Dynamic power management for faster, more efficient battery charging

Dynamic power management for faster, more efficient battery charging
Power Management
Texas Instruments Incorporated
Dynamic power management for faster,
more efficient battery charging
By Samuel Wong
Systems Engineer
With the fast-growing demand for emerging portable
devices such as tablets and smartphones, there are many
new challenges in improving battery-operated system performance. The battery-management system must be intelligent to support different types of adapters and battery
chemistries and must provide fast charging with high efficiency. At the same time, it is important to provide a good
user experience with instant turn-on of the system, longer
battery run time, and fast charging. This article discusses
how to achieve fast battery charging and improve batterycharging performance with dynamic power management
(DPM). DPM helps to avoid system crashes and maximizes
the power available from the adapter. It can be based on
input current or input voltage, or combined with a batterysupplement mode. This article also discusses critical
design considerations for extending battery run time.
The lithium-ion (Li-Ion) battery is desirable for the evergrowing power need in portable devices because it has very
high energy density. Nowadays, it is common for a 10-inch
tablet to include a battery pack with 6- to 10-Ah capacity
to support a long run time. With the high-capacity battery,
it is critical for the portable device to have fast and efficient
charging for a good user experience. Additionally, tablets
require other features such as superior thermal perform­
ance and instant turn-on, even with a deeply discharged
battery. These requirements present a few technical challenges. One is how to maximize available power from the
power source to efficiently and quickly charge the battery
—while not crashing the power source. Another is how to
charge a deeply discharged battery while simultaneously
operating the system. Last is how to extend the battery
run time and improve thermal performance.
Dynamic power management (DPM)
How can available power be maximized to charge the battery quickly and efficiently? Every power source has its
output current, or power limit. For example, the maximum
output current is limited to 500 mA from a high-speed USB
(USB 2.0) port, and up to 900 mA from a SuperSpeed USB
(USB 3.0) port. The power source can crash if the system’s
power demand exceeds the power available from the power
source. When the battery is being charged, how can a
power-source crash be prevented while the power output
is being maximized? The following discussion presents
three control methods: DPM based on input current, DPM
based on input voltage, and DPM used with a batterysupplement mode.
Figure 1. DPM based on input current
IIN
Q1
VBUS
Q2
ICHG
Q3
–
+
Control
Loops
Q4
ISYS
IREF
–
VBAT
+
Introduction
VREG
DPM based on input current
Figure 1 shows a high-efficiency switch-mode charger with
DPM controls. MOSFETs Q2 and Q3 and inductor L make
up a synchronous switching buck-based battery charger.
Using a buck converter ensures that the adapter’s input
power is efficiently converted to achieve the fastest battery
charging. MOSFET Q1 is used as a battery reverse-blocking
MOSFET for preventing leakage from the battery to the
input through the body diode of MOSFET Q2. It also is used
as an input-current sensor to monitor the adapter current.
MOSFET Q4 is used to actively monitor and control the
battery-charging current to achieve DPM. When the input
power is sufficient to support both the system load and
battery charging, the battery is charged with the desired
charge-current value of ICHG. If the system load (ISYS) is
suddenly increased and its total adapter current reaches
the current-limit setting (IREF), the input-current regulation loop actively regulates and maintains the input current
at the predefined IREF input reference current. This is
achieved by reducing the charge current while giving
higher priority to powering the system so it can reach its
highest performance. Therefore, the input power is always
maximized without crashing the input-power source, while
the available power is dynamically shared between the
system and battery charging.
15
Analog Applications Journal
4Q, 2013
www.ti.com/aaj
High-Performance Analog Products
Power Management
Texas Instruments Incorporated
If a third-party power source is plugged into a system that
cannot identify its current limit, it is difficult to use DPM
based on limiting the input current. Instead, DPM is based
on the input voltage (Figure 2). Resistor dividers R1 and
R2 are used to sense the input voltage and are fed into
the error amplifier of the input-voltage regulation loop.
Simi­larly, if the system load is increased, causing the input
current to exceed the adapter’s current limit, the adapter
voltage starts to decrease and eventually reaches the predefined minimum input voltage. The input-voltage regulation loop is activated to maintain the input voltage at the
predefined level. This is achieved by automatically reducing
the charge current so that the total current drawn from
the input-power source reaches its maximum value without crashing the source. Therefore, the system can track
the adapter’s maximum input current. The input-voltage
regulation is designed to keep the voltage high enough to
fully charge the battery. For example, the voltage can be
set around 4.35 V to fully charge a single-cell, Li-Ion battery pack.
Battery-supplement mode
DPM based on input current or input voltage can draw the
maximum power from the adapter without crashing it. For
portable devices such as smartphones and tablets, the system load is usually dynamic with a high pulsating current.
What happens if the pulsating system’s peak power is higher
than the input power, even when the charge current is
already reduced to zero? The input-power source could
crash without active control.
One solution is to increase the adapter’s power rating,
but this increases the adapter’s size and cost. Another
solution is to temporarily have the battery provide additional power to the system by turning the MOSFET Q4 on
to discharge the battery instead of charging it. Combining
the DPM control and the battery-supplement mode allows
the adapter to be optimized to support the average power
instead of the maximum peak system power, reducing the
cost and achieving the smallest solution size.
Design considerations for improving
system performance
Portable systems such as tablets and smartphones require
instant turn-on to provide a good user experience. This
means that whether the battery is fully charged or deeply
discharged, the system will turn on instantly when an
adapter is plugged in.
Figure 2. DPM based on input voltage
VIN IIN
Q1
L
Q2
R1
ICHG
Q3
–
+
Control
Loops
VREF
Q4
–
R2
VBUS
ISYS
VBAT
+
DPM based on input voltage
VREG
As an example, suppose that a one-cell Li-Ion battery is
used for the systems in Figures 1 and 2. If the battery is
directly connected to the system without MOSFET Q4, the
system bus voltage (VBUS) is the same as the battery voltage. A deeply discharged battery with less than 3 V may
prevent system turn-on. The user may have to wait until
the battery is charged to 3.4 V before turning on the system. In order to support instant turn-on, MOSFET Q4 is
added to operate in linear mode to maintain the minimum
system-operation voltage while simultaneously charging a
deeply discharged battery. The minimum system voltage is
regulated by the switching converter, and the charge current from Q4 is regulated with a linear control loop. Once
the battery voltage reaches the minimum system voltage,
MOSFET Q4 is fully turned on. Its charge current is then
regulated by the duty cycle of the synchronous buck converter. So the system voltage is always maintained
between the minimum system-operation voltage and the
maximum battery voltage for powering the system.
In a 5-V USB charging system, all series resistance
between the power source and the battery contributes to
charging efficiency. This resistance in the charging path
consists of the ON resistance of FETs Q1, Q2, and Q4 and
about 250 mW from the USB cable. It is not unusual to have
a 4.5-V charger input after a cable voltage drop. Therefore,
it is critical to design a charger with the lowest possible
16
High-Performance Analog Products
www.ti.com/aaj
4Q, 2013
Analog Applications Journal
Power Management
Texas Instruments Incorporated
3.0
4.5
Voltage (bq24190)
2.5
4.2
Voltage (High RON)
2.0
3.9
1.5
Of course, the higher the battery capacity, the
longer is the battery run time. For a single-cell
1.0
operating system that usually requires a 3.3-V
output, the typical minimum system voltage is
0.5
around 3.4 V. If the ON resistance of MOSFET
Q4 is 50 mW, and the battery-discharge current
0
is 3 A, the battery cutoff voltage is 3.55 V. This
0
means that over 15% of the battery capacity is
unused. In order to maximize the battery run
time, the MOSFET Q4’s ON resistance must be
as small as possible. For instance, with an ON resistance
of 10 mW and the same peak battery-discharge current of
3 A, the battery cutoff voltage will be 3.43 V. This provides
10% more battery capacity than with an ON resistance of
50 mW.
Figure 4 shows an example of a high-efficiency, singlecell I2C battery charger with integrated MOSFETs. This
charger supports both USB and AC adapter inputs for tablets and portable media devices. All four power MOSFETs
are integrated, while MOSFETs Q1 and Q4 are used to
Current (High RON)
3.6
Current (bq24190)
Charge Voltage (V)
Extending battery run time
Figure 3. Effect of high ON resistance in the charging path
Charge Current (A)
FET ON resistance to minimize charging time.
Figure 3 compares the charging time of a design
using the Texas Instruments bq24190 USB/
adapter charger and an alternative design having
an extra 80 mW in the charging path. It can be
seen that, with a 4.5-V input voltage, the charging time of the bq24190 design is reduced by
20% compared with the other design.
3.3
VBUS = 4.5 V,
Battery Capacity = 14.8 Wh
50
100
150
Charge Time (minutes)
200
3.0
250
sense the input current and battery-charge current, further
minimizing the system’s solution size. This charger can
distinguish between a USB port and an adapter to quickly
set the correct input-current limit. Additionally, the charger can operate as a stand-alone charger with internal
default charge current, charge voltage, a safety timer, and
input-current limits—even when the system is turned off.
The charger also has a USB On-the-Go (OTG) function,
operating in boost mode to provide a 5-V, 1.3-A output at
the USB input from the battery.
Figure 4. High-efficiency, 4-A I2C switching charger with DPM
VBUS
bq24192
SW
Input: 3.9 to 17 V
L: 1.5 µH
System:
3.4 to 4.4 V
Q2
Q1
1 µF
2x 10 µF
VREF
Controller
Q3
PGND
VREF
SYS
STAT
SDA
SCL
INT
Host
OTG
CE
USB
PHY
Battery
BAT
Q4
VREF
1 µF
TS1
TS2
PSEL
17
Analog Applications Journal
4Q, 2013
www.ti.com/aaj
High-Performance Analog Products
Power Management
Thermal performance is critical for portable
devices with a very thin profile because users can
easily feel the heat dissipated from the printed
circuit board. This heat is due to components
that consume a lot of power, such as the battery charger. To combat this, a high-efficiency
charger and a good layout are very important.
To further improve the thermal performance,
a thermal-regulation loop is available in the
bq2419x family. It maintains the maximum junction temperature by reducing the charge current
once the device reaches the predefined junction
temperature. Figure 5 shows the measured
battery-charging efficiency in a bq24190 design.
Up to 94% efficiency can be achieved with a 5-V
USB input. With a 9-V input and a 4-A charge
current, there is only a 32°C temperature rise.
Figure 5. Measured battery-charging efficiency at
different charge currents
96
VBUS = 5 V
94
Efficiency (%)
Thermal performance
Texas Instruments Incorporated
92
VBUS = 9 V
90
88
VBUS = 12 V
86
84
0
0.5
1
1.5
2
2.5
3
Charge Current (A)
3.5
4
4.5
Conclusion
This article has shown that DPM based on either
input current or input voltage can be used to power portable devices, providing instant system turn-on while simultaneously charging the battery. It has also been shown that
adding a battery-supplement mode is critical for optimizing
power-system performance. Other design considerations
have also been discussed, such as instant turn-on with a
depleted battery, battery run time, charging-path resist­
ance, and thermal performance.
Related Web sites
Power Management:
www.ti.com/power-aaj
www.ti.com/battery-aaj
www.ti.com/bq24190-aaj
www.ti.com/bq24192-aaj
Subscribe to the AAJ:
www.ti.com/subscribe-aaj
18
High-Performance Analog Products
www.ti.com/aaj
4Q, 2013
Analog Applications Journal
TI Worldwide Technical Support
Internet
TI Semiconductor Product Information Center
Home Page
support.ti.com
TI E2E™ Community Home Page
e2e.ti.com
Product Information Centers
Americas Phone
+1(512) 434-1560
Brazil
Phone
0800-891-2616
Mexico
Phone
0800-670-7544
Fax
Internet/Email
+1(972) 927-6377
support.ti.com/sc/pic/americas.htm
Europe, Middle East, and Africa
Phone
European Free Call
International
Russian Support
00800-ASK-TEXAS
(00800 275 83927)
+49 (0) 8161 80 2121
+7 (4) 95 98 10 701
Note: The European Free Call (Toll Free) number is not active in
all countries. If you have technical difficulty calling the free call
number, please use the international number above.
Fax
Internet
Direct Email
+(49) (0) 8161 80 2045
www.ti.com/asktexas
asktexas@ti.com
Japan
Phone
Fax
Domestic
International
Domestic
0120-92-3326
+81-3-3344-5317
0120-81-0036
Internet/Email International
Domestic
support.ti.com/sc/pic/japan.htm
www.tij.co.jp/pic
Asia
Phone
International
+91-80-41381665
Domestic
Toll-Free Number
Note: Toll-free numbers do not support
mobile and IP phones.
Australia
1-800-999-084
China
800-820-8682
Hong Kong
800-96-5941
India
1-800-425-7888
Indonesia
001-803-8861-1006
Korea
080-551-2804
Malaysia
1-800-80-3973
New Zealand
0800-446-934
Philippines
1-800-765-7404
Singapore
800-886-1028
Taiwan
0800-006800
Thailand
001-800-886-0010
Fax
+8621-23073686
Emailtiasia@ti.com or ti-china@ti.com
Internet
support.ti.com/sc/pic/asia.htm
Important Notice: The products and services of Texas Instruments
Incorporated and its subsidiaries described herein are sold subject to TI’s
standard terms and conditions of sale. Customers are advised to obtain the
most current and complete information about TI products and services
before placing orders. TI assumes no liability for applications assistance,
customer’s applications or product designs, software performance, or
infringement of patents. The publication of information regarding any other
company’s products or services does not constitute TI’s approval, warranty
or endorsement thereof.
A090712
E2E is a trademark of Texas Instruments. All other trademarks are the property of
their respective owners.
© 2013 Texas Instruments Incorporated
SLYT546
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation
www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom
www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2013, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising