The document is a presentation about power management fundamentals from Analog Devices. It discusses different types of power conversion and regulation products like linear voltage regulators and switching regulators. It explains the need for stable, clean power supplies to avoid noise and errors in high-precision systems. Key topics covered include linear regulators, switching regulators, power distribution, minimizing noise and ripple, and tips for successful power design. The presentation is part of Analog Devices' 2011 webcast series on signal processing fundamentals.

1. The World Leader in High Performance Signal Processing Solutions
Power Management
Fundamentals
July 2011 Webcast

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’ Series
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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 operation
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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 supervisors
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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 Regulator
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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 off
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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/division
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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))
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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)
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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
ADP150
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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 = 0.75V
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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 = 3.3V
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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
Analog
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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 Cost
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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 outputs
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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.
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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 High
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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)
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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 PSRR
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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 @ 100kHz
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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 circuits
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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-regulator
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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 less
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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
www.analog.com/webcast
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