Adi jul1311


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Adi jul1311

  1. 1. The World Leader in High Performance Signal Processing SolutionsPower Management Fundamentals July 2011 Webcast
  2. 2. Power Management Fundamentals Agenda  What is Power Management?  Types of Power Conversion Products  The Need for “Clean” & Stable Power Supplies  What is a Linear Voltage Regulator?  Why use a Linear Regulator over a Switching Regulator?  Common Types of Switching Regulator  DC Power Distribution  The Road to Successful Power Designs  Upcoming webcasts in the ‘Fundamentals’ Series2 —Analog Devices Confidential Information—
  3. 3. What is Power Management?  All Electronic systems require a power supply & some form of power management. System power needs vary from simple 3-terminal regulators, to sophisticated IC voltage regulators providing multiple outputs. In addition, high-performance systems may require continuous monitoring of power-supply voltages & currents during operation3 —Analog Devices Confidential Information—
  4. 4. What is Power Management? contd.  What functions are included in Power & System Management  Power conversion products; Low dropout regulators, switching regulators, switching controllers  Power switches or Load switches  Supply voltage monitoring  Supply voltage sequencing and tracking  Battery switchover devices  Hot-swap controllers  Supervisory products; reset controllers, watchdog timers, multi-voltage supervisors4 —Analog Devices Confidential Information—
  5. 5. Power Conversion Products  Nearly all electronic equipment is powered from low voltage DC supplies. The power source is either a battery, a combination of battery & DC/DC converter, or a power supply converting AC mains into low voltage DC supplies, suitable for electronic components  Electronic components require:  DC supply that is well regulated  Low output noise and ripple  Fast transient response to load changes  AC power supplies, & some DC/DC converters, provide isolation from the input to the output for safety, noise reduction, & transient protection  There are two types of DC/DC conversion in common use: 1. The Linear Voltage Regulator 2. The Switching Regulator5 —Analog Devices Confidential Information—
  6. 6. Key Regulator Specs & their Significance  Input Voltage (Vin) Range  The voltage range over which a regulator is specified for normal operation  Output Voltage (Vout) & Output Current  The factory-set output voltage & the maximum current available from this output  Output Voltage Accuracy & Drift  Accuracy of the factory-set output voltage, specified in mV or % of output at 25C. Drift is the change in DC output voltage over the operating temperature range  Dropout Voltage  Dropout voltage is a term specific to LDOs and is the minimum Vin-Vout differential voltage necessary for correct LDO operation at a specified load current  Output Noise  Noise generated by the regulator itself is specified as broadband or peak-peak  Power Supply Rejection Ratio (PSRR)  The ability of a regulator to reject a large voltage change at it’s input and produce a small change at it’s output. Usually specified in dB for DC input changes  Quiescent Current & Shutdown Current  Quiescent current is the current drawn by the regulator when there is no load current. Shutdown current is the current drawn when the regulator is disabled, or powered off6 —Analog Devices Confidential Information—
  7. 7. The Need for “Clean” & Stable Power Supplies  Regulators are available in different levels of performance from ‘commodity’ to specialized high-performance types  In low-performance systems, commodity LDOs & switching regulators may work fine. However, systems that use high-resolution (12-Bit & higher) converters may experience performance degradation if powered by commodity regulators  Commodity switching regulators tend to be; less efficient, require larger external components, & may offer less protection under fault conditions compared to high-performance switching regulators Output Noise from a Switching Regulator, 10mV/division7 —Analog Devices Confidential Information—
  8. 8. The Need for “Clean” & Stable Power Supplies contd.  Which voltage regulator parameters can compromise system performance? Voltage drift, noise, and ripple on the regulator’s output are primary causes of signal distortion & measurement errors caused by the supply  How do drift, noise, & ripple get into the signal-chain? They are conductively coupled from the power supply directly to the ‘victim’ circuits, e.g. op amp, reference, ADC, etc. however, the signal is reduced by the power supply rejection ratio (PSRR) of the ICs  How do you quantify PSRR? PSRR is the ratio of the DC change in power-supply voltage to the resulting change in the load IC’s gain, offset, or other errors. PSRR can be expressed in fractions of a least significant bit (LSB) for an ADC, a percentage, or in dB (PSR = 20 × log10 (PSRR))8 —Analog Devices Confidential Information—
  9. 9. What is a Linear Voltage Regulator? A Linear Voltage Regulator is any device that reduces a voltage in a dissipative manner for the purpose of regulation  Includes Zener diodes (or regular diodes) and shunt references  Generally a closed-loop system with a transistor operating in its linear region  Can only reduce voltage, can’t boost it  Non-Isolated output  Efficiency is directly proportional to Vout/Vin (neglecting bias current loss)9 —Analog Devices Confidential Information—
  10. 10. Low-Noise LDOs for ADC, RF, & PLL Power  The150mA ADP150 & 200mA ADP151 are ultra-low noise (9µV rms) LDOs suitable for powering the most sensitive circuits such as high-resolution ADCs & low-noise PLLs ADP15010 —Analog Devices Confidential Information—
  11. 11. LDOs with Excellent High-Frequency PSRR  The 800mA ADP1752-53 and 1.2A ADP1754-55 are low- voltage LDOs with high PSRR (65dB) & low-noise for post- switcher applications. Input voltage range is 1.6V to 3.6V ADP1752 Output Noise ADP1752 PSRR, Vout = 0.75V11 —Analog Devices Confidential Information—
  12. 12. Micro-Power LDOs for Portable Applications  The ADP160 is a micro-power LDO optimized for battery powered & portable applications. Quiescent current is typically 560nA @ 0µA load, & only 3µA with a 100µA load. PSRR is typically 60dB @ 100Hz, a reduction of 1000:1 ADP160 LDO Ground Current ADP160 LDO PSRR Vout = 3.3V12 —Analog Devices Confidential Information—
  13. 13. Cleaning the Output of a Boost Regulator in a Battery Powered Application Better than 40dB Ripple Rejection 100mV/ 20mV/ DIV DIV 1.5V to 0.9V ADP162 Single Cell Low IQ Boost 3.3V 2.8V LDO Regulator High Performance Analog13 —Analog Devices Confidential Information—
  14. 14. Why choose a Linear Voltage Regulator over a Switching Regulator?  Easy to Use, three terminal device  Lower parts count  Little to no compensation needed  Lower Output Noise  Lower Input and Output ripple  No high dI/dt or dV/dt loops or nodes to radiate noise (EMI)  In some situations LDOs can achieve similar efficiencies  Light-loadefficiency is often better than a switcher’s  High Vout/Vin ratio (near dropout) means high efficiency  Specialized types available  Lower Cost14 —Analog Devices Confidential Information—
  15. 15. Most Common Switching Regulators  Buck or Step-down Regulator, Vin > Vout  Buck-Boost Regulator (invert), Vout is opposite polarity to Vin  Boost or Step-up Regulator, Vin < Vout  Flyback Regulator, Vin < Vout or Vin > Vout, can have multiple outputs15 —Analog Devices Confidential Information—
  16. 16. Low-Noise Switching Regulators  TheADP2114 & ADP2116 are dual buck (step-down) regulators with ‘reduced EMI drive’ to enable powering of sensitive signal-chain components; Op Amp, ADC, etc.16 —Analog Devices Confidential Information—
  17. 17. Summary Comparison of Linear Regulators & Switch-Mode Regulators Parameter Linear Regulator Switch-Mode Regulator Efficiency Low, <80% High, 80% to 95%+ Output Noise and Low Noise Higher noise than LDO Ripple No switching ripple Ripple at switching frequency+ Design Complexity Simple More Complex PCB Area Small, 3 components Medium, 5+ components EMI Minimal Medium (depends on switching frequency and PCB layout) Cost Low to Medium Medium to High17 —Analog Devices Confidential Information—
  18. 18. DC Power Distribution  Systems frequently require multiple power supplies for analog, digital I/O, CPU, FPGA, displays, etc.  Due to fast-changing load currents (e.g. in FPGAs & CPUs), and the need to provide good load transient response, DC/DC converters are placed adjacent to the load rather than routing a power cable from a distant supply  The requirement for local DC/DC regulation has driven the popularity of the Distributed Power Architecture (DPA)18 —Analog Devices Confidential Information—
  19. 19. How do DC Drift, Noise, & Ripple get into the Signal-Chain?  DC drift, noise, & ripple from the power supply is conductively coupled into the supply pins of the load ICs but the magnitude is reduced by the PSRR of these loads. Note that PSRR is highly frequency dependent so HF noise from switching regulators has to be controlled Low-Frequency Op Amp PSRR High-Frequency Op Amp PSRR19 —Analog Devices Confidential Information—
  20. 20. How do DC Drift, Noise, & Ripple get into the Signal-Chain?  As switching regulators replace linear regulators (for higher efficiency) the effects of HF power-supply ripple & noise must be calculated. The graphs below show the difference in PSRR performance between a commodity LDO and a high-performance LDO Commodity LDO PSRR, <30dB @ 100kHz ADP123 LDO PSRR, >60dB @ 100kHz20 —Analog Devices Confidential Information—
  21. 21. How to Minimize Ripple & Noise?  Switchingpower-supply ripple & noise can be dramatically reduced by using high-performance LDO post-regulators for the most sensitive Analog & Mixed-Signal circuits21 —Analog Devices Confidential Information—
  22. 22. The Road to Successful Power Designs  Select the voltage regulator type(s) that convert the input voltage to the output voltage(s) required, e.g. buck regulator, boost regulator, SEPIC. Ensure the outputs meet or exceed the load current requirements  Determine if a specialized regulator is required for the application, e.g. a low- noise LDO to power a high-performance 14-Bit ADC  When a switching regulator provides a high output current that also needs to have low voltage-noise, consider using an LDO post-regulator to clean up the switching noise with only a small reduction in overall efficiency Buck Regulator with Low-Noise LDO post-regulator22 —Analog Devices Confidential Information—
  23. 23. The Road to Successful Power Designs contd.  For switching regulators, follow the manufacturer’s PCB layout recommendations to ensure optimum results. PCB layout is shown in the product datasheet on ADI’s switching regulators  Calculate the temperature rise for high-dissipation parts & verify that Trise + Tamb for all parts is within the safe operating range  Use High-Quality passives (L, C, & R) for best efficiency & output accuracy. High Quality means components that are accurate & stable vs. temperature & applied voltage. HQ passives ensure HQ results 1. When using multi-layer ceramic capacitors (MLCC), use types with the X5R or X7R dielectric. Y5V & Z5U dielectrics are not recommended due to their poor temperature coefficient & DC bias characteristics 2. Inductors used in switching regulators should have; good magnetic shielding, low DC resistance, low self-capacitance, low leakage inductance, high saturation current, and a “Soft” Saturation Curve 3. Resistors used for setting output voltage should be accurate to 1% or better & have a temperature coefficient of 100ppm/C or less23 —Analog Devices Confidential Information—
  24. 24. Fundamentals Webcasts 2011 January Introduction and Fundamentals of Sensors February The Op Amp March Beyond the Op Amp April Converters, Part 1, Understanding Sampled Data Systems May Converters, Part 2, Digital-to-Analog Converters June Converters, Part 3, Analog-to-Digital Converters July Powering your circuit August RF: Making your circuit mobile September Fundamentals of DSP/Embedded System design October Challenges in Industrial Design November Designing with MEMS December Tips and Tricks for PC Board Layout —Analog Devices Confidential Information—