LDO DCDC Charge Pump的原理比较与不同之处.ppt

1、Voltage regulator,Simcom Hardware Dept.2,wangtao,Agenda,Voltage regulator presentation: AC-AC DC-AC DC-DC,Agenda,DC-DC Voltage regulator presentation: LDO Charge pump (inductor less DC-DC) DC-DC (inductor),LDO,LDO ( Low Dropout) LDO is a linear regulator Dropout voltage output voltage within 100mV,

2、(Vin Vout) min,LDO,LDO,Working principle:,The voltage divided by resistors R1 PD is limited by package. Compare with step down buck DC-DC, for higher power dissipation or requirements for higher efficiency, recommend buck. Capacitor Requirements The output capacitor and especially Equivalent Series

3、Resistance (ESR) are critical for stability. Noise and PSRR Select an LDO with high power supply rejection ratio (PSRR) for noise immunity from the input supply and low output noise. Some LDO have a bypass (BP) pin for adding capacitance to lower the output noise.,LDO parameters,Ceramic Capacitor Eq

4、uivalent Circuit Equivalent Series Resistance (ESR) is a critical factor in circuit performance Capacitor Impedance is a function of: Cap Value, ESR and Frequency,LDO parameters,Things to know about Ceramic Caps:,ESR is a function of: Physical size Larger case size caps have lower ESR Material Type

5、X7R Best (lowest ESR) X5R Good Y5V Low cost (highest ESR) Capacitance vs. Frequency: Capacitance value becomes smaller as frequency increases (impedance drops) Again material type has an effect,LDO parameters,X7R Material MLCC Lower ESR Lower impedance Better Capacitance vs. Frequency Good Temp. Tol

6、erance (+/- 10%),Y5V Material MLCC Higher ESR Higher impedance Poor Capacitance vs. Frequency Poor Temp. Tolerance (+20/- 80%),LDO selection: LOW noise, HIGH PSR No enough PCB area (inductor less) Low voltage drop Low cost,Regulator Overview,Charge Pump,Types of Charge Pump Devices: Types of Charge

7、pump devices are available in different topologies: Voltage Doubling (2X) Charge Pumps Vout = 2 x Vin Fractional Charge Pumps Vout = N x Vin, where N = device multiplication Example: Vout = 1.5 x Vin Regulated Output Charge Pumps Can be 2x, 3x, Fractional, etc.,Voltage Double Charge Pump,Working pri

8、nciple:,Voltage double charge pump block diagram (Vout = 2 x Vin),Charge Pump Phase Cycle 1: Charge CFLY,Charge Pump Phase Cycle 2: Bootstrap CFLY to the Output,Voltage Double Charge Pump,Equivalent Circuit for Phase Cycle 1:,Equivalent Circuit for Phase Cycle 2:,Fractional Charge Pump,Working princ

9、iple:,Fractional Charge Pumps: Fractional charge pumps offer a technique to multiply an input voltage by a non-integer multiplication factor Fractional charge pumps can have efficiency advantages in low output voltage applications,Equivalent Circuit for Phase Cycle 1:,Equivalent Circuit for Phase Cy

10、cle 2:,Fraction Charge Pump Works: Operates with 2 switching cycle phases (same as a voltage doubling charge pump) Two “Flying” capacitors are used: In the first switching cycle CFLY1 and CFLY2 are connected in series and placed across Vin, which effects a voltage divider at Vc = Vin/2 for each “Fly

11、” capacitor. In the second switching cycle CFLY1 and CFLY2 are connected in parallel, then switched to be in series between Vin and Vout. Vout = Vin + Vin/2 = 1.5 x Vin,Fractional Charge Pump,Regulated Charge Pump,Working principle:,Regulated Charge Pumps: Regulated charge pumps are voltage doubling

12、, tripling or fractional charge pumps with an output voltage regulation system and feedback control. Regulated charge pumps can provide a stable output voltage from a varied input supply, which is ideal for battery operated devices.,Charge Pump Efficiency,Primary items which effect efficiency: RDS(O

13、N) of the MOSFET switching devices I2R Loss Lower RDS specs are better Operating quiescent current Vin versus Vout for a given charge pump topology -This applies to regulated charge pumps Types of external capacitors used -Cin, Cout and Cfly,Charge Pump Efficiency,Efficiency of Regulated Charge Pump

14、s: Regulated Voltage Doubling Charge Pumps Fixed output voltage level Input voltage may vary with in the device operating range The input voltage is doubled, then regulated down to the desired output voltage. Theoretical Efficiency = = VOUT / 2VIN Example: VIN = 2.8V, VOUT = 3.3V, = 58.9% Example: V

15、IN = 3V, VOUT = 4.5V, = 75%,Charge Pump Efficiency,Efficiency of Fractional Charge Pumps: Regulated Fractional Charge Pumps Fixed output voltage level Input voltage may vary with in the device operating range Fractional charge pumps have an advantage in low voltage applications since the Input to Ou

16、tput difference voltage to be regulated is small. Theoretical Efficiency = = VOUT / 1.5VIN Example: VIN = 2.8V, VOUT = 3.3V, = 78.6% Example: VIN = 3V, VOUT = 4.5V, 100%,External component selection,External Component Selection: Charge pump devices typically require 3 to 4 external capacitors depend

17、ing upon circuit topology. The CIN/COUT to CFLY ratio can range from 1:1 to 10:1 Capacitor value and properties are critical to good charge pump performance Important Capacitor Characteristics: Capacitor value Dielectric material type Physical size Capacitor equivalent series resistance (ESR),Capaci

18、tor selection: Ceramic Capacitors are typically the best choice Ceramic capacitors are non-polarized and have low ESR characteristics, typically 100m Ceramic Capacitor ESR: Capacitor ESR has a dramatic effect on output ripple ESR can vary depending capacitor type, value and case size. X7R Dielectric

19、 is the best (higher cost) X5R Dielectric is good Y5V Dielectric is poor (lower cost) Tantalum and Aluminum Electrolytic Capacitors These types of capacitors may be used with charge pumps for Cin and Cout at the expense of performance Both have high ESR characteristics Output ripple and efficiency w

20、ill be compromised CFLY must be a non-polarized capacitor (bi-directional current flow),External component selection,Charge pump output ripple,Output Ripple Characteristics: Output ripple is significantly effected by the external capacitor value. The following plots are examples measured with an AAT

21、3111 showing how capacitor value can effect output ripple. AAT3111: VIN = 3.0V, VOUT = 5.0V, ILOAD = 50mA,0805 Size, X7R Ceramic CIN = COUT = 2.2uF CFLY = 0.22uF Vripple = 60mVp-p,0805 Size, X7R Ceramic CIN = COUT = 4.7uF CFLY = 0.47uF Vripple = 45mVp-p,0805 Size, X7R Ceramic CIN = COUT = 10uF CFLY

22、= 1uF Vripple = 30mVp-p,Charge pump output ripple,Output Ripple Characteristics: Output ripple is significantly effected by the external capacitor material type. The following examples were measured with an AAT3110 showing how equal value and size capacitors of different material types can effect ou

23、tput ripple. AAT3110: VIN = 3.0V, VOUT = 5.0V, ILOAD = 50mA,0805 Size, Y5V Ceramic CIN = COUT = 10uF CFLY = 1uF Vripple = 90mVp-p !,0805 Size, X7R Ceramic CIN = COUT = 10uF CFLY = 1uF Vripple = 35mVp-p,DC-DC,three basic switching topologies in common Types of DC-DC devices are available in three top

24、ologies: BUCK Step-down power stage. Power supply designers choose the buck power stage. the required output voltage is always lower than the input voltage BOOST step-up power stage. Power supply designers choose the boost power stage. the required output voltage is always higher than the input volt

25、age BUCK/BOOST step-up/down power stage. Power supply designers choose the buck-boost power stage. the output voltage is inverted from the input voltage, and the output voltage can be either higher or lower than the input voltage.,Step Down “Buck” Converter,Step UP “Boost” Converter,Step Up / Step D

26、own “Buck - Boost” Converter,DC-DC,DC-DC,PWM Control Signal Details DC steady state assumes VOUT and VIN are constant Steady state dictates that the average inductor voltage must be zero (volt-sec balance) The inductor DC current is equal to the load currentno DC current into the output cap constant

27、 output voltage,DC-DC,Basic Step-Down “Buck” DC/DC Converter Simple Control 80-90 % efficiency at full load Switching frequency 30kHz -4 MHz Light load efficiency improvement with burst mode, frequency shift or pulse skipping,DC-DC,PWM Switching Control: Output Voltage is the average of the voltage

28、applied to the output LC filter,DC-DC,Synchronous Step-Down DC/DC Conversion More efficient than a conventional Buck converter Eliminates the external Schotky Diode Required “dead-time” break before make switching to limit shoot-thru current and improve efficiency Made possible by use of CMOS proces

29、s technology Light Load Efficiency Improvements Pulse skipping or Burst Mode at light load to reduce switching losses,Control Mosfet,Synchronous Mosfet,DC-DC,Synchronous Switching “Dead-Time” What is it? Time when both control and synchronous switches are off Advantage Eliminates Mosfet shoot-thru c

30、urrent and associated losses Reduces switching losses associated with the turn on of the synchronous switch (VDS is zero when VGS is applied) Disadvantage Diode body losses are greater than Mosfet RDS(ON) losses for the same current during the dead time. Solution Design synchronous converters with g

31、ood break-before-switching Use a very high switching frequency Sub-micron CMOS and BCD process allow the solution to be possible,DC-DC,Synchronous Switching States,DC-DC,Soft-Start is Very Important Switchers Reduces In-rush currents during start-up Limits supply rail voltage sag at start-up,Soft-St

32、art switcher turn-on response,Switcher turn-on response without soft-start,DC-DC,Typical IOUT Current Limit Response,ILIMIT at 1.3A for VOUT = 1.5V,ILIMIT at 1.2A for VOUT = 3.3V,DC-DC,High vs Low Switching Frequency High switching frequencies: Typical switching frequencies above 800kHz Allow for th

33、e use of small external components Output inductors and capacitors Permit the use of switching converters in RF applications High switching frequencies are less likely to interfere with baseband systems Good Transient response Lower switching ripple Low switching frequencies: Typical switching frequ

34、encies from 20kHz to 800kHz Poor transient response Large external components High switching ripple and noise Low cost / performance switching converts,External component selection,External Component Selection: Good performance is dependant upon the right external component selection Output Capacito

35、rs Ceramic Capacitors Applies to both Switching and Linear (LDO) Regulators Output Inductor Inductors Wire Wound Multilayer Chip Diode,External component selection,Capacitor selection: The Capacitor should be low ESR Minimized switching noise and ripple For best transient response Different Material Types Effect performance X7R, X5R and Y5V are most common One must balance circuit performance vs. size and cost limitations,External component selection,Inductor selection: The inductor should be low ESR For best power conversion efficiency Minimized switching noise and ripple Lo