July, 2009
Ultra-Low Voltage DC-DC Converter Capability John Pigott, Analog IC Design Kevin Parmenter, Applications Engineering Manager TM
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Agenda ► Introduction
– what challenges are we solving?
► Applications •
Solar, Thermal, Chemical …
► Issues
of parallel – series connections ► Overview of demonstrated solution • • •
Circuit Process Efficiency – technology
► Technical detail ►Q
of IC & circuits
&A
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What Are We Introducing? A new power conversion capability for solar applications and demonstration of an ultralow-voltage DC-to-DC converter IC designed to enable industry-leading efficiency for single-cell photovoltaic DC-DC converters Ultra-low-voltage converter High energy efficiency
Lowest startup and operating voltage DC-DC converter demonstrated 320 mV or lower
Up to 90% conversion efficiency
Advanced technology
82% in solar applications, 90% in others SMARTMOS™10W 130 nm enables the ULV startup and operating efficiency
Presently most suitable for 100 mW to 1 W applications
Low parasitic losses enabled by custom flip chip on lead frame (FCOL) package
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Freescale’s Analog Technology Leadership ► Freescale
offers more than 50 years of innovation in semiconductors and more than 25 years in the high-performance analog market ► Freescale ranked #7 in global analog sales (Source: Databeans 2007) ► Consumers expect everything to be intelligent and connected •
Need high-performance analog circuitry
► Industry-leading, •
differentiated SMARTMOS process technology
Integrates digital, power and standard analog functions in a single device
► Highly
integrated System on Chip (SoC) and System in Package (SiP) solutions ► Development tools and 24/7 customer support ► Freescale has a compelling portfolio of analog and power management solutions for the consumer, industrial and automotive markets
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Target Applications for ULV Power Conversion Technology ► Power
conversion and energy recovery applications involving ultra-low voltages ► Energy-harvesting applications, such as thermoelectric, mechanical scavenging systems, and parasitic power ► Potential applications include: • • • • • • • •
Solar-powered battery chargers Trickle chargers for automotive systems Chargers for cell phones and laptops Remote data acquisition and monitoring Self-powered wireless transponders Industrial HVAC systems PV-based traffic signals, ocean markers, airports Solar-powered rural lighting products
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Practical Issues With Series – Parallel Connections ► Connection
in series allows boosting the low voltage sources to more common voltage levels; however: • • •
• • •
Some sources either will not series or behave unstably when you do Example solar cells in series – increased voltage, but current is limited by lowest output (shading/temperature/mismatches) in the series string Parallel – increases current – however voltage sources fight each other and will not current share well – power is limited by the lowest voltage source. Parallel connections will not increase voltages Electrochemical sources – it may be impossible or very cumbersome to series connect Thermopiles are often series connected – increases physical size, mechanical complexity and cost Architecture of input-regulating converter for boost makes it easier to parallel outputs if necessary
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Challenges of Ultra Voltage Power Conversion ► Ultra
Low Voltage 250 mV – 700 mV ► Interconnect voltages drops – packaging parasitics AC & DC can become a significant source of loss ► Process technologies which operate below 0.7 volts and allow design of high performance circuits ► Conversion efficiency–if you can make it work at all ► Low quiescent current ► Power control topology—power-limited sources have a different requirement for the control loop architecture ► Design techniques at low voltages ► Integrating complete boost conversion •
Demonstrated solution has only 3 external components—input decoupling capacitor, output decoupling capacitor and an inductor
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Addressing Application Needs Technology Attribute
Benefit
Ultra-low voltage start up and operation
Enables the utilization of a low-voltage source such as a single photo cells rather than requiring an array. Thermoelectric or other low voltages sourced can be converted directly. Autonomous start without external sources.
Power efficiency
Preserves a higher amount of power being converted for delivering more energy to the load.
Packaging
Provides low DC resistance and low inductance helping with conversion efficiency. Small size enables beneficial for products.
• Single solar cell, or smaller thermopile stack simplifies mechanical construction • Single solar cell much less sensitive to shading, cell balancing • High efficiency reduces solar cell area or thermopile size needed • Very small size (package is < 6 mm²) enables smart dust applications Opens up new possibilities in power conversion previously unavailable or discounted
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Demonstrated Device
Freescale
Power Source
Load
ULV DC/DC Converter
NC
3 x 2 mm 10-pin DFN package
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Power Conversion Technology Demonstration
This is a technology demonstrator, not a released product. Freescale is actively seeking input from potential users to determine precisely what features are desirable in a product.
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Single Solar Cell Operation ► VIN
= 384 mV ► IIN = 1.36A ► VOUT = 4.04 V ► IOUT = 103 mA Efficiency: 80%
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Efficiency Measurements (VIN 0.45 V and 0.7 V) Efficiency vs. Output Power 95%
Efficiency
90%
85%
VIN ~ 0.45 V
80%
VIN ~0.7V
75% 0.0
0.2
0.4
0.6
0.8
1.0
1.2
Output Power (W)
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Demonstration IC in PV Application ► Photovoltaic (PV)
and other applications with power-limited sources often cannot be used in a DC-DC converter system with an outputregulated control loop •
Freescale Load
This is because a DC-DC converter with a constant load (constant power load) appears to have a negative input impedance, and when the power available from the source is less than the connected load power, the system becomes unstable and the input voltage collapses
► This demonstration
Power Source
IC includes two features
ULV DC/DC Converter
VOUT
LX
to prevent this
Fixed maximum duty cycle (approximately 93%) which makes the regulator act as a DC transformer (fixed ratio between VOUT and VIN. This does not have a negative input impedance and therefore is stable • Input Regulator (VIN-SET) which regulates the duty cycle so that the input voltage does not fall below a desired threshold. This connection can also be used as part of a Maximum Power Point Transfer (MPPT) control loop
Internal Bias
•
Boost Driver
UVLO Crossove r
.
R2
Vref1
+
VIN
M1
Bootstrap
M2
93% Max Duty Cycle
Oscillator
Ramp Generator
+ Cboot . -
VIN-SET
-
GND
.
gm +
System Control
Vref2 (0.315V)
LED Driver LED
Test Modes
N/C
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R1
7mA
CELLGND
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Demonstration IC Under Source Power-Limited Conditions Pulse Skipping VOUT ~ 5.5 V
86% Fixed Duty Cycle VOUT:VIN = 5.5:1
Constant Power VIN = 0.64 V
6
1.8 IIN reaches its maximum (1.6 A)
5
1.5
Vout (V)
Light-Load VOUT 4
1.2
3
0.9 Efficiency (76-90%)
2
Vin (V), Iin (A)
VOUT reaches its minimum (2.8 V)
0.6
VIN reaches its minimum (0.64 V)
1
0
0.3
0 0
50
100
150 Load (mA)
200
250
300
VIN, IIN and VOUT vs. Load; VSOURCE ~ 1.05 V (This version of the IC has a fixed 86% duty cycle)
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MPPT Demo Charging Li-Ion
►
MCU is powered from VOUT (2.7..5V) MCU monitors load current (via GND R and 10-bit ADC) •
►
Opamp + FET are current source to adjust VIN/VINSET value • • • • •
►
►
►
Could use FET RDSON ?
VIN = VINSET + I*R2 VINSET ~ 0.315V I = VPWM / R4 Adjustment via PWM MCU searches around VIN to get peak current in R1
May need additional comparator to detect when VDD < VLOAD and prevent discharge Overcharge can be stopped by high current at VINSET – will force a high VIN which is not possible with solar cell DC/DC will stop Algorithm and implementation will be integrated in future generation of ULV DC/DC
VLOAD
VDD Freescale
Power Source
ULV DC/DC Converter
VSS
R1
R2
MC9S08QD4
►
R3 + . -
VDD VSS
R4
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Demonstration IC Description ► Internal
8x charge pump generates over 2 V to power bootstrap
circuits •
Fully internal charge pump runs at 10 MHz
Bias, Logic, control all run from VIN of 0.32 V
► Bootstrap
circuit pulses inductor at ~ 15 kHz to drive VOUT to ~ 2.5
V •
Load is disconnected at this stage
► UVLO
Crossover circuit detects VOUT reaching 2.9 V and turns on main DC/DC converter • •
Main DC/DC is powered from the output voltage, so there is no fundamental limit to how low VIN can go after startup Practically, there is little use in a DC/DC system which operates at an input voltage of lower than 50% of the open circuit voltage (because maximum power transfer point has been crossed)
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Simplified Block Diagram
Vin 0.3V – 1.0V
Disable
Ultra Low Voltage Boot Driver 0.32V; 10-50µA
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PWM Controller and Regulator 3-5V 160µA – 6mA
Enable VREF
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Potential Low Power, Ultra-Low Voltage System ► This technology
is scalable to lower and higher power systems ► Potential capability of an ultra low power energy harvesting system could be as follows: ► Bias •
10 µA 5 µA; perhaps with some limitation on high temperature operation
► Charge •
Pump
40 µA 10 µA
Slower startup; VOUT limited to 3.3V
► DC/DC •
Pulse-skipping DC/DC converter with > 85% conversion efficiency
► Capability
0.32V startup, 3.3 or 4.2 V output • < 10 µW quiescent consumption • 3.3V output, ~ 20mW • Suitable for indoors PV or TEG systems •
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FCOL: Custom LF Concept
Freescale Bumped Die
Custom Leadframe
Carsem FCOL Datasheet
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SMOS10W: The Most Comprehensive Portable Power Management Technology Trimming
• Low current fuses for customization, calibration and trimming
Memory
• MRAM option with unlimited
Isolation
endurance
• P- substrate for improved •
ground noise immunity Buried layer-isolation structure for signal isolation and latch-up immunity
Voltage
SMARTMOS10
• 28V NLDMOS for serial LED backlight
Analog
Digital
• Mismatch 0.3-0.5x on FETs,
• High speed for USB2.0 • Low leakage for coin cell life
resistors & caps for analog shrink & audio quality.
Power
extension
• >100K gates/mm² for size
• 125°C leakage 20x lower •
reduction
for extended battery life Ron*Area 60% lower for size reduction
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Q&A ► Thank
you for attending this presentation. We’ll now take a few moments for the audience’s questions and then we’ll begin the question and answer session.
Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2009.
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