Innovations Embedded CMOS LDO Regulators for portable devices White Paper ROHM MarketingUSA Presented by ROHM Semiconductor CMOS LDO Regulators for Portable Devices Introduction Power management has become an increasingly LDOs provide a power management solution satisfying important design consideration for numerous products, the need for low power, space-conscious design and especially those relying on battery power. Complicating low switching-noise voltage regulation while adhering to the power management situation, as more features get the cost constraints of these applications. integrated into products, the number of required voltage Other LDO applications include PC motherboards, supplies increases. With a common 3.6-V lithium-ion graphic cards, post-regulation in switching power sup- battery, a highly integrated product such as a smart plies, telecom equipment and consumer applications phone can require ten or more different voltages for: such as HDTVs. In addition, automotive applications 1. Global positioning system (GPS) continue to use LDOs for their low switching noise and 2. Power amplifier low cost. 3. Memory According to Susie Inouye, Research Director and 4. Baseband and DSP core Principal Analyst at market research firm Databeans, 5. Applications (picture, music and video) processing “LDOs are still the best fit for low current applications. 6. Low voltage wireless LAN complex switching regulators. Noise performance in 7. Display back light LED drivers portable electronics is an important design consider- They are inexpensive and have lower noise than more ation, particularly in wireless as high frequency parts can 8. Display CCD impact performance of sensitive analog RF circuits. As 9. Audio long as price, size, and noise performance matter, there 10. Photo flash charger will be a growing market for LDOs.” To handle all of these voltages, cell phones typically Databeans forecasts a compound average growth rate have power management ICs with multiple LDOs. (CAGR) of 15% unit growth for LDOs from 2009 to However, depending on the location of the load, an 2014. Advances in the latest CMOS LDOs are among individual LDO may be used. the reasons for this growth. While switching regulators garner a lot of attention This paper reviews the basics of LDO regulators and because of their high efficiency, low drop-out (LDO) discusses the technology advances in the latest genera- linear voltage regulators offer the optimum answer for tion of LDOs that make them the preferred solution for powering circuitry in many of the portable device appli- many point of load power requirements. The paper will cations. The latest generation of LDOs is optimized for also introduce ROHM Semiconductor’s extensive line of cell phones, PDAs, MP3 players, notebooks, cameras, CMOS LDO regulators and discuss their unique benefits camcorders and other handheld portable systems. in portable electronics applications. ROHM Semiconductor LDO Regulators 1 Pass Element Q1 VIN VOUT Error Amplification VREF _ OUT Bandgap Reference R1 + VC R2 Figure 1. The pass element, Q1, in a low drop out regulator operates in the linear range and can be a bipolar NPN or PNP transistor, a Darlington pair, or an N-channel or P-channel MOSFET. The Basic LDO Topology operating current. (For example, ROHM’s recently intro- Low drop-out linear regulators are designed to operate with minimal voltage differences between the source voltage (VIN ) and the regulated output voltage (VOUT ). This value, known as the saturation voltage (VSAT ) is duced PB1 series requires just 20 μA under high-speed operation and only 2 μA when in its unique power-save mode.) The resulting LDO design provides optimized performance for portable applications. typically in the 100 mV to 200 mV range. This allows for effective regulation of load voltages as battery voltage Comparison of LDOs to PWM Regulators diminishes as the battery discharges. For the majority of applications within portable devices The basic LDO topology is shown in Figure 1. Using where loads are operated from a battery source, the a resistor divider, a voltage-controlled current source LDO offers a simple, small and cost-effective solution. determines the output voltage. Key elements include While it is true that switching regulators are more effi- the voltage reference, an error amplifier and the series cient than LDOs, there are several other factors that pass transistor. Input and output capacitors are typi- must be considered in selecting the right device for the cally among the few external components required for job. proper LDO operation. Pulse-width modulated (PWM) switching regulators typ- Advanced LDOs utilize BiCMOS process technology ically operate between 50 kHz to 1 MHz and produce to provide higher efficiency, additional application- electromagnetic interference (EMI) that can disrupt both specific features and space-saving packaging. With analog and RF circuits. In contrast, the switching in BiCMOS, a merged bipolar and CMOS wafer fabrica- LDOs occurs in the bandgap reference and the level is tion process, an LDO designer can take advantage in the microvolt, rms range over a defined bandwidth, a of circuit elements of each technology. For example, level that is considerably lower than a switching regula- the bandgap reference is an ideal bipolar circuit ele- tor. This is a major design advantage in noise-sensitive ment while the output pass transistor can be a highly applications. efficient P-channel MOSFET that results in very low ROHM Semiconductor LDO Regulators 2 Additional advantages of fewer external components, Regulator Type Linear (LDO) Switching simple design process, small footprint, and lower cost External Components advantage --- make LDOs a preferred solution for regulated power Noise sensitivity advantage --- Design Complexity simple complex Cost advantage --- lower than the source voltage. Moreover, the latest Footprint advantage --- advances in CMOS LDOs, such as BiCMOS devices Step-down (buck voltage) yes yes Step-up (boost voltage) no yes Efficiency --- advantage Thermal design --- advantage in many applications where the controlled voltage is with a P-channel output transistor and power down capabilities as found in ROHM CMOS LDO regulators, significantly reduce the efficiency advantage of PWM Table 1. Compared to switching regulators, LDOs have several design areas where their advantages make them a compelling choice. regulators – particularly in low-current applications. Table 1 summarizes the significant points of compari- to consider the level of electrostatic discharge (ESD) son between LDO and switching regulators. withstand capability. Finally, package size must be taken into consideration in selecting the right device for Selecting the Right LDO for the Job space-conscious portable devices. An LDO’s drop out voltage, the type and range of input Figure 2 illustrates several features that can be added voltage, required output voltage, maximum load current to an LDO to satisfy application requirements in the lat- and power dissipation (Pd) are key factors in product est portable and wireless products. This paper will dis- selection. In portable applications, it is also important cuss the importance of many of these features. High ripple rejection Stable Operation Reduced input/output voltage difference VIN VREF VOUT STBY 0μA standby current COUT TSD APS OCP Temperature protection High output precision Overcurrent protection Automatic Power Saving Ceramic capacitor compatibility Discharge circuit for secure startup Figure 2. Additional circuitry and advanced packaging can make an LDO the ideal choice for a particular application. ROHM CMOS LDO regulators are available in several series offering many of these advanced features. ROHM Semiconductor LDO Regulators 3 Package Size and Power Dissipation Automatic Power Saving Function Packaging has a significant impact on PCB space and With CMOS processing, advanced features such as power dissipation. For example, an HVSOF5 (1.6 x 1.6 an Automatic Power Saving (APS) function can be 2 mm ) packaged LDO is over 70% smaller than a 2.8 x designed to further increase the efficiency of an LDO. 2.9-mm2 SOT23-5, achieving the same current rating With APS, the circuit varies the current consumption while improving the effective power dissipation (Pd). based on the value of the load. This can result in as much as 90% less current during no load conditions. ROHM ROHM ROHM ROHM VCSP60N1 SSON004X1216 HVSOF5 HVSOF6 1.0 1.2 1.04 1.6 1.2 1.6 1.6 1.6 1.6 1.6 1.6 1.6 3.0 3.0 0.6 540 mW 220 mW 410 mW 680 mW 87% smaller 76% smaller 70% smaller 40% smaller 76% smaller 54% smaller 39% smaller NA 2.8 Conventional SOT23-5 2.9 540 mW 2.1 Conventional SC82 2.0 400 mW Figure 3. A small LDO package provides a substantial space savings for portable applications and with the right substrate design, can dissipate 100s of milliwatts. Figure 3 shows the size reduction of four ROHM LDO High-Speed Load Response packages and nominal power disipation compared to the industry-standard SOT23-5 (ROHM SSOP5) and CMOS LDOs are ideal for powering microcontrollers, digital signal processors, microprocessors, memory SC82 packages. and other digital logic circuits. A critical feature in this In many packages, an integrated heatsink increases the application is high-speed load response. If the regulator heat transfer allowing the package to safely dissipate does not respond quickly enough, its output has the more heat. The ability to dissipate more heat is espe- potential to fall below the minimum voltage differential cially useful in high-density portable devices. The safe required for reliable operation. A low VSAT allows stable power dissipation for a particular package also depends on the ambient temperature and mounting substrate. operation even when the battery is close to being fully discharged. Package ratings (e.g. SSOP5: 540 mW; HVSOF6: 680 mW; HVSOF5: 410 mW; SSON004X1216: 220 mW; and VCSP60N1: 540 mW; VSON008X2030: 660 mW) are for power dissipation at 25°C operation. The value of Pd normally decreases with increasing ambient temperature. In addition, the power dissipation will differ depending on the mounting conditions and substrate (board type, size and copper foil area). ROHM Semiconductor Figure 4 demonstrates the importance of fast load response. A “conventional” LDO exhibits nearly 100 mV drop in VOUT, compared to the ROHM BUxxTA2 Series LDO optimized for high-speed load response. This added margin can reduce the potential for “dropout” and extend operation as the battery voltage approaches discharge. LDO Regulators 4 100mA (Cout = 1.0μF) Iout = 0mA OUtput voltage (V) 50 0 3.020 3.000 2.980 2.960 100mA (Cout = 1.0μF) 100 50 OUtput voltage (V) 100 Output current (mA) Iout = 0mA ROHM TA2 Series 0 3.020 3.000 Output current (mA) Conventional 2.980 2.960 High-speed response ΔV = mV ΔV = 98mV 20 Figure 4. A high-speed load response LDO assures that the output voltage regulation can be sustained, even as the battery voltage falls as the battery is close be being fully discharged. Ripple Rejection and Circuit Footprint Ripple Rejection Characteristics LDOs are also used to power RF and analog circuitry 100 in portable consumer products. LDOs optimized for 90 Ripple Rejection (dB) high ripple rejection insure a clean output for powering these circuits. (See Figure 5.) Devices equipped with internal phase compensation provide higher levels of ripple rejection, often without the need for external filter capacitors, resulting in a simpler solution and smaller 80 70 ROHM 60 50 Conventional 40 circuit footprint. 30 Reverse Current Protection and Circuit Footprint 20 100 1K If VIN is lower than VOUT when the LDO is turned off, (due to a residual charge on the output capacitor, for example) a damaging reverse current could flow from the output to the input. A standard feature of all ROHM 10K 100K Frequency (Hz) Figure 5. Internal phase compensation significantly enhances ripple rejection without the need for external filter capacitors. Some ROHM LDOs attain rejection ratios of 70 dB and higher as shown by blue traces as compared to typical devices. CMOS LDOs is an internal circuit, as shown in Figure 6, which safely discharges the output capacitor without the need for external blocking diodes and further reduc- D2 es the overall circuit footprint. D1 Overtemperature and Overcurrent Protection and VIN Thermal Design VOUT Built-in foldback type overcurrent protection prevents STBY damage and can reduce the heating effects of current overload conditions on the LDO and surrounding cir- Discharge function cuitry. Thermal protection further restricts the device’s temperature. These protection circuits combine to limit total heating during operation and can simplify thermal Figure 6. An internal discharge circuit prevents reverse current flow and eliminates the need for diodes D1 and D2. design. ROHM Semiconductor LDO Regulators 5 ROHM Semiconductor LDO Solutions ROHM Semiconductor CMOS LDOs for portable devices provide designers several advantages including: • High-accuracy output voltage ±1% over a wide temperature range • Compatible with compact ceramic capacitors for an overall smaller footprint • Low current consumption (as low as 20 μA with the BHxxPB1 series in high-speed mode) Standard CMOS LDOs [LB1 and FB1 series] from ROHM Semiconductor have a low (40 μA) current consumption and high (70 dB) ripple rejection in a small (1.6 x 1.6 mm2) HVSOF5 package. (Also offered in the industry-standard SOT25-5 package.) The low current consumption provides extended battery life in portable applications.High ripple rejection assures a stable output for improved performance. These products provide a good starting point for many portable products, such as camcorders, notebook computers and MP3 players. • 0 μA standby current For tighter design criteria, other families extend these • Built-in foldback type overcurrent protection (See Figure 7) capabilities and add functionality for higher performance. • Built-in thermal shutdown • Built-in discharge circuit to prevent malfunction when entering standby mode or at power-on Automatic Power Saving Function LDOs [PB1 series] continuously monitor the output current and automatically select either the low current consump- • High ESD protection tion or the high-speed operation circuit depending on • Soft-start [BH6733] real time conditions as shown in Figure 8. This unique • Automatic Power Saving (APS) function to reduce power consumption during light-load conditions [BHxxPB1 series] • High (300 mA) output current [BHxxMA3 series] approach reduces operating current to just 2 μA under light-load conditions. Another design feature is the output discharge function that reduces the time duration of 0 V during start up from 1 second to 10 ms for • High ripple rejection of 70 dB or even 80 dB [BHxxNB1 series] improved stability. Inrush current protection, overcurrent protection, thermal shutdown, 1.7V operation, 1% • High-speed load response voltage accuracy and 8kV ESD protection are among • Ultra-compact molded package [BHxxTA2 series] or chip scale package [BHxxRB1 series] the added features in this product family for increased durability and performance. This family provides an These performance advantages are implemented in a excellent solution for extending the battery life in cell variety of product families (indicated above in brackets). phones and other handheld portable products. ROHM Foldback Type 3.5 3 3 Output voltage (V) Output voltage (V) Conventional Droop Type 3.5 2.5 2 1.5 1 Large short-circuit currents result in excessive heat generation 0.5 0 2.5 2 Safe against small short-circuit currents 1.5 1 0.5 100 200 300 400 0 100 Load current (mA) 200 300 400 Load current (mA) Figure 7. Foldback overcurrent protection reduces device heating during fault conditions. ROHM Semiconductor LDO Regulators 6 Measurement Conditions BH12PB1WHFV VCC = 2.2V VSEL = open, VSTBY = 1.5V Vcc Low Power Consumption LDO SW (During Standby) Fast Load Response LDO (During Normal Operation) VOUT Current monitor GND current IGND (μA) Automatic switching 30 High-speed response mode 20 10 Low consumption mode 0 0 0.5 1 1.5 2 2.5 3 Output current IOUT (mA) Hybrid system Figure 8. The automatic switching between low power consumption and fast load response modes in ROHM Semiconductor’s proprietary Automatic Power Saving (APS) function provides a power savings without compromising performance. High current [MA3 series] LDOs include a proprietary ROHM feedback circuit, low ON-resistance, and two parallel 100mA (Cout = 1.0μF) output terminals (see Figure 9) to enable stable load 100 50 OUtput voltage (V) regulation as low as 6 mV compared to conventional regulators at 30 mV. The compact (1.6 x 3.0 mm2) high power (Pd = 680 mW) HVSOF6 package has an underside heatsink for high thermal dissipation. In addition to 0 3.020 3.000 OUtput current mA) Iout = 0mA 2.980 2.960 higher power loads in battery-powered products, this High-speed response ΔV = mV 20 higher current LDO can handle loads in graphics cards, Iout = 0mA 100mA (Cout = 1.0μF) HDTVs. 100 Output voltage (V) 50 Only 6mV 0.6Ω low ON resistance FET Output voltage (V) Dual output terminal 3.0 ROHM 30mV 100 200 3.000 2.980 2.960 ΔV = 98mV Conventional 0 0 3.020 OUtput current (mA) Conventional telecom equipment and consumer applications such as 300 Load current (mA) Figure 9. ROHM’s MA3 series LDOs exhibit a voltage drop of just 6 mV (IOut = 100 mA) instead of 30 mV in comparable devices. Figure 10. High-speed load regulation reduces load response from nearly 100 MV to only 20 MV with an output step-change from 0 to 100 mA. SSON004X1216 (1.6 x 1.2 x 0.6 mm3) package, TA2 series devices are 25% smaller than the HSVOF5. Ideal for high-speed processing and data reading in High speed load response [TA2 series] LDOs high-density logic and memory applications, these reduce the fast load response to just 20 mV while transitoning from 0 to 100 mA output current compared to conventional regulator values of up to 98 mV as shown in Figure 10. Offered in the ultra compact ROHM Semiconductor LDOs are frequently used in portable audio circuits and in digital cameras as well as portable computers, PC mother boards and graphic cards. LDO Regulators 7 a b CSP Construction SOT23-5 (SSOP5) VCSP60N1 2.8 Power dissipation 540mW Ultra-thin Cu POST construction compatible with PCBs No cracking during installation 1.0 (when mounted on a substrate) Mounting area 1.04 1 8 0.6 Overcoat 2.9 POST structure Silicon 0.6 mm Thickness 1.25 4X magnification Actual size PCB [Unit : mm] Small solder balls can be attached to prevent problems during installation Figure 11. LDO products in the Chip Scale Package (CSP) (a) occupy 1/8 the mounting area of a SOT23-5 package and (b) utilize sophisticated packaging techniques to avoid reliability problems during assembly. High ripple rejection [NB1 series] provide an addi- tions under the most severe space constraints such as tional 10 dB of margin for a total 80 dB at 1 KHz and smart cell phones and digital cameras. improved ripple rejection over a broader frequency The three-channel output, BU665xNUX Series range. These units also have 6 mV load regulation combines a number of the advantages of the single- and 1 mV line regulation ensuring stable power supply channel ROHM CMOS LDOs while providing three operation even in applications with significantly varying independent outputs in a single, compact device that load currents. In addition, proprietary phase compensa- reduces mounting costs and board wiring. Three com- tion circuitry in the design may eliminate the need for an binations of output voltages are offered, each with 200 external capacitor providing space reduction and lower mA per channel output current (Pd = 660W, max.), low system cost. This family provides improved line and current consumption and ON/OFF control for each load regulation for analog applications in portable prod- channel as well as 1% output voltage tolerance, over- ucts such as sensor and audio applications common in current protection and thermal shutdown. cell phones, camcorders and digital cameras. The Chip Scale Package (CSP) [RB1 series] pro- Conclusion vides an even smaller footprint than ultra-small molded As battery powered, wireless products proliferate, packages. The 4-pin CSP shown in Figure 11(a) mea- system designers can continue to count on LDOs for 3 suring 1.04 x 1.0 x 0.6 mm , just slightly larger than the regulated power sources with low noise and space sav- chip itself, has a mounting area that occupies only /8 ing design. Specifically designed for low power appli- of the PCB space of a standard 2.8 x 2.9 x1.25-mm3 cations in portable products, ROHM Semiconductor SOT23-5. Increased performance capabilities come CMOS LDOs provide a variety of solutions for efficient from the RB1 series’ low input/output voltage difference and cost-effective power management. Package size, of 100 mV @ Io=100 mA, and current consumption as power efficiency, dynamic regulation and ripple rejec- low as 34 μA making it highly desirable in lower input tion are among the features that should be considered voltage applications. As shown in Figure 11(b), CSP in making an LDO selection. ROHM Semiconductor’s technology includes design considerations that improve complete line of CMOS LDOs combined with expert reliability and minimize end product manufacturing application engineering support assures the optimum problems. The RB1 series is ideal for portable applica- choice for every application. 1 ROHM Semiconductor LDO Regulators 8 10145 Pacific Heights Blvd., Suite 1000 San Diego, CA 92121 www.rohmsemiconductor.com | 1.888.775.ROHM NOTE: For the most current product information, contact a ROHM sales representative in your area. ROHM assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representations that the circuits are free from patent infringement. Specifications subject to change without notice for the purpose of improvement. The products listed in this catalog are designed to be used with ordinary electronic equipment or devices (such as audio visual equipment, office-automation equipment, communications devices, electrical appliances and electronic toys). Should you intend to use these products with equipment or devices which require an extremely high level of reliability and the malfunction of which would directly endanger human life (such as medical instruments, transportation equipment, aerospace machinery, nuclear-reactor controllers, fuel controllers and other safety devices), please be sure to consult with our sales representative in advance. © 2009 ROHM Semiconductor USA, LLC. Although every effort has been made to ensure accuracy, ROHM accepts no responsibility for errors or omissions. Specifications and product availability may be revised without notice. No part of this document represents an offer or contract. Industry part numbers, where specified, are given as an approximate comparative guide to circuit function only. Consult ROHM prior to use of components in safety, health or life-critical systems. All trademarks acknowledged. CNA09017_wp