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JUN 2011

P o w e r i n g Y o u r S u c c e s s. Designing Charge Pump Based Converters. JUN 2011. P o w e r i n g Y o u r S u c c e s s. Designing Charge Pump Based Converters. JUN 2011. CHARGE PUMPS. Advantages No coils! Low EMI (if well designed)

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JUN 2011

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  1. P o w e r i n g Y o u r S u c c e s s Designing Charge Pump Based Converters JUN 2011

  2. P o w e r i n g Y o u r S u c c e s s Designing Charge Pump Based Converters JUN 2011

  3. CHARGE PUMPS Advantages No coils! Low EMI (if well designed) Fully integrated (if you only need a few 1uA) Digital control (when regulation is needed) Disadvantages Lower efficiency (if you need to regulate the output voltage) More switches and more silicon area Large inrush currents (if badly designed) CONFIDENTIAL JUN 2011

  4. CHARGE PUMPS When to use? When you cannot use coils Extra silicon area is not a problem System has long standby periods Pins are available Output current range is medium 10 mA – 1 A* Or Fully integrated Small currents <100 uA CONFIDENTIAL JUN 2011

  5. 3x III III 2x 2x 1.5x II 1x I 1x 1x I 1/2 CHARGE PUMPS Conversion topology tradeoffs: CP vs DC/DC vsLDO Component Added pins Area [mm2] for 600mA 0.4 0.6 0.55 0.65 0.85 0.7 0.3 0.75 Vout > Vin 3x 3x III III III III 2x 2x 2x 2x Vout = Vin 1.5x 1.5x II II 1x 1x 3x Vout < Vin I I 1x 1x 1x 1x I I 1/2 1/2 LDO DC/DC DC/DC DC/DC CP /2 CP 2x CP 3x CP /3 Buck Boost H - Bridge CONFIDENTIAL JUN 2011

  6. CHARGE PUMPS Conversion topology tradeoffs: CP vs DC/DC vsLDO CONFIDENTIAL JUN 2011

  7. CHARGE PUMPS In principle Easy to understand Simple to design Very quick to develop At the end As complex as any engineer might like  (www.sii.co.jp) CONFIDENTIAL JUN 2011

  8. CHARGE PUMPS In principle S1 Iout S4 - + S3 Vcx=Vin CX Vin Vout S2 S1 Iout S4 - + S3 Vout=Vcx+Vin==2.Vin CX Vin Vout S2 CONFIDENTIAL JUN 2011

  9. CHARGE PUMPS Ideally Fixed voltage gain (G= 1/3, ½, 2/3, 1x, 2x, 3x) In reality Looses so output voltage drops with load CONFIDENTIAL JUN 2011

  10. CHARGE PUMPS Ideally No voltage control In reality Voltage control is required (usually a system requirement and also pulse skipping reduces switching losses at light loads) CONFIDENTIAL JUN 2011

  11. CP PROB & SOL Pulse skipping control Need regulation Slow turn-on switches High quiescent current Current limited switches Incomplete charging with digital control High ripple High inrush current Over current comparator Large Vi range Multi-mode digital control Avoid PMOS body diodes turn on Noise CONFIDENTIAL JUN 2011

  12. NEED REGULATION Pulse skipping as simple as it gets  If you use this simple version you will probably get large ripple output!! CONFIDENTIAL JUN 2011

  13. HIGH RIPPLE As bad as it gets at full charge/discharge with regulation  Might be or Might be CONFIDENTIAL JUN 2011

  14. HIGH RIPPLE Inductive dominated ripple Slow turn-on switches Resistive dominated ripple Current limited switches OR Incomplete charging CONFIDENTIAL JUN 2011

  15. SLOW TURN-ON SW Good solution for inductive dominated ripple and EMI reduction Simple but effective slow turn-on switch (do not use ideal current sources) CONFIDENTIAL JUN 2011

  16. CURRENT LIMITED SW Good solution for resistive dominated ripple and current limitation Stability needs to be checked with bond wire and capacitor parasitic Improves incomplete charging digital control (better solution than using Rdson or additional resistors to limit charging current) CONFIDENTIAL JUN 2011

  17. INCOMPLETE CHARGING With digital control Simple Effective Lower ripple Maintains fast response to load transients Requires larger flying capacitor Requires some type of current limitation: Rdson; additional R; current limited switches CONFIDENTIAL JUN 2011

  18. INCOMPLETE CHARGING Digital control of flying capacitor states and R limited charging/discharging Vo is low n Idle y Discharge to Vo Vo is low n y Charge from Vi Resulting ripple CONFIDENTIAL JUN 2011

  19. INCOMPLETE CHARGING Bad load balancing (CP with two flying capacitors) Unbalanced capacitor charge Simple solution: use complete charging on the flying capacitors and limit the discharge current for partial discharges CONFIDENTIAL JUN 2011

  20. INCOMPLETE CHARGING Improved control with limited discharge current Vo is low n y Incomplete discharge to Vo Complete charge from Vi Resulting ripple CONFIDENTIAL JUN 2011

  21. INCOMPLETE CHARGING Improved control with limited discharge current Min period is 2 pulses (1 charge pulse + 1 discharge pulses) Plus the effects of Limit Cycle Oscillations CONFIDENTIAL JUN 2011

  22. INCOMPLETE CHARGING Limit Cycle Oscillations Vo Same as for any other pulse skipping control… CONFIDENTIAL JUN 2011

  23. INCOMPLETE CHARGING Limit Cycle Oscillations CONFIDENTIAL JUN 2011

  24. HIGH INRUSH CURRENT Current limited switches or Over current comparator S1 Iout S4 - + S3 CX Vin Vout S2 CONFIDENTIAL JUN 2011

  25. LARGE VI RANGE Multimode auto switching Lots of modes and conditions but simple digital implementation CONFIDENTIAL JUN 2011

  26. NOISE Avoid turn on of parasitic diodes Vout CXP AGND S4 CXP P+ P+ P+ N+ N+ P+ S1 NW Iout S4 - + S3 CX Vin Vout S2 PSUB CONFIDENTIAL JUN 2011

  27. FRAC CP EXAMPLE 9 sw multimode topology CX1 CX2 S9 S1 S2 S3 S4 S5 S6 S7 S8 Iout Vout Vin cpi cp2a cp1b pgnd cpo cp1a cp2b Gains: 1/3; ½; 2/3; 1 CONFIDENTIAL JUN 2011

  28. FRAC CP EXAMPLE Layout Fractionary CP 10 Aconsumption CONFIDENTIAL JUN 2011

  29. P o w e r i n g Y o u r S u c c e s s CONFIDENTIAL JUN 2011

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