A Current-Mode Non-inverting CMOS
Buck-Boost DC-DC Converter
Jong-Ha Park1, Hoon Kim2, Hee-Jun Kim1
1
Dept. of Electronics, Electrical Control, and Instrumentation Eng., Hanyang University, South Korea
2
Dept. of Semiconductor Engineering, Cheongju University, South Korea
E-mail: hjkim@hanyang.ac.kr
Abstract — This paper presents a current-mode control noninverting buck-boost converter. The proposed circuit is
controlled by the current mode and operated in three operation
modes which are buck, buck-boost, and boost mode. The
operation mode is automatically determined by the ratio between
the input and output voltages. The proposed circuit is simulated
by HSPICE with 0.5 μm standard CMOS parameters. Its input
voltage range is 2.5-5 V, and the output voltage range is 1.5-5 V.
The maximum efficiency is 92% when it operates in buck mode.
I.
INTRODUCTION
Increasing the use of mobile devices today requires
efficient power saving solutions to improve the battery life.
The power management systems are used to generate
constant or variable voltage from battery sources having a
wide terminal voltage variation (e.g., 0.9-1.8 V for
NiCd/NiMH, 2.7-4.2 V for Li-ion). The desired output
voltage can be higher or lower than the battery voltage,
thereby requiring a converter capability of both step-up and
step-down [1].
The trend in portable applications is to use topologies that
incorporate less number of external components. The ability
to work over a wide input voltage range supplying a high
output current makes these topologies an attractive choice
[2].
This paper presents an integrated current-mode control
buck-boost converter with various load condition. The
operation and principle of the proposed buck-boost converter
is described in Section II. The simulation results of the
proposed circuit are presented in Section III.
II. CIRCUIT PRINCIPLE AND OPERATION
A. Buck-Boost Converter with Three Operation Modes
Figure 1 shows a block diagram of the proposed circuit. It
consists of four power switches, current mode controller,
and operation mode controller. It has three operation modes
which are buck, buck-boost, and boost mode. The
conventional non-inverting buck-boost DC-DC converter
uses four switches at every cycle. It causes high switching
power losses. The buck-boost DC-DC converter which has
three operation modes was reported to overcome this
problem. It reduces the switching power loss by two
switches are switching when it operates in buck or boost
mode. The conventional buck-boost converter which has
three operation modes is used for a power supply of the
power amplifier. It needs two operation modes, buck or
boost mode. To reduce the power consumption of the power
amplifier, it operates in the buck mode when the power
amplifier is the idle state. It operates in the boost mode when
the power amplifier is the active state. The operation mode
of the conventional buck-boost converter is determined by
the external signal.
The operation mode of the proposed circuit is automatically
controlled by the ratio between the input and output voltage.
Figure 1. Block diagram of the proposed circuit
B. Current Mode Controller
Operation
Mode Control
Sensed
Current
Over Current
Detector
Compensation
Ramp
Vsum
Gate Driver
and
Dead Time
Control
Q
Gate Drive
Signals
Vref
R
S
Vfb
Comparator
Error
Amplifier
Clock
Figure 2. Block diagram of the current-mode controller
Figure 2 shows a block diagram of the current mode
controller. The proposed circuit operates in buck, buck-boost,
or boost modes by operating of power switches. The
controller is consist of operation mode controller, current
sensing circuit, dead time controller, and gate drive
controller. The operation mode is determined by the
1-4244-2491-7/09/$20.00 ©2009 IEEE
(a) Circuit diagram
(b) Timing diagram
Figure 3. Schematic of the dead-time and gate drive controller
operation mode controller. When the operation mode is
determined, it has to drive different pairs of power switches
as an operation mode.
Table 1 shows the state of power switches at each operation
modes. In the table, two switches are driving by PWM
signals when it operates in buck or boost operation mode.
Four switches are driving by PWM signals, when it operates
in the buck-boost mode. Figure 3 shows the schematic of the
dead time controller and the gate drive controller. It makes
four gate driving signals by using a PWM signal.
consists of resistors, logic gates, and latches. The range of
each operation mode is controlled by resistors.
TABLE I. STATE OF SWITCHES AT EACH OPERATION MODE
Mp1
Buck
Buck-Boost
Boost
On
On
On
Buck
Buck-Boost
Boost
Off
Off
On
Mp2
On Time
On
Off
Off
Off Time
On
On
On
Mn1
Mn2
Off
Off
Off
Off
On
On
On
On
Off
Off
Off
Off
Figure 4. Schematic of the operation mode controller
Since MOSFETs are used instead of a shottkey diode, it is
able to turn on p and n channel MOSFET at the same time. It
causes lots of power dissipation and unstable operation of all
circuitry blocks. To avoid this, the switches have to be
controlled by non-overlapping signals. Figure 3 (b) shows
timing diagram of the deadtime controller in the continuous
current mode (CCM) and the discontinuous current mode
(DCM). In the figure, Vs means the reverse current detecting
signal. The deadtime controller is shown by the dashed box
in the figure 3(a).
C. Operation-Mode Controller
Figure 4 shows a block diagram of the operation-mode
controller. This circuit determines the operation mode by the
ratio between the input voltage and the output voltage. It has
a hysteresis to prevent the oscillation of the operation mode.
If the operation mode is controlled without the hysteresis,
the operation mode can oscillate at the edge of each mode. It
makes that the output voltage is unstable. Figure 5 shows the
transfer characteristic of the operation-mode controller. It
Figure 5. Transfer characteristic of the operation mode
controller.
D. Current Sensing Circuit
The current sensing circuit is one of the most important
building blocks in current mode control. The SenseFET
current sensing circuit is adapted. Figure 6 shows a
schematic of the current sensing circuit. It has a high
accuracy and noise performance. It can operate in low power
supply voltage. And it can be easily compensated and has
high speed response.
In the figure 7, the current sensing circuit is shown by the
dashed box. The relationship of the sensed current and the
inductor current can be determined by the aspect ratio of Ms
and Mp1.
VIN
VIN
VGATE
Mp1
MS
(b) Buck-boost mode
Lex
Vsense
Mn1
Vbias
Figure 6. Schematic of the current sensing circuit
III.
SIMULATION RESULTS
HSPICE simulation program was used to verify operations
of the proposed circuit with 0.5μm CMOS standard process
parameter. The reference voltage, VREF, is 1.2V, and peak-topeak voltage of the saw-tooth wave, VM, is 2V. The value of
components are selected as the external capacitor is 10μF, the
external inductor is 20μH.
TABLE II. SUMMARY OF SIMULATION RESULTS
Parameter
Min
Typ
Max
Units
Vin
2.5
5
V
Vout
1.5
5
V
Iout
50mA
1.5A
A
fs
1.2
1.3
1.47
MHz
Efficiency
92
%
(c) Boost mode
Figure 7. Simulated waveforms
Figure 7 shows various waveforms of the proposed circuit
when it operates in each mode. It shows the output voltage and
operation mode control signals. The maximum efficiency is
measured as 92% when it operates in the buck mode. Table 2
shows the summary of simulation results.
IV.
CONCLUSION
This paper presents a current-mode control non-inverting
CMOS buck-boost DC-DC converter with three operation
modes. Its operation and performance were verified by
HSPICE. The simulation results show that the proposed circuit
can be applied for battery operation systems have wide supply
voltage ranges.
REFERENCES
[1]
[2]
[3]
(a) Buck mode
Biranchinath Sahu, et al., A High-Efficiency, Dual-Mode, Dynamic,
Buck-Boost Power Supply IC for Portable Applications, in proc.
VLSID’05, pp. 858-861, 2005.
Biranchinath Sahu, et al., A Low Voltage, Dynamic, Noninverting,
Synchronous Buck-Boost Converter for Portable Applications, IEEE
Trans. Power Electronics, Vol. 19, No. 2, pp. 443-452, 2004.
F.-F. Ma, W.-Z. Chen, and J.-C. Wu, A Monolithic Current-Mode Buck
Converter With Advanced Control and Protection Circuits, IEEE Trans.
Power Electronics, Vol. 22, No. 5, pp. 1836-1846, 2007.