1. Understanding Power Supply Basics and Terminology
DC/DC Converters 101
Understanding Power Supply Basics and Terminology

2. Agenda Lecture Overview Linear Regulators Switching Power Supplies
Topologies
Synchronous vs. Non-synchronous
Controller vs. Converter
Selecting the Best Power Solution

3. Why should I care about power?
1. Every electronic system uses power.
2. Your power source never matches your system needs.
Power Source
DC/DC Supply
gets you from
here to there
What you need
Typically
5V,12V or 24V
6.0Vdc-16Vdc
40Vdc Surge
1.2V 2A
2.5V 1.2A
3.3V 5V
+/-12V
3.0Vdc-4.2Vdc

4. Linear Regulators vs. Switching Supplies
Pass element operates in the linear region
Down conversion only
Switching Power Supply
Pass elements switch, turning fully on/off each cycle
Filtering includes an inductor
Multiple topologies (Buck, Boost, Buck-boost…)

5. Linear Regulator ADVANTAGES: DISADVANTAGES: APPLICATIONS:
Low O/P ripple & noise
Fast transient response
Low cost (for low power, at least)
Easy to design
No EMI to worry about
DISADVANTAGES:
Low efficiency at VIN>>VOUT
High dissipation (needs large heat-sink)
VOUT<VIN – always!
APPLICATIONS:
Extremely low ripple & noise apps
Low input to output voltage difference
Tight regulation

6. Dropout Voltage
Dropout (headroom): The minimum required voltage across an LDO to maintain regulation
Example:
Vin = 3.1V to 4.2V
Vout = 100mA
Need at least 600mV headroom
+ Vdo -

7. Linear Regulator vs LDO
Linear Regulator has Higher Dropout Voltage.
Transistor or Darlington pair pass element
LM317 (1.5A linear regulator)
1.5V to 2.5V dropout voltage
Good for larger Vin to Vout ratios, 12V to 5V output
CHEAP!!!
LDO = Low Dropout Regulator
Typically higher performance
PSRR, regulation tolerance, transient response, etc
MOSFET pass element
TPS72501 (1A LDO)
170mV dropout voltage
Good for 3.3V to 3.0V output

8. Linear Regulator Power Dissipation
Input Current = Output Current
Power Loss = Iout * (Vin – Vout)
Power loss is usually a limiting factor!

9. Linear Regulator vs Switcher
2.5W LDO +
ground plane
as heat sink
6W Switcher

10. Switcher DC DC ADVANTAGES: High efficiency VOUT>=<VIN
Wide input voltage range
Low power dissipation (small heatsink)
High Watt/cm2
Isolation possible (with transformer)
Multiple O/Ps possible (with transformer)
DISADVANTAGES:
EMI
Slower transient response
More difficult to design
Higher output ripple & noise
APPLICATIONS:
High efficiency power supplies
High ambient temperatures
Large input to output voltage difference
Space constraints
High output power DC
VIN
VOUT DC

11. Basic Topologies
Buck
VIN
VOUT
Boost
VIN
VOUT
Buck/Boost
VIN
VOUT

12. Synchronous vs Non Sync
Non-Synchronous Buck
Non-synchronous
Diode voltage drop is fairly constant with output current
Less efficient
Less expensive
Used with higher output voltages
Synchronous
MOSFET has lower voltage drop
More efficient
Requires additional control circuitry
Costs more
Synchronous Buck

13. Synchronous vs Non Sync
Vin=5V
Vout=1V Rdson_sync=0.12ohm Vf_diode=0.5V
Iout=1A
1V Output Synchronous
1V Output Non-Synchronous
Sync vs Non-sync is less of an issue with higher Vout
Higher duty cycles = less power dissipation in Sync FET or Catch Diode

14. Synchronous vs Non Sync
Power FET
Synchronous FET

15. Synchronous vs Non Sync
Integrated Power FETs
Rectifier Diodes
Integrated Power FET
and synchronous FET

16. Controller vs Converter
Discrete MOSFETs
Provides the “brains” to control the power stage
More complicated to design
Full control over FET selection, switching frequency, overcurrent, compensation, softstart
Can tailor the power supply to meet your specific needs
Converter (Fully integrated)
Integrated switches
“plug and play” design
Limited range of output filter components
Limited control over functionality
Converter (Partially integrated)
May offer full or partial feature set , internal or external compensation
Internal Power FET, external sync-FET or catch diode
Limited control over frequency, overcurrent, softstart, etc
Allows wider range of output filter components

17. Converter (Fully Integrated)
TPS62293
2.3V to 6V input
1A Output Current
2.25MHz
Everything is integrated, minimum external components

18. Converter (Partially Integrated)
TPS54620
4.5V to 17V input
6A Output Current
Internal FETs, external SoftStart, Compensation, Frequency set… more flexibility
Set frequency
Compensation

19. Controller TPS40303/4/5 3V to 20V input 10A Output Current
300kHz to 1.2MHz
External FETs
Compensation
Softstart
Current limit

20. Size vs. Cost vs. Efficiency
Synchronous
Non-synchronous
Linear Regulator
Power
Density
Cost
Converter (Fully Integrated)
Converter (Partially Integrated)
Controller

21. Efficiency vs Vout Efficiency depends on output voltage?
Why isn’t MY supply 95% efficient?
The datasheet says:

22. Efficiency vs Vout 3.3V Output 1V Output Power FET Conduction Losses
Simplified power dissipation equations assuming no inductor current ripple
3.3V Output
1V Output
Power FET Conduction Losses
Sync FET Conduction Losses
Total FET Losses
(does not include other circuit losses)
0.173 W
0.136 W

23. Efficiency vs Vout
3.3V Output
1V Output

24. PWM vs PFM Pulse Width Modulation Pulse Frequency Modulation
Constant frequency
Low output voltage ripple
Used with high output currents
Pulse Frequency Modulation
Varying frequency with Vin and load
Very high efficiency at very light loads
Higher output voltage ripple
Potential operation in audio range

25. PWM vs PFM
PFM mode
PWM mode

26. Startup - Softstart Slowly turning on the power supply
Controlled rise of output voltage
Minimizes inrush currents
Minimizes system level voltage drops
Pulling high currents out of input bus
High impedance batteries
Internal vs SS capacitor
Larger SS capacitor = longer softstart time

27. Startup - Sequencing Sequencing Sequential sequencing
Controlling the order that different power supplies are turned on
Important for uP loads
Minimizing overall inrush current
Sequential sequencing

28. Startup - Sequencing
Ratiometric Sequencing
Simultaneous Sequencing

29. Easy Answers – Power Quick Search
Provides a list of possible linear regulators, controllers and converters based on inputs
Great starting point for selecting a device

30. Easy Answers – Power Quick Search

31. More Answers – Browse The Product Tree

32. Easy (Simulated) Answers – WEBench
Provides a complete design based on inputs
Best for customers with little or no power background

33. Easy (Real) Answers – TI Designs/PowerLAB
Searches reference designs based on input

34. THANKS!!
Questions???