Linear Technology Corporation Power Seminar LDO 2016. 10. 12. LTC Korea 영업강전도부장 010-8168-6852 jdkang@linear.com 기술박종만차장 010-2390-2843 jmpark@linear.com
LDO 목차 1) LDO feedback 동작원리, 2) LDO 종류 3) LDO 특성 4) LDO 효율및발열 - 반도체발열특성 5) LDO Summary 6) Special LDO 2
1. LDO Copyright 2014 Linear Technology. All rights reserved.
Voltage Regulator Solutions Linear Regulator Simple to design and use! Low noise Low efficiency Heat problems Switching Regulator (Inductor based) High efficiency (can be over 95%!) Small Requires inductor Switching noise Switching Regulator (Charge-Pump) Better efficiency than LDOs Small, simple solution Limited voltage and current options Linear Technology offers high performance solutions for all three styles 4
LDO 의 Feedback 동작원리 5
Regulator feedback Vin Vin voltage drop 1.Load current 가작다면 R1,R2 높은저항값사용가능 2.Load current 가변화가없다면 Vcc 는일정한전압을가짐 3.Vin 전압변화가없다면 Vcc 는일정한전압을가짐 1.Load current 증가할수록고정된 R1 저항을바꿀수없으므로 Vcc 전압낮아짐. 2. 만약높은전류가필요하다면 R1 저항값을낮춰야하지만그경우 Source impedance(rin) 에의해입력전압이낮아짐. 6
Regulator 의 feedback Load 3.3V clamping 1.R1 저항에 diode clamping current 이하로전류 setting 2. Diode clamping current 이하의변하지않는 load 에사용 3. 출력전류의변화에는 clamping current 에서대응가능 4. 온도에따른 Regulation 오차가큼 7
Regulator 의 feedback Vcc =3.3V Load 4V clamping 1.R1 저항에 diode clamping current 는 NPN 의 base 전류 setting 2. Q1 의증폭도및 R2 저항에의해 load 전류증가시대응가능 3. Load 변화에정밀한 Regulation 불가능하나출력 regulation 요구사항이많지않은경우사용가능. 8
Regulator 의 feedback 다양한조건에서안정적인 Regulation 을위해입력전압 / 출력전압 / 출력전류에따른저항값을변경해줄수있는 feedback loop 필요. 9
Linear Regulator 의동작영역 BJT or FET FET Dynamic Range Linear Region Saturation Region BJT Dynamic Range Linear Regulator 는 Transistor(or FET) 가 Linear 영역에서동작 Switching Regulator 는 Transistor(or FET) 가전영역에서동작 10
Regulator 의 Feedback 동작 Iin = Iout Ground current PNP ADJ pin NPN Feedback 동작원리 출력전류의증가 -> Vout 전압감소 -> ADJ pin 전압감소 -> OP amp 출력 High -> NPN TR on -> PNP base 전류증가 (Ground current) -> 증폭도에의해출력에전류공급 -> Vout 전압다시증가 11
Linear Regulator 종류 12
Various LDO type 13
BIPOLAR VS CMOS PASS DEVICE Bipolar Pass Device Advantages Allows very low (down to 1V) or very high (up to 80V) Wide VIN operation. Faster transient response due to higher gm. CMOS Pass Device Advantages Dropout voltage is linear with output current and decreases to zero at no load. No additional VIN or GND pin DC current to drive CMOS gate.
NPN/NMOS VS PNP/PMOS PASS DEVICE NPN/NMOS Pass Device Higher bandwidth and faster transient response. Higher frequency power supply rejection ratio (PSRR). Higher dropout voltage in single supply operation. Requires dual supply operation for equivalent dropout voltage performance as PNP/PMOS. PNP/PMOS Device. Low dropout voltage performance with single supply operation. Easier to provide reverse battery, reverse output protection and reverse input-to-output protection with PNP. Note the feedback loop s extra inversion compared with the NPN/NMOS loop.
LDO 의특성 16
What is dropout? 17
Linear Regulator Standard NPN Regulator Darlington 구조로출력전류최대사용가능. But Dropout voltage 증가 Minimum Dropout Voltage = 출력전압을 regulation 하기위한입력전압과출력전압의최소차이 Linear Regulator Minimum Dropout Voltage = > 1 V 18
Linear Regulator Load Current Dropout voltage 19
Various Dropout 20
LDO(Low dropout) Regulator PNP Transistor or CMOS Minimum Dropout Voltage = can be 300mV 고정전압제품의경우저항이내장되어있음 21
VLDO(Very Low dropout) Bipolar LDO : 300mV@150mA CMOS LDO : 100mV@150mA VLDO 50mV@ 300mA 22
LDO specification (LT1761 example) 23
LT1761 Low Noise LDO 24
Dropout vs Load Load Current Dropout voltage 25
Dropout vs temp. Dropout voltage increased by load current & temperature 26
Line/Load regulation/transient response 27
GND/SHDN pin current Load 증가시 GND current 증가 ( base current 이기때문 ) 28
LDO output Noise Vin DC/DC ripple vs Vout LDO ripple Power Supply Rejection Ratio 29
Power Supply Ripple Rejection Ratio 30
LDO output Noise Low Noise LDO = ~ 20uVrms VLDO = ~100uVrms Noise 특성은 resistor thermal noise, TR flicker noise LDO 자체의특성임. 입력전압의 range 에는관계없음. Switching regulator > 10mV 다만 Dropout Mode 로동작시입력 Ripple 전압, 출력으로그대로보냄. 31
LDO 의효율및발열 32
IC 의동작온도 IC 의 package 및조건에따른동작온도는 Datasheet 의 Operating Junction Temp range 보다는낮아야함. 온도가넘을경우 IC damage 또는성능 Degrade 가나타남. 33
TJ / TC / TA 34
열전달과정 35
반도체온도상승예측 36
반도체온도상승예측 LTC Linear Charger 의 Thermal performance 개선 37
반도체온도상승예측 Pd (Power loss) 를계산한다 (Pd = Pin Pout, Inductor loss, Diode loss고려 ) TRISE = Pd x Rth j-a Rth j-a = Rth (junction-case + case-heatsink + heatsink-amb) Package 가결정, SMD/ 히트싱크부착히트싱크면적에따라 ( 고정값 ) ( 거의무시가능 ) (Graph 참조 ) 실제측정될온도 = Trise + Tamb 이온도는 die 온도를계산한것으로실제 Package 온도는 die 온도보다낮음 계산한온도는 IC 의 operating temperature 보다낮아야 IC 사용가능!! 38
LDO 효율및발열계산 %Efficiency = Power Out Power In x 100 = I OUT (V OUT ) (I IN +I GND )V IN x 100 I IN I OUT V IN V OUT I GND IGND= 무시가능 즉, 입출력전압비가효율임 39
Device 온도계산 - LDO 12V -> 3.3V@1A 일경우 Pd (Power Loss) = (Vin Vout) X Iout = (12-3.3)V X 1A = 8.7W TRISE = Pd x Rth j-a = 8.7W X 35 C/W = 304C!! 외부환경온도 75C 일경우 Die 온도 = 75C + 304C = 379C 사용불가!! 40
Device 온도계산 - Switching regulator 12V -> 3.3V@1A 일경우 출력 Watt = 3.3V X 1A = 3.3W 여기서효율 90% 입력 Watt = 3.3W X 100/90 = 3.66W Power loss = = 3.66W - 3.3W = 0.36W TRISE = Pd x Rth j-a = 0.36W X 40 C/W = 14.4C!! 외부환경온도 75C 일경우 Die 온도 = 75C + 14.4C = 89.4C 사용가능!! 41
LDO vs Switching regulator Linear regulator 변환효율 - Vin= 7V Vout = 3.3V 일때 47% - Vin=12V Vout = 3.3V일때 27% - Vin=12V Vout = 1.2V일때 13% LDO는효율저하로발열문제및 Battery 사용시간단축문제를안고있음 효율 80% 이상 Switching Regulator 사용시 스위칭 Loss 에의한효율저하 42
Special LDO 43
LT308x series Vout down to 0V 44
LT308x series parallel output 45
LT304x Very low noise LDO 46
LDO vs Switching regulator Benefits: Why Charge Pump Circuits? 1. Simple & Low cost 2. Low noise/low ripple/low EMI 3. Fast Transient response 4. Low dropout with high efficiency Penalties (compared to inductor-based PWM solutions) : 1. Low efficiency at Low duty and Heat problem 47
감사합니다. 영업지원 : 강전도 (jdkang@linear.com / 010-8168-6852) 기술지원 : 박종만 (jmpark@linear.com / 010-2390-2843)