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

CONFIDENTIALJUN 2011 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) CHARGE PUMPS

CONFIDENTIALJUN 2011 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 CHARGE PUMPS

CONFIDENTIAL CHARGE PUMPS DC/DC Conversion topology tradeoffs: CP vs DC/DC vs LDO LDODC/DC BoostH-Bridge CP 2xCP 3xCP /2 Vout<Vin 1/2 1x 2x 1x 2x 1.5x 3x I II III I Vout > Vin Vout = Vin Added pins Component Area [mm 2 ] for 600mA DC/DC Buck 0.3 1/2 1x 1/2 1x 2x 1x 2x 1x 2x 1.5x 3x 1x 2x 1.5x 3x I II III I II III II 3x 0.7 CP /3 JUN 2011

CONFIDENTIAL CHARGE PUMPS Conversion topology tradeoffs: CP vs DC/DC vs LDO JUN 2011

In principle Easy to understand Simple to design Very quick to develop At the end As complex as any engineer might like CONFIDENTIAL CHARGE PUMPS ( JUN 2011

In principle CONFIDENTIAL CHARGE PUMPS S1S1 V in I out V out S2S2 S3S3 S4S4 CXCX V cx =V in +- S1S1 V in I out V out S2S2 S3S3 S4S4 CXCX +- V out =V cx +V in = =2.V in JUN 2011

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

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 CHARGE PUMPS JUN 2011

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

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

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

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

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

Good solution for resistive dominated ripple and current limitation CONFIDENTIAL CURRENT LIMITED SW 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) JUN 2011

CONFIDENTIAL 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 JUN 2011

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

CONFIDENTIAL 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 JUN 2011

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

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

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

CONFIDENTIAL INCOMPLETE CHARGING Limit Cycle Oscillations JUN 2011

CONFIDENTIAL HIGH INRUSH CURRENT Current limited switches or Over current comparator JUN 2011 V in I out V out S2S2 S3S3 S4S4 CXCX +- S1S1

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

CONFIDENTIAL NOISE Avoid turn on of parasitic diodes JUN 2011 PSUB AGND N+ CXP N+ S4 NW P+ V out P+ V in I out V out S2S2 S3S3 S4S4 CXCX +- S1S1 C XP

CONFIDENTIAL FRAC CP EXAMPLE 9 sw multimode topology JUN 2011 V in S1S1 I out S2S2 S3S3 S4S4 S5S5 S6S6 S7S7 S8S8 Gains: 1/3; ½; 2/3; 1 S9S9 C X1 C X2 V out cpicp1bcp2apgnd cp1a cpo cp2b

CONFIDENTIAL FRAC CP EXAMPLE Layout JUN 2011 Fractionary CP 10  A consumption

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