LDO DCDC Charge Pump的原理比較與不同之處

1、 Voltage regulator Simcom Hardware Dept.2 wangtaoAgendaVoltage regulator presentation: AC-AC DC-AC DC-DCAgendaDC-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, (Vin

2、 Vout) minLDOLDOWorking principle:The voltage divided by resistors R1 & R2 is compared with the internal reference voltage by the error amplifierThe MOSFET, which is connected to the Vout pin, is then driven by the subsequent output signal. The output voltage at the Vout pin is controlled &

3、stabilized by a system of negative feedback. LDO parameters Input VoltageThe minimum Vin must be larger than Vout + VDO, independent from the minimum value given in the selection table. EfficiencyBy neglecting the quiescent current (Iq) of the LDO, efficiency can be calculated as Vout/Vin. LDO param

4、eters Power DissipationPD = (Vin Vout) x Iout; PD is limited by package. Compare with step down buck DC-DC, for higher power dissipation or requirements for higher efficiency, recommend buck. Capacitor RequirementsThe output capacitor and especially Equivalent Series Resistance (ESR) are critical fo

5、r stability. Noise and PSRRSelect 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 parametersCeramic Capacitor Equivalent Circuit Equivalent Series

6、Resistance (ESR) is a critical factor in circuit performance Capacitor Impedance is a function of: Cap Value, ESR and FrequencyLDO parametersThings to know about Ceramic Caps:ESR is a function of:Physical size Larger case size caps have lower ESRMaterial TypeX7R Best (lowest ESR)X5R GoodY5V Low cost

7、 (highest ESR)Capacitance vs. Frequency:Capacitance value becomes smaller as frequency increases (impedance drops)Again material type has an effectLDO parametersX7R Material MLCCLower ESRLower impedanceBetter Capacitance vs. FrequencyGood Temp. Tolerance (+/- 10%)Y5V Material MLCCHigher ESRHigher im

8、pedancePoor Capacitance vs. FrequencyPoor Temp. Tolerance (+20/- 80%)LDO selection:LOW noise, HIGH PSRNo enough PCB area (inductor less)Low voltage dropLow costRegulator OverviewCharge PumpTypes of Charge Pump Devices:Types of Charge pump devices are available in different topologies:Voltage Doublin

9、g (2X) Charge Pumps Vout = 2 x VinFractional Charge Pumps Vout = N x Vin, where N = device multiplication Example: Vout = 1.5 x VinRegulated Output Charge Pumps Can be 2x, 3x, Fractional, etc.Voltage Double Charge PumpWorking principle:CONTROL/ CLOCKC+C-VOUTGNDVINSHDNS1S2S3S4CoutCinCflyVoltage doubl

10、e charge pump block diagram (Vout = 2 x Vin)CINCFLYCOUTS1S4S3S2VINVOUT+-+-ICFLYCINVIN+CINCFLYCOUTS1S4S3S2VINVOUT+-+-ICINCFLYCOUTVOUTVIN+-+-+-Charge Pump Phase Cycle 1:Charge CFLYCharge Pump Phase Cycle 2:Bootstrap CFLY to the OutputVoltage Double Charge PumpEquivalent Circuit forPhase Cycle 1:Equiva

11、lent Circuit forPhase Cycle 2:Fractional Charge PumpWorking principle:S1S2S3S4CFLY1CFLY2CINCOUTCONTROL /OSCILLATORVINVOUTENABLEFractional Charge Pumps:Fractional charge pumps offer a technique to multiply an input voltage by a non-integer multiplication factorFractional charge pumps can have efficie

12、ncy advantages in low output voltage applicationsCINCFLY2COUTVOUTVIN+-+-+-CFLY1+-VIN2VINCINCFLY2COUTVOUTVIN+-+-+-CFLY1+-VIN2VINVIN2Equivalent Circuit for Phase Cycle 1:Equivalent Circuit for Phase Cycle 2:Fraction Charge Pump Works:Operates with 2 switching cycle phases (same as a voltage doubling c

13、harge 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” capacitor.In the second switching cycle CFLY1 and CFLY2 are connected in parallel, then switched to be

14、in series between Vin and Vout. Vout = Vin + Vin/2 = 1.5 x VinFractional Charge PumpRegulated Charge PumpWorking principle:CONTROLVREF+-GNDSHDNS1S2S3S4VINCinVOUTCoutC+C-CflyRegulated Charge Pumps:Regulated charge pumps are voltage doubling, tripling or fractional charge pumps with an output voltage

15、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 EfficiencyPrimary items which effect efficiency:RDS(ON) of the MOSFET switching devices-I2R Loss Lower RDS specs are b

16、etterOperating quiescent currentVin versus Vout for a given charge pump topology -This applies to regulated charge pumpsTypes of external capacitors used-Cin, Cout and CflyCharge Pump EfficiencyEfficiency of Regulated Charge Pumps: Regulated Voltage Doubling Charge PumpsFixed output voltage levelInp

17、ut voltage may vary with in the device operating rangeThe input voltage is doubled, then regulated down to the desired output voltage. Theoretical Efficiency = = VOUT / 2VINExample: VIN = 2.8V, VOUT = 3.3V, = 58.9%Example: VIN = 3V, VOUT = 4.5V, = 75%Charge Pump EfficiencyEfficiency of Fractional Ch

18、arge Pumps:Regulated Fractional Charge PumpsFixed output voltage levelInput voltage may vary with in the device operating rangeFractional charge pumps have an advantage in low voltage applications since the Input to Output difference voltage to be regulated is small.Theoretical Efficiency = = VOUT /

19、 1.5VINExample: VIN = 2.8V, VOUT = 3.3V, = 78.6%Example: VIN = 3V, VOUT = 4.5V, 100%External component selectionExternal Component Selection:Charge pump devices typically require 3 to 4 external capacitors depending upon circuit topology.The CIN/COUT to CFLY ratio can range from 1:1 to 10:1Capacitor value a