWM MODE) Efficiency vs Output Current (VOUT = 1.0V, PWM MODE, with Diode) 20036713 20036714 LM2614 www.national.com 6
Typical Performance Characteristics LM2614ATL, Circuit of Figure 4,V IN = 3.6V, T A = 25˚C, unless otherwise noted. (Continued) Efficiency vs Output Current (VOUT = 1.5V, PWM MODE) Efficiency vs Output Current (VOUT = 1.5V, PWM MODE, with Diode) 20036715 20036716 Efficiency vs Output Current (VOUT = 3.6V, PWM MODE) Efficiency vs Output Current (VOUT = 3.6V, PWM MODE, with Diode) 20036717 20036718 LM2614 www.national.com7
Typical Performance Characteristics LM2614ATL, Circuit of Figure 4,V IN = 3.6V, T A = 25˚C, unless otherwise noted. (Continued) Efficiency vs Output Voltage (PWM MODE, with Diode) 20036730 Device Information The LM2614 is a simple, step-down DC-DC converter opti- mized for powering RF power amplifiers (PAs) in mobile phones, portable communicators, and similar battery pow- ered RF devices. It is designed to allow the RF PA to operate at maximum efficiency over a wide range of power levels from a single LiION battery cell. It is based on a current-mode buck architecture, with synchronous rectifica- tion in PWM mode for high efficiency. It is designed for a maximum load capability of 400mA (300mA for B grade) in PWM mode. Maximum load range may vary from this de- pending on input voltage, output voltage and the inductor chosen. The device has all three of the pin-selectable operating modes required for powering RF PAs in mobile phones and other sophisticated portable devices with complex power management needs. Fixed-frequency PWM operation offers full output current capability at high efficiency while minimiz- ing interference with sensitive IF and data acquisition cir- cuits. During standby operation, hysteretic PFM mode re- duces quiescent current to 160µA typ. to maximize battery life. Shutdown mode turns the device off and reduces battery consumption to 0.02µA (typ). DC PWM mode feedback voltage precision is ±1%. Effi- ciency is typically 96% for a 200mA load with 3.6V output, 3.9V input. The efficiency can be further increased by using a schottky diode like MBRM120 as shown in Figure 4. PWM mode quiescent current is 600µA typ. The output voltage is dynamically programmable from 1.0V to 3.6V by adjusting the voltage on the VCON at the external feedback resistors. This ensures longer battery life by being able to change the PA supply voltage dynamically depending on its transmitting power. Additional features include soft-start, current overload pro- tection, over voltage protection and thermal shutdown pro- tection. The LM2614 is constructed using a chip-scale 10-pin thin micro SMD package. This package offers the smallest pos- sible size, for space-critical applications such as cell phones, where board area is an important design consideration. Use of a high switching frequency (600kHz) reduces the size of external components. Board area required for implementa- tion is only 0.58in 2 (375mm2). Use of a micro-SMD package requires special design con- siderations for implementation. (See Micro SMD Package Assembly and Usein the Application Informationsection.) Its fine bump-pitch requires careful board design and precision assembly equipment. LM2614 www.national.com 8
Device Information (Continued) extending battery life when the load is in a low-power standby mode. In PFM mode, quiescent current into the VDD pin is 160µA typ. In contrast, PWM mode VDD-pin quiescent current is 600µA typ. PWM operation is intended for use with loads of 50mA or more, when low noise operation is desired. Below 100mA, PFM operation can be used to allow precise regulation, and reduced current consumption. However, it should be noted that for PA applications the PFM mode need not be used as output voltage slew rates are of more concern to the system designer. The LM2614 has an over-voltage feature that pre- vents the output voltage from rising too high, when the device is left in PWM mode under low-load conditions. See Overvoltage Protection, for more information. Switch modes with the SYNC/MODE pin, using a signal with a slew rate faster than 5V/100µs. Use a comparator, Schmitt trigger or logic gate to drive the SYNC/MODE pin. Do not leave the pin floating or allow it to linger between thresholds. These measures will prevent output voltage errors in re- sponse to an indeterminate logic state. The LM2614 switches on each rising edge of SYNC. Ensure a minimum load to keep the output voltage in regulation when switching modes frequently. FREQUENCY SYNCHRONIZATION The SYNC/MODE input can also be used for frequency synchronization. During synchronization, the LM2614 ini- tiates cycles on the rising edge of the clock. When synchro- nized to an external clock, it operates in PWM mode. The device can synchronize to a 50% duty-cycle clock over frequencies from 500kHz to 1MHz. If a different duty cycle is used other than 50% the range for acceptable duty cycles are 30% to 70%. Use the following waveform and duty cycle guidelines when applying an external clock to the SYNC/MODE pin. Clock under/overshoot should be less than 100mV below GND or above V DD. When applying noisy clock signals, especially sharp edged signals from a long cable during evaluation, terminate the cable at its characteristic impedance and add an RC filter to the SYNC pin, if necessary, to soften the slew rate and over/undershoot. Note that sharp edged signals from a pulse or function generator can develop under/overshoot as high as 10V at the end of an improperly terminated cable. OVERVOLTAGE PROTECTION The LM2614 has an over-voltage comparator that prevents the output voltage from rising too high when the device is left in PWM mode under low-load conditions. When the output voltage rises by about 100mV ( Figure 3) over its regulation threshold, the OVP comparator inhibits PWM operation to skip pulses until the output voltage returns to the regulation threshold. When resistor dividers are used the OVP thresh- old at the output will be the value of the threshold at the feedback pin times the resistor divider ratio. In over voltage protection, output voltage and ripple will increase. SHUTDOWN MODE Setting the EN digital input pin low ( <0.4V) places the LM2614 in a 0.02µA (typ) shutdown mode. During shutdown, the PFET switch, NFET synchronous rectifier, reference, control and bias circuitry of the LM2614 are turned off. Setting EN high enables normal operation. While turning on, soft start is activated. EN should be set low to turn off the LM2614 during system power-up and undervoltage conditions when the supply is less than the 2.8V minimum operating voltage. The LM2614 is designed for compact portable applications, such as mo- bile phones. In such applications, the system controller de- termines power supply sequencing. Although the LM2614 is typically well behaved at low input voltages, this is not guar- anteed. INTERNAL SYNCHRONOUS RECTIFICATION While in PWM mode, the LM2614 uses an internal NFET as a synchronous rectifier to reduce rectifier forward voltage drop and associated power loss. Synchronous rectification provides a significant improvement in efficiency whenever the output voltage is relatively low compared to the voltage drop across an ordinary rectifier diode. The internal NFET synchronous rectifier is turned on during the inductor current down slope during the second part of each cycle. The synchronous rectifier is turned off prior to the next cycle, or when the inductor current ramps to zero at light loads. The NFET is designed to conduct through its intrinsic body diode during transient intervals before it turns on, elimi- nating the need for an external diode. CURRENT LIMITING A current limit feature allows the LM2614 to protect itself and external components during overload conditions. In PWM mode cycle-by-cycle current limit is normally used. If an excessive load pulls the voltage at the feedback pin down to approximately 0.7V, then the device switches to a timed current limit mode. In timed current limit mode the internal P-FET switch is turned off after the current comparator trips and the beginning of the next cycle is inhibited for 2.5µs to force the instantaneous inductor current to ramp down to a safe value. Timed current limit mode prevents the loss of current control seen in some products when the voltage at the feedback pin is pulled low in serious overload conditions. DYNAMICALLY ADJUSTABLE OUTPUT VOLTAGE The LM2614 can be used to provide dynamically adjustable output voltage by using external feedback resistors. The output can be varied from 1.0V to 3.6V in less than 30µs by using an analog control signal (VCON) at the external feed- back resistors. This feature is useful in PA applications where peak power is needed only when the handset is far away from the base station or when data is being transmit- ted. In other instances the transmitting power can be re- duced and hence the supply voltage to the PA can be reduced helping maintain longer battery life. See Setting the Output Voltage in the Application Information section for further details. In dropout conditions the output voltage is V IN −I OUT (Rdc + RDSON (P)) where Rdc is the series resistance of the inductor and RDSON (P) is the on resistance of the PFET. LM2614 www.national.com11
Application Information
SETTING THE OUTPUT VOLTAGE The LM2614 can be used with external feedback resistors and an analog signal to vary the output voltage. Select an output voltage from 1.0V to 3.6V by setting the voltage on the VCON as directed in Table 1. TABLE 1. Output Voltage Selection
- Select the value of R2 to allow at least 100 times the
feedback pin bias current to flow through it. create a pole on the order of 10Hz or less. resistance should be less than 0.3 Ω for good efficiency. Table 2lists suggested inductors and suppliers. TABLE 2. Suggested Inductors and Their Suppliers
and COUT. Use of tantalum capacitors is not recommended. 3 lists suggested capacitors and suppliers. transient load changes and reduces output voltage ripple. tance and sufficiently low ESR to perform these functions. value is at least 4.7µF for the application circuit in Figure 1. tors is a major factor in voltage ripple. TABLE 3. Suggested Capacitors and Their Suppliers facilitate placement of the device. for specific instructions how to do this. special attention must be paid to the pads for bumps D3–B3. or inadequate reflow of these bumps. sible size in applications with red or infrared opaque cases. lation characteristic of larger devices, it is vulnerable to light. EMI, ground bounce, and resistive voltage loss in the traces. solder joints can result in erratic or degraded performance. ing a few simple design rules.
- Place the LM2614, inductor and filter capacitors close
Application Information (Continued) 3. Arrange the components so that the switching current loops curl in the same direction.During the first half of each cycle, current flows from the input filter capacitor, through the LM2614 and inductor to the output filter capacitor and back through ground, forming a current loop. In the second half of each cycle, current is pulled up from ground, through the LM2614 by the inductor, to the output filter capacitor and then back through ground, forming a second current loop. Routing these loops so the current curls in the same direction prevents mag- netic field reversal between the two half-cycles and re- duces radiated noise. 4. Connect the ground pins of the LM2614, and filter ca- pacitors together using generous component-side cop- per fill as a pseudo-ground plane. Then, connect this to the ground-plane (if one is used) with several vias.This reduces ground-plane noise by preventing the switching currents from circulating through the ground plane. It also reduces ground bounce at the LM2614 by giving it a low-impedance ground connection. 5. Use wide traces between the power components and for power connections to the DC-DC converter circuit.This reduces voltage errors caused by resistive losses across the traces. 6. Route noise sensitive traces, such as the voltage feed- back path, away from noisy traces between the power components. The voltage feedback trace must remain close to the LM2614 circuit and should be routed directly from V OUT at the output capacitor and should be routed opposite to noise components. This reduces EMI radi- ated onto the DC-DC converter’s own voltage feedback trace. 7. Place noise sensitive circuitry, such as radio IF blocks, away from the DC-DC converter, CMOS digital blocks and other noisy circuitry. Interference with noise-sensitive circuitry in the system can be reduced through distance. In mobile phones, for example, a common practice is to place the DC-DC converter on one corner of the board, arrange the CMOS digital circuitry around it (since this also generates noise), and then place sensitive preamplifiers and IF stages on the diagonally opposing corner. Often, the sensitive circuitry is shielded with a metal pan and power to it is post-regulated to reduce conducted noise, using low-dropout linear regulators. LM2614 www.national.com15
Physical Dimensions inches (millimeters) unless otherwise noted NOTES: UNLESS OTHERWISE SPECIFIED 1. EPOXY COATING 2. 63Sn/37Pb EUTECTIC BUMP 3. RECOMMEND NON-SOLDER MASK DEFINED LANDING PAD. 4. PIN A1 IS ESTABLISHED BY LOWER LEFT CORNER WITH RESPECT TO TEXT ORIENTATION. 5. XXX IN DRAWING NUMBER REPRESENTS PACKAGE SIZE VARIATION WHERE X1 IS PACKAGE WIDTH, X2 IS PACKAGE LENGTH AND X3 IS PACKAGE HEIGHT. 6. REFERENCE JEDEC REGISTRATION MO-211. VARIATION BD. 10-Bump micro SMD Package The dimensions for X1, X2 and X3 are as given: X1 = 2.250 ±0.030 mm X2 = 2.504 ±0.030 mm X3 = 0.600 ±0.075 mm LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Corporation Americas Email: support@nsc.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507 www.national.com LM2614 400mA Sub-Miniature Adjustable DC-DC Converter Optimized for RF Power Amplifiers National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the righ t at any time without notice to change said circuitry and specifications.