Datasheet LTC3556, LTC3566, LTC3567 Datasheet (LINEAR TECHNOLOGY)

L DESIGN FEATURES
Li-Ion
0.8V TO 3.6V/400mA
3.3V/25mA
0.8V TO 3.6V/400mA
0.8V TO 3.6V/1A
RST
2
OPTIONAL
0V
T
TO OTHER LOADS
+
LTC3555/LTC3555-X
TRIPLE
HIGH EFFICIENCY
STEP-DOWN
SWITCHING
REGULATORS
I2C PORT
ALWAYS ON LDO
MEMORY
RTC/LOW POWER LOGIC
I2C
CORE
I/O
µPROCESSOR
USB/WALL
4.35V TO 5.5V
CHARGE
ENABLE
CONTROLS
USB COMPLIANT
STEP-DOWN REGULATOR
CC/CV
BATTERY
CHARGER
5
1
2
3
CURRENT CONTROL
New Family of Integrated Power Controllers Combine Fast Battery Charging, PowerPath Control and Efficient DC/DC Converters in Less Than 20mm2
Introduction
The quickest way to build an efficient power system for a battery-powered portable application is to use an IC that combines all power control functions into a single chip, namely a Power Management Integrated Circuit (PMIC). PMICs seamlessly manage power flow from various power sources (wall adapters, USB and batteries) to power loads (device systems and the charging battery), while maintaining current limits where required (such as that specified for USB). To this end, PMICs typically feature built-in PowerPath™ control, DC/DC conver-
Table 1. Power management ICs with Li-ion/polymer battery chargers
PowerPath
Part Number
LTC3555/-1/-3 Switching I2C 1A, 400mA × 2 25mA
Topology Interface
Figure 1. High efficiency PowerPath manager and triple step-down regulator
Integrated Converters and Load Current Capabilities
by Sam Nork
PackageBuck Buck-Boost Boost LDO
4mm × 5mm
QFN-28
LTC3556 Switching I2C 400mA × 2 1A 25mA
LTC3566 Switching 1A 25mA
LTC3567 Switching I2C 1A 25mA
LTC3586* Switching 400mA × 2 1A 0.8A 20mA
LTC3557/-1 Linear 600mA, 400mA × 2 25mA
Linear Technology Magazine • September 2008
LTC3455 Linear 600mA, 400mA Controller
LTC3558 400mA 400mA
LTC3559/-1 400mA × 2
*For an application of the LTC3586 see “Complete Power Solution for Digital Cameras and Other Complex Compact Portable Applications” in this issue
4
4mm × 5mm
QFN-28
4mm × 4mm
QFN-24
4mm × 4mm
QFN-24
4mm × 6mm
QFN-38
4mm × 4mm
QFN-28
4mm × 4mm
QFN-24
3mm × 3mm
QFN-20
3mm × 3mm
QFN-16
DESIGN FEATURES L
Li-Ion
PGOODALL
0.8V TO 3.6V/400mA
3.3V/25mA
2.5V to 3.3V/1A
0.8V TO 3.6V/400mA
OPTIONAL
0V
T
TO OTHER LOADS
+
LTC3556
DUAL HIGH EFFICIENCY
BUCKS
HIGH EFFICIENCY
BUCK-BOOST
I2C PORT
ALWAYS ON LDO
MEMORY CORE µP
RTC/LOW POWER LOGIC
HDD/IO
3556 TA01
USB/WALL
4.5V TO 5.5V
CHARGE
I2C
USB COMPLIANT
STEP-DOWN REGULATOR
CC/CV
BATTERY
CHARGER
SEQ
ENALL
3
1
2
3
40
50
60
70
80
30
20
10
0
90
100
V
IN3
(V)
2.7
EFFICIENCY (%)
3.1
3.5 3.9 4.3 4.7
V
OUT3
= 3.3V
TA = 27°C
I
OUT3
= 200mA
I
OUT3
= 50mA
I
OUT3
= 1000mA
BATTERY VOLTAGE (V)
2.8
0
CHARGE CURRENT (mA)
200
3.2
3.6
3.8
100
700
400
500
600
300
3
3.4
4
4.2
BATTERY CHARGE CURRENT
500mA USB CURRENT LIMIT
EXTRA CURRENT FOR FASTER CHARGING
V
BUS
= 5V 5X MODE BATTERY CHARGER PROGRAMMED FOR 1A
sion and battery charging functions. PMICs can be applied in everything from consumer electronics such as MP3 players and Bluetooth headsets to specialized portable medical and industrial equipment.
Table 1 shows the wide variety of integrated charger and DC/DC com­binations now available from Linear Technology. The latest additions to the family, the LTC3555, LTC3556, LTC3566, LTC3567 and LTC3586, are primarily targeted toward relatively high power Li-Ion applications and contain blocks capable of high effi­ciency at high current levels. (To see an application of the LTC3586, see “Complete Power Solution for Digital Cameras and Other Complex Compact Portable Applications” in the Design Ideas section of this issue.)
The most noteworthy feature of the new parts is the use of a proprietary switching PowerPath design, which improves efficiency over linear power path or battery fed solutions.
Switching PowerPath Control Efficiently Harnesses Available External Power
To speed up charging, some of Linear’s new PMICs employ a unique current limited synchronous buck switch­ing charger architecture that uses more power from the USB or adapter than other topologies. This is a big improvement over battery fed and linear PowerPath control schemes. (For a more detailed description of the switching PowerPath architecture,
on” capability if the battery is dead or missing (as long as the load current is less than the input current limit). However, neither a linear charger nor linear power manager is well-suited for high current charging due to poor efficiency under certain conditions.
power, but charging/powering from the USB host is complicated by the host’s 2.5W limit. To take advantage of the limited USB power, all components
Figure 2. Switching power manager charge current vs battery voltage with a 500mA input current limit. Peak charge current = 700mA.
in the power path must be as efficient as possible.
is a battery-tracking (Bat-Track™) see the cover article in the June 2008 issue of Linear Technology magazine titled “Speed Up Li-ion Battery Charg­ing and Reduce Heat with a Switching PowerPath Manager.”)
For instance, portable products with large capacity batteries (1Ahr plus) face a direct tradeoff between charge time and charger power dis­sipation—especially when a linear charging method is used. At relatively low charge currents, a linear charger dissipates a modest amount of power, but at currents required to quickly charge high capacity batteries, a linear charger can dissipate 2W or more.
A switching PowerPath topology is an improvement over the commonly
synchronous buck design with logic programmable input current limit to ensure USB compatibility. When USB or adapter power is available, the LTC35xx power manager generates a V The 300mV difference voltage is suf­ficient to keep the battery charger just out of dropout and deliver the programmed charge current at high efficiency. As with linear power manag­ers, the load current is provided first, and current that is left over is directed to the battery. Input current limit is controlled via an external resistor to set absolute current and two logic pins to control the ratio (e.g. 100mA,
500mA, 1A and Suspend). used linear PowerPath topology, and both are an improvement over battery fed applications. A linear PowerPath powers the application directly from an external source rather than from the battery itself and provides “instant
with a completely discharged battery
is achievable vs 60% or so for a linear
charger. Or said another way, the
switching power path dissipates only
50% of the power dissipated by a linear
USB is now a common source of
A key attribute in these new PMICs
supply equal to V
OUT
+ 300mV.
BAT
Charging efficiency of over 80%
Linear Technology Magazine • September 2008
Figure 3. 1A buck-boost efficiency vs VIN (LTC3556, LTC3566/7, LTC3586)
5
GND
ILIM
DECODE
LOGIC
I2C PORT
SWAB1
V
IN1
V
C1
FB1
DV
CC
SCL
EN1
CHRGEN
CHRGEN
SDA
1A, 2.25MHz
BUCK-BOOST
REGULATOR
ENABLE
MODE
SWCD1
V
OUT1
D/A
4
6, 12, 17, 25
V
IN4
LTC3586
L
SW4
R1 C
OUT
C
PL
R2
V
OUT4
FB4
Li-Ion
FAULT
0.8V TO 3.6V/400mA
5V/800mA
3.3V/20mA
2.5V to 3.3V/1A
0.8V TO 3.6V/400mA
OPTIONAL
0V
T
TO OTHER LOADS
+
LTC3586
DUAL HIGH EFFICIENCY
BUCKS
HIGH EFFICIENCY
BUCK-BOOST
HIGH EFFICIENCY
BOOST
ALWAYS ON LDO
MEMORY/ CORE µP
RTC/LOW POWER LOGIC
I/O SYSTEM
USB/WALL
4.5V TO 5.5V
CHARGE
I
LIM
USB COMPLIANT
STEP-DOWN REGULATOR
CC/CV
BATTERY
CHARGER
MODE
EN
2
4
1
2
AUDIO/ MOTOR
4
3
CURRENT CONTROL
L DESIGN FEATURES
charger under worst case conditions. The LTC35xx switching power man­agers can charge at up to 1.2A max and provide seamless switchover to battery power when the external power is removed. In USB applications, the constant power (vs constant current) nature of the switching PowerPath controller makes it possible to charge with more than 500mA from a fixed 500mA USB input source, as shown in Figure 2.
Higher Current Chargers Go Hand-In-Hand with Higher Current Regulators
An obvious companion to a high performance battery charger is a cor­responding set of DC/DC regulators with similar peak current handling and high efficiency. As shown in Table 1, the latest PMICs offer between one and four DC/DCs of varied topologies with peak currents reaching 1A. The new parts provide a variety of specific options to meet the high performance needs of specific applications.
Need a Buck-Boost? Not a Problem…
Most high end portable products need a minimum of three key power sup­plies: one for the µP core (~1.0V–1.5V), one for memory (~1.8V), and one for the I/O and main system supply (~3.3V). The LTC3555 covers all three with its built-in three synchronous bucks. However, some applications, particularly the more feature-rich va­riety, face occasional high peak power transients during wireless transmis­sions or when a hard drive spins up. The effective voltage of the battery drops during these transient currents due to the battery series resistance
Figure 5. Boost converter application circuit
6
Figure 4. The LTC3586 is a high efficiency PowerPath controller, always­on LDO, dual buck, buck-boost, plus boost—all in a 4mm × 6mm package
(BSR), trace impedance or power path losses. This poses a problem for the
3.3V supply, which can drop out of regulation even if the battery is still significantly charged. In such cases, a buck-boost regulator can save the day by riding through such battery transients—maintaining regulation as if nothing happened. Several new PMICs contain buck-boost DC/DCs specifically for this purpose. As shown in Figure 3, the PMIC buck-boosts can provide a high efficiency 3.3V output with an input that ranges from 2.7V to 5.5V.
The LTC3566 and LTC3567 prod­ucts include a 1A buck-boost supply in addition to a high performance
Figure 6. The LTC3567 I/O and DC/DC output voltage control interface
switching PowerPath controller as cor­nerstone high performance building blocks. The LTC3556 ups the integra­tion further by including two 400mA buck regulators to accompany the charger and buck-boost supply. The LTC3586 contains all of the blocks of the LTC3556, but ups the integration one step further…
Need an Additional 5V Boost? The LTC3586 Has It Covered
While the buck-boost regulators are capable of regulating a 5V supply, some applications require both. To meet this need, the LTC3586 includes not only a full complement of low volt­age regulators, it also includes a high
continued on page 15
Linear Technology Magazine • September 2008
DESIGN FEATURES L
the range of 1.4V to 3.3V. If possible, using a lower OV
can reduce power
DD
consumption. The termination scheme is largely based on the receiver. When choosing the OV
voltage, refer to the
DD
receiver’s data sheet to terminate the CML lines properly.
CML uses true double termination. Generally, LVDS is only terminated at the receiver, which means that any signal reflection back to the source reflects back to the receiver with little attenuation. This limits the data rate and trace length that LVDS can drive. The truly differential nature of CML radiates less energy than LVDS and CMOS signals, allowing devices to be in closer proximity to antennas, mix­ers or other sensitive analog front end systems. CML also has common mode termination. This gives CML a better common mode behavior than LVDS. LVDS is only terminated differentially, which does not reject any common mode signal that may appear on the transmission line—another limiting factor in LVDS signaling.
CML Power Consumption
With a constant 16mA of bias current and a voltage swing of 800mV differen­tial, CML logic consumes a moderate amount of power. For an equal data rate, CML logic consumes less total power than PECL and LVPECL. A single CML driver uses more power than a single LVDS driver, but only marginally more that the three pairs of LVDS drivers required for a typical LVDS serial bus.
8B/10B Encoding Makes for Simple Connection
The 8B/10B encoding process results in an average DC offset of zero, allowing the data to be routed through trans­formers or fiber channel transceivers that can provide isolation between the digital and analog realm. 8B/10B encoding also does not require a fram­ing signal or a data clock, whereas both are required in traditional serial communication. 8B/10B encoding transmits data over a single pair of data lines, whereas a typical serial
ADC requires three or more pairs, and a typical parallel ADC can require more than 16 pairs.
The complexity of decoding 8B/10B lies in the receiver. Fortunately Xilinx, Altera and Lattice have solutions to receive data from the LTC2274 and decode the 8B/10B data, simplifying the collection of 8B/10B data. Other 8B/10B decoding solutions may be available. The FPGA required to receive data from the LTC2274 must be able to receive high speed serial transmis­sions of 2GHz or more.
Conclusion
Without sacrificing resolution or sample rate, the LTC2274 delivers full 16-bit performance at 105Msps over a single pair of transmission lines, greatly simplifying layout and saving valuable board space. This mitigates interaction with other circuitry in software defined radio, base station or industrial applications which involve many channels of an ADC routed to one FPGA.
L
LTC35xx, continued from page 6
power synchronous boost converter (Figure 5).
The fully integrated boost in the LTC3586 can regulate up to a 5V out­put with up to 800mA from a battery voltage as low as 3V. The regulator has built in output disconnect making it well-suited for USB OTG supplies or for powering motors in printer and camera applications. The current mode synchronous boost is internally compensated and operates at a fixed
2.25MHz switching frequency. Pulse­skipping at low loads achieves low noise output for driving high power audio circuits.
I2C, Programmable Sequencing and Easy I/O
Despite the progress in new cutting edge features and design, one old problem does not go away: power supply control. Power supplies require startup and power down sequencing, fault detection/reporting/handling and voltage and operating mode ad­justments. Getting it all right can be a system control nightmare depending
on the complexity and limitations of the power supply circuits.
The LTC35xx family provides very simple and flexible control of all es­sential power supply functions. The LTC3566 and LTC3586 employ dedi­cated I/O control pins for enabling, disabling and changing DC/DC operating modes. Voltages on these parts are fixed and set with exter­nal resistor dividers. The LTC3555, LTC3556 and LTC3567 accommodate either I2C control or simple I/O pins to control the supplies. The LTC3556 provides a three-state SEQ pin to al­low the power up sequence of its three DC/DC converters to be programmed via pin-strapping. Those parts with I2C V maximum V
control power-up at their
OUT
(as determined by the
OUT
FB servo point and external dividers) when enabled via simple I/O, and can independently reduce V
OUT
by as much as 50% in equal 16-step incre­ments via I2C.
All DC/DC converters in all the PMICs discussed here can survive an indefinite output fault. The parts
all provide a RST output and all con­verters are actively pulled down in shutdown to ensure proper power-up sequencing. The LTC3586 contains an additional fault handing feature that automatically powers down all DC/DC converters whenever a valid fault is detected. In short, the entire family is designed for simple, flexible and trouble-free control and operation.
Conclusion
Linear Technology’s latest PMIC products improve the performance and simplify the design of a wide va­riety of portable power management applications. Instead of kitchen sink alternatives with large packages, Linear Technology offers a number of devices with various feature mixes in small packages. These new PMICs are simple to use, highly integrated and high performance, allowing for shorter design times, greater PCB flexibility, and better power/thermal manage­ment than traditional solutions.
L
Linear Technology Magazine • September 2008
15
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