power management
TRANSCRIPT
Power Management Systems, System on Chip (SoC)
Power Management Systems, System on Chip (SoC)
Jyotirmoy GhoshJyotirmoy GhoshAdvanced VLSI Design Laboratory,Advanced VLSI Design Laboratory,Indian Institute of Technology KharagpurIndian Institute of Technology KharagpurEmailEmail-- [email protected]@iitkgp.ac.in
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ContentsWhat is power managementHow to decideDC-DC power converters■ LDO■ Inductor based switched mode converters
● Closed loop control■ Switched capacitor converters
Voltage regulator module■ Dynamic voltage scaling■ Current mode control■ Pulse skip mode
SOC implementation
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What is Power Management ?
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A direct connection is not desirable.
Supply LoadVin VoutL, C, Power switches, etc.
Converter - Power Stage
Controller
An Example of a Power Management System: DC-DC Converter
2.5V-5.5V 1.2V
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Domains of Power Management
4
DC to DC – Cell phones
DC to AC – Home inverter
AC to DC – Rectifier as in a PC supply
AC to AC - Transformer
Voltage Conversion
OthersBattery Charging – Cell phone chargers
Drivers – CFL and LED Drivers
Power Quality Improvement
And many more…
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Typical applications
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World wide Power Management
The market is expected to grow at a rate higher than most of other areas in IC design.
In many large analog companies, half of the business is in power management.
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Example: Power Management Unit for a Notebook
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How to choose?Input - Output Voltage RangeLoad current Voltage and Current RippleEfficiencyNature of ApplicationTransient RequirementsLoop BWEMIInput – Output IsolationBoard AreaCost…
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DC-DC conversion techniques
9
Low Drop-Out Regulators
Inductor Based Switched Mode Power Converter
Switched Capacitor Converters
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Low Drop-Out Regulator
10
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Resistor divider
11
VinR2
R1 Vout
LOA
D
→ V’out
Can’t draw any current without causing extra drop!
inout VRR
RV21
1
+=
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LDO – Low Drop Out regulator
12
The idea is to control R1.
VinR2
R1
Vout
Drop R2.
LOA
D
→V’out
Use feedback control to adjust the value of R1.
Controller
→ Vout
Consider Vin = 5.0 V; Vout = 1.0 V. Efficiency = ?
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R1 to a MOSFET
13
Power MOSFET
Vin
(Acting as R1)
Vout
LOA
DController
→ Vout
Driver
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Inductor Based Switched Mode Converter
14
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Step down switching converter: Buck Converter
Buck Converter Circuit
Inductor Voltage
ON-state OFF-state
Ts
L0
DTs Ts
L L0 DTs
1 V dt 0Ts
V dt V dt 0.
(Vg Vo)DTs ( Vo)(1 D)Ts 0 Vo DVg
=
⇒ + =
⇒ − + − − =⇒ =
∫
∫ ∫
Applying volt-sec balance for the inductor:
VoDVg
=Conversion ratio of Buck Converter:Thus, this is a step-down conversion
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Analysis of Buck Converter Cont..Inductor current ripple:
L
O
diInductor voltage current relation: V Ldt
During time interval dt D.Ts, change in inductor current di is i ;and voltage across the inductor is (Vg V )
=
=∆
−
OL
OL
OL O
(Vg V )DTsThus iL
(1 D)V Tsor, iL
VSince I IR
−∆ =
−∆ =
= =
L
L
i (1 D)RTsCurrent ripple factor I L∆ −
=
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Analysis of Buck Converter Cont..
Output voltage ripple:Total charge transferred to capacitor that causes the voltage to swing from maximum to minimum:
2
Voltage ripple factor Vo (1 D)Ts
Vo 8LC∆ −
=
8LCD)T(1V
8CT∆i
C∆q∆V
8T∆i
2T
2∆i
21∆q
2SOSL
O
SLSL
−===
==
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Inductor Voltage
From inductor volt-sec balance:
D)(1VgVor,
0D)Ts)(1V(Vg(Vg)DTs
O
O
−=
=−−+
D11
VgVO
−=
Boost Converter Circuit ON-state OFF-state
Conversion ratio of Boost Converter:
Thus, this is a step-up conversion
Analysis of Boost Converter
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Analysis of Boost Converter Cont..Inductor current ripple:
diInductor voltage current relation: V=L
dt
During tiem interval dt= D.Ts
change in inductor current di is iL
and votlage across the inductor is Vg
∆
L
L 2
VgDTsThus, iL
Io Vo VgI(1 D) R(1 D) R(1 D)
∆ =
= = =− − −
L
L
2D.(1 D) RTsiCurrent ripple factor
I L
−∆=
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Analysis of Boost Converter Cont..Output voltage ripple:Total charge transferred to capacitor that causes the voltage to swing from maximum to minimum:
O s
O s OO
q I DT
I DT V DTsqThus, VC C RC
∆ =
∆∆ = = =
O
O
V DTsVoltage ripple factor V RC∆
=
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Cascading of Buck Converter and Boost Converter
Voltage conversion ratio:D1
DVgVO
−= when, Vg)(VO ≥ )5.0( ≥D
when, Vg)(VO < )5.0( <D
Non inverting Buck-Boost Converter
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Switched Mode Converter in Closed Loop
22
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Classical PWM Voltage mode control
23
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Small signal model
24
T(s) = Gvd(s) . H(s) . Gc(s) . 1/VM
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Switched Capacitor Converter
25
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Step-up Conversion
Simple voltage doubler circuit
DDout
DDDDout
V2V or,CV)CV(V
:balance charge-capacitor From
==−
Voltage multiplier circuit – Dickson charge pump
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Step-down Conversion
2IN
OUTVV =
3IN
OUTVV =
On-chip scalable voltage generationGood choice for very low power battery operated systemVoltage scaling below 1V
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Comparison of three classes
Criteria LDO Inductor Based Switcher
Charge Pumps
Voltage Conversion Range
Only Buck1 All (buck, boost, inversion)
All (in discrete steps)2
Efficiency Low High High
Max Output Current Moderate3 High3 Low4
Vout ripple Negligible High High
Design Complexity Moderate High High
This is a basic comparison for typical members from each class and is only meant to give a rough idea. Depending on actual circumstances, exceptions may arise.
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An application of Switching Converter:Voltage Regulator Module (VRM) for Processors
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Technology Challenges
Stringent transient specifications
Low voltage and current ripple
Tight line and load regulations
High efficiency throughout the operation periods
Typical load transient waveform
Typical efficiency vs. load current waveform
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Dynamic voltage scaling
Typical processor voltage and dynamically scaled processor voltage
LEAK2CC P CV losspower CPU += f
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LOAD
DriverDeadband
Latch
PWM Comparator
Vref
Vf
Ve
PID
EA
Vout
Ri
IL
Faster dynamic response
Better stability
Better line regulation
PWM Current Mode Converter
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Difference between VMC and CMC
EAPWM
d
ramp
Vref
V0
Voltage Mode Control
vcontrol
EAComp.
SVref
V0
vcontrol
Rclk
Qd
iL(t)
Current Mode Control
vcontrol
t
Inductor current
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Low load efficiency
Pulse skip mode
Boost converter with pulse skip mode
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SOC Implementation
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Block diagram of buck converter & its different flavors
LOAD
DriverDeadband
LatchPWM Comp
Ramp Osc.
VREF
Error Amp
Compensator
Controller ICConverter IC Fully
Integrated Converter IC
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Commercially where we are now?Controller IC: (Commercially most popular)■ As power circuits and compensator are external, it has lot of flexibility to
change the power circuits for various applications, value of L & C etc.■ But, it takes lot of area.
Converter IC: (Commercially moderately popular) ■ As, fixed power circuit are integrated in-side the chip, it can be used for
specific type of applications.■ As, compensator is also integrated, only specific value of L & C should be
connected as off-chip. ■ It takes much lesser area than the previous solution.
Fully integrated converter IC: (Commercially less popular/ mostly in research phase)■ Can be used for very specific applications. ■ It is most area efficient solution.■ But, it has lesser power efficiency due to the limitation of on-chip L & C.
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Selection of switching frequencyAdvantages and Disadvantages of Higher Switching Frequency
Advantages:■ Enable smaller solution size
● Smaller inductor can be used with higher switching frequency to maintain the same current ripple
● Improve dynamic performance because of higher bandwidth of control loop
Disadvantages:■ Increase AC losses
● Gate drive loss● Switching loss● Dead time loss● AC loss of inductor
■ EMI impact
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Selection of MOSFETs
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• For a given die size, N-MOSFET offers low on-resistance and lower gate charge compared to P-MOSFET but requires “bootstrapped” drive circuit
• Tradeoff in selection: power loss, cost and package type (for discrete MOSFETs)• MOSFETs are characterized by its Figure of Merit (FOM) = Qg * RDS(on)
Vertical MOSFETs:High voltage blocking capabilityHigher packing density
Lateral MOSFETs:Lower gate chargeHigher current carrying capacity per unit cross sectional area at low voltageSuitable for low voltage, high current applicationsTerminals are readily available for connection with metal layers: suitable for on-chip implementation of DC-DC converters
Cross-section of vertical MOS
Cross-section of lateral MOS
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Different losses in converter circuit
Conduction loss:■ Losses due to drain-source resistance of big power MOS■ Conduction loss ∞ RDS_on of the power MOS∞ 1/ Die size.
∆+=
12
22 IIDRP outonDScond **_
( ) swinGDGSGateDrive FVCCP **+=
Gate drive loss:■ Losses due to charging/discharging the highly capacitive gate
node of the power MOS.■ Gate driver loss ∞ Gate charge (Qg=Cg*Vin) ∞ Die size.
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Transition loss:■ Losses across the power switch at the edge of transition.■ tr and tf are the rise and fall time of the switch node
respectively.■ Ipm and Ipp are the minimum and maximum peak value of
inductor current.
( )ppfpmrswintran ItItFVP *****. += 50
2
21
inDBDB VCP *=
Drain-bulk capacitive switching loss:■ Losses due to the parasitic drain-bulk capacitance of the
power MOS in the switch node.
Different losses in converter circuit
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Different losses in converter circuit
Dead time loss:■ Losses due to the conduction of body diode of power MOS
during dead-time.■ VF is the diode forward voltage.■ tD_rise and tD_fall are the dead time at rising and falling edge
respectively.( )fallDriseDswoutFDiode ttFIVP __*** +=
rrswinrr QFVP **=
Body diode reverse recovery loss:■ Losses due to reverse recovery in the body diode of the low-
side power MOS .■ Qrr is the reverse recover charge.
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Different losses in converter circuit
Inductor loss:■ Loss due to the DC and AC resistance of the inductor.
12
22 IRIRP acoutdcInductor
∆+= **
12
2IRP ESRESR∆
= *
Capacitor loss:■ Loss due to the ESR of the capacitor.
Controller loss:■ Loss due to the quiescent current consumption in the
controller.
qinController IVP *=
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Trade-off in optimizing different losses
How to fix the size of power MOS in a particular technology?■ Total power loss is minimum at the point where gate driver
loss and conduction loss is equal.■ This sizing maximizes the power efficiency.
Power dissipation (W)
Die size (mm2)
Optimal die size
Total loss
Gate driver loss
Conduction loss
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Packaging issues
Typical value of bond-wire inductance is 1.5 nH – 4.8 nH.
For high speed converter (not necessarily high frequency converter), di/dt=1A/1nS.
So, assuming 2 nH bond-wire inductance, supply bounce is 2 V!
Solution: Use of lead-less package which eliminates the supply bounce.
+ *(di/dt)
-
+
-
Wafer
Package
PVDD
PGND
Vout
RLOAD
L
C
PMOS
NMOS
Gate Driver
LBONDWIRE
*(di/dt)LBONDWIRE
LBONDWIRE
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Example of layout
47
Layout of a 20MHz dc-dc buck converter in a 0.5 µm process.
NMOS
PMOS
Controller
NMOS Driver
PMOS Driver
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20 MHz DC-DC converter developed by IIT-Kharagpur- An example
AVDD PVDD
VFS1
VFS2
VTS1
VTS2
AGND PGND
SW
VFB
VTEST,ANA
VTEST,DIG
+−
CIN
C CBYPASS
L
VIN
VOUT
Typical application circuit
Die photograph
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20 MHz DC-DC converter developed by IIT-Kharagpur- An example
PCB layout Evaluation board
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Acknowledgement
50
Prof. Amit Patra, Department of Electrical Engineering, IIT KharagpurPower Management Group, AVDL
Rakesh Babu
Asif Eqbal
Pradipta Patra
Ashis Maity
Srikanth Pam
Rupam Mukherjee
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Thank You
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Robert W. Erickson and Dragan Maksimovic, “Fundamentals of Power Electronics,” Springer International Edition, 2006.B. Lynch and K. Hesse, “Under the hood of low-voltage dc/dc converters,” in Proc. Power Supply Design Seminar (SEM 1500), 2002.Jens Ejury,“How to Compare the Figure Of Merit (FOM) of MOSFETs,” Infineon Technologies Application Notes.Donald Schelle, Jorge Castorena, “Buck Converter Design Demystified,”Maxim Integrated Products.Everett Rogers, “Understanding Buck-Boost Power Stages in Switch Mode Power Supplies,” Application Report, Texas Instruments.Power Management technique for multimedia mobile phones. , no. 1, April 2006, Available at www.edn.com.J.M. Rivas, D. Jackson, O. Leitermann, A.D. Sagneri, Yehui Han, and D.J. Perreault, .Design Considerations for Very High Frequency dc-dc Converters,. Power Electronics Specialists Conference, 2006. PESC '06. 37th IEEE, pp. 1.11, 18-22 June 2006.
References
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ReferencesMIC2285 Datasheet, Micrel Inc., 8MHz PWM Synchronous Buck Regulator
with LDO Standby Mode, Available at ww.micrel.com/\_PDF/mic2285.pdf.EP5362Q Datasheet, Enpirion, Inc., 600mA Synchronous Buck Regulators with Integrated Inductor, Available at www.enpirion.com.MIC2245 Datasheet, Micrel Inc., 4MHz PWM Synchronous Buck Regulator with LDO Standby Mode, Available at www.micrel.com/PDF/mic2245.pdf.MAX8460 Datasheet, Maxim Inc., 4MHz, 500mA Synchronous Step-Down DC-DC Converters in Thin SOT and TDFN, Available at www.maxim-ic.comTPS623XX Datasheet, Texas Instruments, 500-mA, 3MHz Synchronous Step-Down Converters in chip scale package, Available at www.focus.ti.com/lit/ds/symlink/tps62315.pdf.S. Abedinpour, B. Bakkaloglu, and S. Kiaei, .A Multi-Stage Interleaved Synchronous Buck Converter with Integrated Output Filter in a 0.18/spl mu/ SiGe process,. Solid-State Circuits, 2006 IEEE International Conference Digest of Technical Papers, pp. 1398.1407, Feb. 6-9, 2006.
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ReferencesB.J. Patella, A. Prodic, A. Zirger, and D. Maksimovic, .High-frequency digital PWM controller IC for DC-DC converters,. Power Electronics, IEEE Transactions on, vol. 18, no. 1, pp. 438.446, Jan 2003.Haifei Deng, A.Q. Huang, and Yan Ma, .Design of a monolithic high frequency fast transient buck for portable application,. Power Electronics Specialists Conference, 2004. PESC 04. 2004 IEEE 35th Annual, vol. 6, pp. 4448.4452 Vol.6, 20-25 June 2004.Yeong-Tsair Lin, Wen-Yaw Chung, Dong-Shiu Wu, Hung-Chan Wang, Hung-Yih Lin, and Jiann-Jong Chen, .A monolithic CMOS step-down DC-DC converter,. Circuits and Systems, 2005. 48th Midwest Symposium on, pp. 448.451 Vol. 1, 7-10 Aug. 2005.http://www.national.com/AU/design/courses/253/index.htm?start_file=swx07/01swx07.htm
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