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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.
Ultra-Low Voltage DC-DC Converter Capability
July, 2009
John Pigott, Analog IC DesignKevin Parmenter, Applications Engineering Manager
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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 of IC & circuits►Q & A
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What Are We Introducing?
Up to 90% conversion efficiency
82% in solar applications, 90% in others
Presently most suitable for 100 mW to 1 W applications
Lowest startup and operating voltage DC-DC converter demonstrated
320 mV or lowerSMARTMOS™10W 130 nm enables the ULV startup and operating efficiency
Low parasitic losses enabled by custom flip chip on lead frame (FCOL) package
A new power conversion capability for solar applications and demonstration of an ultra-low-voltage DC-to-DC converter IC designed to enable industry-leading efficiency for
single-cell photovoltaic DC-DC converters
Ultra-low-voltage converter
Advanced technology
High energy efficiency
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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
Preserves a higher amount of power being converted for delivering more energy to the load.
Power efficiency
BenefitTechnology Attribute
Provides low DC resistance and low inductance helping with conversion efficiency. Small size enables beneficial for products.
Packaging
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.
Ultra-low voltage start up and operation
• 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
3 x 2 mm 10-pin DFN package
Freescale
ULV DC/DC Converter
LoadPower Source
NC
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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 mAEfficiency: 80%
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Efficiency Measurements (VIN 0.45 V and 0.7 V)
Efficiency vs. Output Power
75%
80%
85%
90%
95%
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Output Power (W)
Effic
ienc
y
VIN ~ 0.45 VVIN ~0.7V
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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 output-regulated control loop
• 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 IC includes two features 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
Freescale
ULV DC/DC Converter
LoadPower Source
+
-
.
R1
Cboot
Bootstrap
Oscillator
Boost Driver
R2
+
-
.
+
-
.
VINVref1
Test Modes
93% Max
gm
UVLOCrossove
r
GND
Internal
Duty Cycle
7mA
LED Driver
CELLGND
VOUT
LED
LX
Bias
VIN-SET
(0.315V)Vref2
System Control
RampGenerator
M2M1
N/C
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Demonstration IC Under Source Power-Limited Conditions
VIN, IIN and VOUT vs. Load; VSOURCE ~ 1.05 V(This version of the IC has a fixed 86% duty cycle)
0
1
2
3
4
5
6
0 50 100 150 200 250 300Load (mA)
Vout
(V)
0
0.3
0.6
0.9
1.2
1.5
1.8
Vin
(V),
Iin (A
)
VOUT reaches its minimum(2.8 V)
VIN reaches its minimum(0.64 V)
Light-Load VOUT
IIN reaches its maximum(1.6 A)
Efficiency (76-90%)
Pulse SkippingVOUT ~ 5.5 V
86% Fixed Duty CycleVOUT:VIN = 5.5:1
Constant PowerVIN = 0.64 V
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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)
• Could use FET RDSON ?► Opamp + FET are current source to
adjust VIN/VINSET value• 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
Freescale
ULV DC/DC Converter
Power Source
VDD
VSS
R2
R1
VLOAD
VDDVSS
+
-
.
R3
R4 MC
9S08
QD
4
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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
Ultra Low Voltage Boot Driver
0.32V; 10-50µA
PWM Controller and
Regulator3-5V
160µA – 6mA
VREF
EnableDisable
Vin0.3V – 1.0V
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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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Custom Leadframe
Freescale Bumped Die
FCOL: Custom LF Concept
Carsem FCOL Datasheet
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SMOS10W: The Most Comprehensive Portable Power Management Technology
SMARTMOS10Voltage
• 28V NLDMOS for serial LED backlight
Digital• High speed for USB2.0• Low leakage for coin cell life
extension• >100K gates/mm² for size
reduction
Power• 125°C leakage 20x lower
for extended battery life• Ron*Area 60% lower for
size reduction
Analog• Mismatch 0.3-0.5x on FETs,
resistors & caps for analog shrink & audio quality.
Memory• MRAM option with unlimited
endurance
Trimming• Low current fuses for
customization, calibration and trimming
Isolation• P- substrate for improved
ground noise immunity• Buried layer-isolation
structure for signal isolation and latch-up immunity
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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.
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