Current-Mode Adaptively Hysteretic Control for Buck Converters with ...
Current-Mode Adaptively Hysteretic Control for Buck Converters with Fast Transient Response and Improved Output Regulation Kuan-I Wu, Shuo-Hong Hung, Shang-Yu Shieh, Bor-Tsang Hwang, Szu-Yao Hung, and Charlie Chung-Ping Chen
Graduate Institute of Electronics Engineering and Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan Abstract—This paper presents a current-mode adaptively hysteretic control (CMAHC) technique to achieve the fast transient response for DC-DC buck converters. A complementary full range current sensor comprising of chargingpath and discharging-path sensing transistors is proposed to track the inductor current seamlessly. With the proposed current-mode adaptively hysteretic topology, the inductor current is continuously monitored, and the adaptively hysteretic threshold is dynamically adjusted according to the feedback information comes from the output voltage level. Therefore, a fast load-transient response can be achieved. Besides, the output regulation performance is also improved by the proposed dynamic current-scaling circuitry (DCSC). Moreover, the proposed CMAHC topology can be used in a nearly zero RESR design configuration. The prototype fabricated using TSMC 0.25μm CMOS process occupies the area of 1.78mm2 including all bonding pads. Experimental results show that the output voltage ripple is smaller than 30mV over a wide loading current from 0 mA to 500 mA with maximum power conversion efficiency higher than 90%. The recovery time from light to heavy load (100 to 500 mA) is smaller than 5μs.
PVDD Zero-Current Detector
Hys. Comp.
2
L
VOUT
Driver
( Fast Path )
Adaptive Hysteretic Window Generator
Dynamic Current Scaling Circuitry ( Slow Path )
RF1
RESR
RF2
COUT
Ripple Amplifier
RA AL, ωH
Bandgap Reference
RA AH, ωL Soft-Start Circuit
Fig. 1. The proposed current-mode adaptively hysteretic buck converter.
current-mode or type-III compensation in voltage-mode converters, respectively. Both of the design effort and bill of materials (BOM) can be reduced. Therefore, the aforementioned characteristics make the hysteretic converters become one of the most appropriate solutions for applications demand a fast transient response.
INTRODUCTION
As the increasing functionalities in any portable batterydriven device, the power consumption problem has become more serious and emerged as a primary concern. In order to prolong the battery time, a high efficiency power conversion must be accomplished. The switching-mode DC-DC converters have been widely used, because of their excellent performance in power-saving. Among these switching-mode converters, conventional control methods such as voltage-mode, currentmode, and hysteretic topology have been investigated. The current-mode control shows additional advantages of better closed-loop stability, faster dynamic responses, and automatic over-current protection [1]. The comparison of these control methods shows that the converters using hysteretic topology usually have very high slew-rate and amplitude transient. Besides, the hysteretic converters have a simple control architecture that do not require the type-II compensation in
978-1-4799-3432-4/14/$31.00 ©2014 IEEE
Control Circuits & DeadTime Generator
Hys. L
Keywords—Current-mode, adaptively hysteretic, load-transient response, buck converter.
I.
Driver
Hys. H
The organization of this paper is as follows. Section II describes the overall system architecture of the proposed converter. Section III presents the circuit description in detail. The experimental results of the proposed converter are shown in Section IV. Finally, conclusions are made in Section V. II.
PROPOSED CONVERTER ARCHITECTURE
The architecture of the proposed current-mode adaptively hysteretic buck converter is shown in Fig. 1. The rippleamplifier (RA) can magnify the voltage information and isolate the noise from the output node. The adaptive hysteretic window generator (AHWG) will dynamically adjust both of the high and low hysteretic thresholds according to the information sent form RA. Hence, a limited output ripple can
950
M1
Vout
M2 VGP
Voltage & Current
X M3
M4
M8 IB
M9
ILoad
VL
VGN
Vw
Conventional
Rsense
M5
M4
M5
M8
M7
Charging-Path Current Sensor
Fig. 2. The load transient response from light load to heavy load.
M2
M6
MN
time(s)
Load transient response
M1
LX
Vsense
Isense
VH
MP
Y
Power Stage
Fig. 3. Schematic of the charging-path current sensor.
M9 M1
MP
VGP
M2
M15
M3
M16 VH
From Bandgap Bias Circuit
Vsense
X
M3
M4
LX
M11
IB
RF1 VIN
Rsense
M5
M6
M7
M 10
Y
VGN
MN
M7
M8
M9
VL RF2 M17
M10
Adaptive Window Generator & Ripple Amplifier
Power Stage
Fig. 4. Schematic of the proposed discharging-path current sensor.
Fig. 5. Schematic of the ripple amplifier and adaptive window generator.
be obtained. Meanwhile, the dynamic current scaling circuitry (DCSC) will provide a slow path to send the voltage information for further manipulation. A complementary full range current sensor comprising of charging-path and discharging-path sensing transistors is proposed to track the inductor current seamlessly. During the load transient response, the adaptive hysteretic boundary (i.e., VH and VL) will change itself immediately according to the output voltage information. Therefore, the feedback loop will converge much faster than the one with conventional current-mode hysteretic architecture, as shown in Fig. 2. Moreover, the proposed CMAHC topology can be used in a nearly zero RESR design configuration. III.
M14
1 : 1000
Bias Circuit
Discharging-Path Current Sensor
RW
CC
M6 M13
Isense
RC
M12
smaller than that of the power PMOS transistor MP in the power stage. Hence, the current sensing signal Vsense can be obtained efficiently. Although Fig. 3 has the ability of indirect current sensing, it is useless in dealing with the discharging current because the point LX is pulling down to around zero voltage level in this time. As a result, we propose a currentmirror-based discharging-path current sensor, as shown in Fig. 4, to sense the current flowing through the power NMOS transistor MN. At the charging phase, the transistors M9, will pull up the point X to VDD and turn off the transistor M3. At the discharging phase, a matched NMOS transistor M10 will turn on accompany with the power NMOS transistor MN, and tie the point Y down to around zero voltage level. Therefore, a proportional sensing current Isense can be generated and converted to Vsense. With these two complementary current sensors, the full range current information can be obtained.
CIRCUIT IMPLEMENTATION
A. Complementary full range current sensor
B. Adaptively hysteretic window generator
The proposed CMAHC technique needs a full-range current sensor to continuously monitor the inductor current. The most intuitive way is to insert a sensing resistor in series with the inductor [2], however, this method engenders a voltage drop and degrades the conversion efficiency. Fig. 3 shows the structure of the current-mirror-based charging-path current sensor [3], [5]. The negative feedback loop formed by the transistors M3, M4, and M9 will force the points X and Y to become virtual short, and the current sensor is realized by a matched PMOS transistor M1 with the aspect ratio much
The schematic of the adaptive hysteretic window generator (AHWG) and ripple amplifier (RA) is shown in Fig. 5. In the proposed buck converter, two similar RAs have been used. The RA, which is followed by the AHWG, has a larger bandwidth, and therefore a pair of fast response hysteretic thresholds can be obtained. According to the output voltage level, the hysteretic window is adjusted rapidly from this path. This property helps the converter to reduce the reaction time under
951
TABLE I. PERFORMANCE SUMMARY AND COMPARISON
This work
TPE 2007 [4]
JSSC 2004 [5]
TCAS-II 2007 [6]
0.25μm CMOS 4.7 10 3.3 1.8 500KHz-1.5MHz Current-Mode Hysteretic
0.6μm CMOS 4.7 10 3.6 2.5 1.1MHz Current-Mode PWM
0.6μm CMOS 4.7 10 3.6 2.1 500KHz Current-Mode PWM
0.35μm CMOS 4.7 10 3.3 2.0 500KHz Current-Mode PWM
Compensation components
None
CFB=22pF
CC=1nF RZ
Graduate Institute of Electronics Engineering and Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan Abstract—This paper presents a current-mode adaptively hysteretic control (CMAHC) technique to achieve the fast transient response for DC-DC buck converters. A complementary full range current sensor comprising of chargingpath and discharging-path sensing transistors is proposed to track the inductor current seamlessly. With the proposed current-mode adaptively hysteretic topology, the inductor current is continuously monitored, and the adaptively hysteretic threshold is dynamically adjusted according to the feedback information comes from the output voltage level. Therefore, a fast load-transient response can be achieved. Besides, the output regulation performance is also improved by the proposed dynamic current-scaling circuitry (DCSC). Moreover, the proposed CMAHC topology can be used in a nearly zero RESR design configuration. The prototype fabricated using TSMC 0.25μm CMOS process occupies the area of 1.78mm2 including all bonding pads. Experimental results show that the output voltage ripple is smaller than 30mV over a wide loading current from 0 mA to 500 mA with maximum power conversion efficiency higher than 90%. The recovery time from light to heavy load (100 to 500 mA) is smaller than 5μs.
PVDD Zero-Current Detector
Hys. Comp.
2
L
VOUT
Driver
( Fast Path )
Adaptive Hysteretic Window Generator
Dynamic Current Scaling Circuitry ( Slow Path )
RF1
RESR
RF2
COUT
Ripple Amplifier
RA AL, ωH
Bandgap Reference
RA AH, ωL Soft-Start Circuit
Fig. 1. The proposed current-mode adaptively hysteretic buck converter.
current-mode or type-III compensation in voltage-mode converters, respectively. Both of the design effort and bill of materials (BOM) can be reduced. Therefore, the aforementioned characteristics make the hysteretic converters become one of the most appropriate solutions for applications demand a fast transient response.
INTRODUCTION
As the increasing functionalities in any portable batterydriven device, the power consumption problem has become more serious and emerged as a primary concern. In order to prolong the battery time, a high efficiency power conversion must be accomplished. The switching-mode DC-DC converters have been widely used, because of their excellent performance in power-saving. Among these switching-mode converters, conventional control methods such as voltage-mode, currentmode, and hysteretic topology have been investigated. The current-mode control shows additional advantages of better closed-loop stability, faster dynamic responses, and automatic over-current protection [1]. The comparison of these control methods shows that the converters using hysteretic topology usually have very high slew-rate and amplitude transient. Besides, the hysteretic converters have a simple control architecture that do not require the type-II compensation in
978-1-4799-3432-4/14/$31.00 ©2014 IEEE
Control Circuits & DeadTime Generator
Hys. L
Keywords—Current-mode, adaptively hysteretic, load-transient response, buck converter.
I.
Driver
Hys. H
The organization of this paper is as follows. Section II describes the overall system architecture of the proposed converter. Section III presents the circuit description in detail. The experimental results of the proposed converter are shown in Section IV. Finally, conclusions are made in Section V. II.
PROPOSED CONVERTER ARCHITECTURE
The architecture of the proposed current-mode adaptively hysteretic buck converter is shown in Fig. 1. The rippleamplifier (RA) can magnify the voltage information and isolate the noise from the output node. The adaptive hysteretic window generator (AHWG) will dynamically adjust both of the high and low hysteretic thresholds according to the information sent form RA. Hence, a limited output ripple can
950
M1
Vout
M2 VGP
Voltage & Current
X M3
M4
M8 IB
M9
ILoad
VL
VGN
Vw
Conventional
Rsense
M5
M4
M5
M8
M7
Charging-Path Current Sensor
Fig. 2. The load transient response from light load to heavy load.
M2
M6
MN
time(s)
Load transient response
M1
LX
Vsense
Isense
VH
MP
Y
Power Stage
Fig. 3. Schematic of the charging-path current sensor.
M9 M1
MP
VGP
M2
M15
M3
M16 VH
From Bandgap Bias Circuit
Vsense
X
M3
M4
LX
M11
IB
RF1 VIN
Rsense
M5
M6
M7
M 10
Y
VGN
MN
M7
M8
M9
VL RF2 M17
M10
Adaptive Window Generator & Ripple Amplifier
Power Stage
Fig. 4. Schematic of the proposed discharging-path current sensor.
Fig. 5. Schematic of the ripple amplifier and adaptive window generator.
be obtained. Meanwhile, the dynamic current scaling circuitry (DCSC) will provide a slow path to send the voltage information for further manipulation. A complementary full range current sensor comprising of charging-path and discharging-path sensing transistors is proposed to track the inductor current seamlessly. During the load transient response, the adaptive hysteretic boundary (i.e., VH and VL) will change itself immediately according to the output voltage information. Therefore, the feedback loop will converge much faster than the one with conventional current-mode hysteretic architecture, as shown in Fig. 2. Moreover, the proposed CMAHC topology can be used in a nearly zero RESR design configuration. III.
M14
1 : 1000
Bias Circuit
Discharging-Path Current Sensor
RW
CC
M6 M13
Isense
RC
M12
smaller than that of the power PMOS transistor MP in the power stage. Hence, the current sensing signal Vsense can be obtained efficiently. Although Fig. 3 has the ability of indirect current sensing, it is useless in dealing with the discharging current because the point LX is pulling down to around zero voltage level in this time. As a result, we propose a currentmirror-based discharging-path current sensor, as shown in Fig. 4, to sense the current flowing through the power NMOS transistor MN. At the charging phase, the transistors M9, will pull up the point X to VDD and turn off the transistor M3. At the discharging phase, a matched NMOS transistor M10 will turn on accompany with the power NMOS transistor MN, and tie the point Y down to around zero voltage level. Therefore, a proportional sensing current Isense can be generated and converted to Vsense. With these two complementary current sensors, the full range current information can be obtained.
CIRCUIT IMPLEMENTATION
A. Complementary full range current sensor
B. Adaptively hysteretic window generator
The proposed CMAHC technique needs a full-range current sensor to continuously monitor the inductor current. The most intuitive way is to insert a sensing resistor in series with the inductor [2], however, this method engenders a voltage drop and degrades the conversion efficiency. Fig. 3 shows the structure of the current-mirror-based charging-path current sensor [3], [5]. The negative feedback loop formed by the transistors M3, M4, and M9 will force the points X and Y to become virtual short, and the current sensor is realized by a matched PMOS transistor M1 with the aspect ratio much
The schematic of the adaptive hysteretic window generator (AHWG) and ripple amplifier (RA) is shown in Fig. 5. In the proposed buck converter, two similar RAs have been used. The RA, which is followed by the AHWG, has a larger bandwidth, and therefore a pair of fast response hysteretic thresholds can be obtained. According to the output voltage level, the hysteretic window is adjusted rapidly from this path. This property helps the converter to reduce the reaction time under
951
TABLE I. PERFORMANCE SUMMARY AND COMPARISON
This work
TPE 2007 [4]
JSSC 2004 [5]
TCAS-II 2007 [6]
0.25μm CMOS 4.7 10 3.3 1.8 500KHz-1.5MHz Current-Mode Hysteretic
0.6μm CMOS 4.7 10 3.6 2.5 1.1MHz Current-Mode PWM
0.6μm CMOS 4.7 10 3.6 2.1 500KHz Current-Mode PWM
0.35μm CMOS 4.7 10 3.3 2.0 500KHz Current-Mode PWM
Compensation components
None
CFB=22pF
CC=1nF RZ
