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Linear Technology LTC3558 Manual

Usb battery charger with buck and buck-boost regulators.
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FEATURES
Battery Charger
n
Standalone USB Charger
n
Up to 950mA Charge Current Programmable via
Single Resistor
n
HPWR Input Selects 20% or 100% of Programmed
Charge Current
n
NTC Input for Temperature Qualifi ed Charging
n
Internal Timer Termination
n
Bad Battery Detection
Switching Regulators (Buck and Buck-Boost)
n
Up to 400mA Output Current per Regulator
n
2.25MHz Constant-Frequency Operation
n
Power Saving Burst Mode
Low Profi le, 20-Lead, 3mm × 3mm QFN Package
n
APPLICATIONS
n
SD/Flash-Based MP3 Players
n
Low Power Handheld Applications
TYPICAL APPLICATION
USB Charger Plus Buck Regulator and Buck-Boost Regulator
USB (4.3V TO 5.5V)
V
CC
1μF
1.74k
PROG
NTC
LTC3558
CHRG
SUSP
HPWR
DIGITAL
CONTROL
MODE
EN1
EN2
EXPOSED
GND
PAD
®
Operation
BAT
+
SINGLE
PV
IN1
Li-lon CELL
(2.7V TO 4.2V)
PV
IN2
10μF
1.2V AT 400mA
SW1
4.7μH
10pF
324k
FB1
SWAB2
649k
2.2μH
3.3V AT 400mA
SWCD2
V
OUT2
121k
324k
33pF
FB2
15k
105k
330pF
10pF
V
C2
3558 TA01
Linear USB Battery Charger
Buck-Boost Regulators
DESCRIPTION
®
The LTC
3558 is a USB battery charger with dual high ef-
fi ciency switching regulators. The device is ideally suited
to power single-cell Li-Ion/Polymer based handheld ap-
plications needing multiple supply rails.
Battery charge current is programmed via the PROG pin
and the HPWR pin with capability up to 950mA of current
at the BAT pin. The CHRG pin allows battery status to be
monitored continuously during the charging process. An
internal timer controls charger termination.
The part includes monolithic synchronous buck and buck-
boost regulators that can provide up to 400mA of output
current each and operate at effi ciencies greater than 90%
over the entire Li-Ion/Polymer battery range. The buck-
boost regulator can regulate its programmed output voltage
at its rated deliverable current over the entire Li-Ion range
without drop out, increasing battery runtime.
The LTC3558 is offered in a low profi le (0.75mm), thermally
enhanced, 20-lead (3mm × 3mm) QFN package.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
10μF
22μF
LTC3558
with Buck and
Demo Board
3558f
1

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Summary of Contents for Linear Technology LTC3558

  • Page 1 SD/Flash-Based MP3 Players enhanced, 20-lead (3mm × 3mm) QFN package. Low Power Handheld Applications , LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION...

  • Page 2: Absolute Maximum Ratings

    LTC3558 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) (Transient); TOP VIEW t < 1ms and Duty Cycle < 1% ....... –0.3V to 7V (Static) ..........–0.3V to 6V 20 19 18 17 16 BAT, CHRG ........... –0.3V to 6V PROG, SUSP .........–0.3V to (V + 0.3V)
  • Page 3 LTC3558 ELECTRICAL CHARACTERISTICS denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T = 25°C. V = 5V, BAT = PV = PV = 3.6V, R = 1.74k, unless otherwise noted. PROG SYMBOL...
  • Page 4 LTC3558 ELECTRICAL CHARACTERISTICS denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T = 25°C. V = 5V, BAT = PV = PV = 3.6V, R = 1.74k, unless otherwise noted. PROG SYMBOL...
  • Page 5 LTC3558 ELECTRICAL CHARACTERISTICS denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T = 25°C. V = 5V, BAT = PV = PV = 3.6V, R = 1.74k, unless otherwise noted. PROG SYMBOL...
  • Page 6 LTC3558 TYPICAL PERFORMANCE CHARACTERISTICS = 25°C, unless otherwise noted. Battery Regulation (Float) Voltage Suspend State Supply and BAT Battery Regulation (Float) vs Battery Charge Current, Currents vs Temperature Voltage vs Temperature Constant-Voltage Charging 4.24 4.205 = 5V 4.200 4.23 4.195 4.22...
  • Page 7 LTC3558 TYPICAL PERFORMANCE CHARACTERISTICS = 25°C, unless otherwise noted. Recharge Threshold Battery Charger FET SUSP/HPWR Pin Rising vs Temperature On-Resistance vs Temperature Thresholds vs Temperature = 5V = 5V = 4V = 200mA EN1 = EN2 = 0V –35 –15 –55...
  • Page 8 LTC3558 TYPICAL PERFORMANCE CHARACTERISTICS = 25°C, unless otherwise noted. Buck and Buck-Boost Regulator Buck and Buck-Boost Regulator Undervoltage Thresholds Enable Thresholds Buck Regulator Input Current vs vs Temperature vs Temperature Temperature, Burst Mode Operation 1200 2.750 BAT = PV = PV = 3.6V...
  • Page 9 LTC3558 TYPICAL PERFORMANCE CHARACTERISTICS = 25°C, unless otherwise noted. Buck Regulator Buck Regulator Pulse Skip Mode Operation Buck Regulator Start-Up Transient Burst Mode Operation 20mV/ 20mV/ 500mV/DIV DIV (AC) DIV (AC) INDUCTOR CURRENT 2V/DIV 2V/DIV = 200mA/ INDUCTOR INDUCTOR CURRENT...
  • Page 10 LTC3558 TYPICAL PERFORMANCE CHARACTERISTICS = 25°C, unless otherwise noted. Buck-Boost Effi ciency Buck-Boost Regulator vs Load Current Effi ciency vs Input Voltage = 3.3V = 3.3V = 10mA LOAD = 1mA 3.6V LOAD 4.2V 2.7V = 100mA LOAD = 400mA LOAD 2.7V...
  • Page 11 LTC3558 PIN FUNCTIONS GND (Pin 1): Ground. Connect to Exposed Pad (Pin 21). (Pin 14): Output of the Error Amplifi er and Voltage Compensation Node for the Buck-Boost Regulator. Ex- BAT (Pin 2): Charge Current Output. Provides charge cur- ternal Type I or Type III compensation (to FB2) connects rent to the battery and regulates fi...

  • Page 12: Block Diagram

    LTC3558 PIN FUNCTIONS of the full-scale charge current), unresponsive battery (Pin 20): Battery Charger Input. A 1μF decoupling (i.e., the battery voltage remains below 2.9V after one half capacitor to GND is recommended. hour of charging) and battery temperature out of range.
  • Page 13 LTC3558 OPERATION The LTC3558 is a linear battery charger with a monolithic For proper operation, the BAT, PV and PV pins synchronous buck regulator and a monolithic synchro- must be tied together, as shown in Figure 1. Cur- nous buck-boost regulator. The buck regulator is inter- rent being delivered at the BAT pin is 500mA.
  • Page 14 LTC3558 APPLICATIONS INFORMATION when V falls to within V (typically 50mV) of the enters constant-voltage mode, the 4-hour timer is started. DUVLO BAT voltage. After the safety timer expires, charging of the battery will discontinue and no more current will be delivered.
  • Page 15 Table 1. CHRG Output Pin of the power handling capability with a given circuit board MODULATION design without risk of damaging the LTC3558 or external (BLINK) components. The benefi t of the LTC3558 battery charger STATUS...
  • Page 16 LTC3558 APPLICATIONS INFORMATION NTC Thermistor value of R25 or approximately 54k (for a Vishay “Curve 1” thermistor, this corresponds to approximately 40°C). If The battery temperature is measured by placing a nega- the battery charger is in constant-voltage mode, the safety tive temperature coeffi...
  • Page 17 LTC3558 APPLICATIONS INFORMATION Alternate NTC Thermistors and Biasing Therefore, the hot trip point is set when: The battery charger provides temperature qualifi ed NTCHOT = 0 349 • • charging if a grounded thermistor and a bias resistor are NTCHOT connected to the NTC pin.
  • Page 18 LTC3558 APPLICATIONS INFORMATION to 46.4k. With this value of R , the cold trip point is For example, to set the trip points to 0°C and 45°C with about 16°C. Notice that the span is now 44°C rather than a Vishay Curve 1 thermistor choose: the previous 40°C.
  • Page 19 • – ° 5V WALL ADAPTER 950mA I BATTERY The LTC3558 can be used above 70°C, but the charge cur- CHARGER POWER rent will be reduced from 500mA. The approximate current 500mA I Li-Ion PROG at a given ambient temperature can be calculated: BATTERY °...
  • Page 20 USB voltage. To prevent excessive voltage from damag- be kept to a minimum. With no additional capacitance on ing the LTC3558 during a hot insertion, the soft connect the PROG pin, the charger is stable with program resistor circuit in Figure 7 can be employed.
  • Page 21 Buck Switching Regulator General Information Buck Switching Regulator Output Voltage Programming The LTC3558 contains a 2.25MHz constant-frequency current mode buck switching regulator that can provide The buck switching regulator can be programmed for output voltages greater than 0.8V. The output voltage up to 400mA.
  • Page 22 LTC3558 APPLICATIONS INFORMATION switch. During each cycle, a current comparator compares powered down, helping conserve battery power. When the peak inductor current to the output of an error amplifi er. the output voltage drops below a pre-determined value, The output of the current comparator resets the internal...
  • Page 23 LTC3558 APPLICATIONS INFORMATION Buck Switching Regulator Soft-Start Operation Buck Switching Regulator Inductor Selection Soft-start is accomplished by gradually increasing the peak The buck switching regulator is designed to work with inductor current for each switching regulator over a 500μs inductors in the range of 2.2μH to 10μH, but for most period.
  • Page 24 Table 2 shows several inductors that work well with the for most applications. For good transient response and LTC3558 buck switching regulator. These inductors offer stability the output capacitor should retain at least 4μF a good compromise in current rating, DCR and physical of capacitance over operating temperature and bias volt- size.
  • Page 25 APPLICATIONS INFORMATION Buck-Boost Switching Regulator the converter will operate in four-switch mode. While operating in four-switch mode, switches turn on as per The LTC3558 contains a 2.25MHz constant-frequency, → the following sequence: switches A and D switches A voltage mode, buck-boost switching regulator. The regu- →...
  • Page 26 The unity-gain frequency of the error amplifi er with the Closing the Feedback Loop Type I compensation is given by: The LTC3558 incorporates voltage mode PWM control. The control to output gain varies with operation region (buck, boost, buck-boost), but is usually no greater than 20. The π...
  • Page 27 LTC3558 APPLICATIONS INFORMATION Most applications demand an improved transient response at the fi lter double pole. If they are placed at too low of a to allow a smaller output fi lter capacitor. To achieve a higher frequency, they will introduce too much gain to the system bandwidth, Type III compensation is required.
  • Page 28 LTC3558 APPLICATIONS INFORMATION Input Current Limit Buck-Boost Switching Regulator Inductor Selection The input current limit comparator will shut the input PMOS The buck-boost switching regulator is designed to work with inductors in the range of 1μH to 5μH. For most switch off once current exceeds 700mA typical.
  • Page 29 In order to deliver maximum charge current under all Low ESR (equivalent series resistance) ceramic capacitors conditions, it is critical that the backside of the LTC3558 should be used at both the buck-boost regulator input be soldered to the PC board ground.
  • Page 30 Figure 12. Li-Ion to 3.3V at 400mA, 1.8V at 400mA and USB-Compatible Battery Charger in Figure 13. CHRG has a LED to provide a user with a As shown in Figure 12, the LTC3558 can be operated with no battery connected to the BAT pin. A 1Ω resistor visual indication of battery charge status.
  • Page 31 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
  • Page 32 : 2.7V to 5.5V, 3mm × 3mm DFN-10 Package Synchronous Buck Output: 0.8V to V , Buck Input V Hot Swap is a trademark of Linear Technology Corporation. 3558f LT 0408 • PRINTED IN USA Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417...