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LT1513/LT1513-2

sn1513 1513fas

SEPIC Constant- or

Programmable-Current/

Constant-Voltage Battery Charger

The LT

1513 is a 500kHz current mode switching regula-

tor specially configured to create a constant- or program-

mable-current/constant-voltage battery charger. In addition

to the usual voltage feedback node, it has a current sense

feedback circuit for accurately controlling output current

of a flyback or SEPIC (Single-Ended Primary Inductance

Converter) topology charger. These topologies allow the

current sense circuit to be ground referred and completely

separated from the battery itself, simplifying battery switch-

ing and system grounding problems. In addition, these

topologies allow charging even when the input voltage is

lower than the battery voltage. The LT1513 can also drive

a CCFL Royer converter with high efficiency in floating or

grounded mode.

Maximum switch current on the LT1513 is 3A. This allows

battery charging currents up to 2A for a single lithium-ion

cell. Accuracy of 1% in constant-voltage mode is perfect

for lithium battery applications. Charging current can be

easily programmed for all battery types.

DESCRIPTION

■

Charger Input Voltage May Be Higher, Equal to or

Lower Than Battery Voltage

■

Charges Any Number of Cells Up to 20V

■

1% Voltage Accuracy for Rechargeable Lithium

Batteries

■

100mV Current Sense Voltage for High Efficiency

(LT1513)

■

0mV Current Sense Voltage for Easy Current

Programming (LT1513-2)

■

Battery Can Be Directly Grounded

■

500kHz Switching Frequency Minimizes

Inductor Size

■

Charging Current Easily Programmable or Shut Down

FEATURES

INPUT VOLTAGE (V)

CURRENT (A)

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

LT1513 • TA02

12V

INDUCTOR = 10µH

ACTUAL PROGRAMMED CHARGING CURRENT WILL BE

INDEPENDENT OF INPUT VOLTAGE IF IT DOES NOT

EXCEED VALUES SHOWN

SINGLE Li-Ion CELL

(4.1V)

DOUBLE Li-Ion

CELL (8.2V)

16V

20V

BATTERY

VOLTAGE

Maximum Charging Current

, LTC and LT are registered trademarks of Linear Technology Corporation.

■

Charging of NiCd, NiMH, Lead-Acid or Lithium

Rechargeable Cells

■

Precision Current Limited Power Supply

■

Constant-Voltage/Constant-Current Supply

■

Transducer Excitation

■

Universal Input CCFL Driver

APPLICATIONS

Figure 1. SEPIC Charger with 1.25A Output Current

LT1513

L1A*

L1B*

1.25A

•

TAB4

GND

LT1513 • TA01

SYNC

AND/OR

SHUTDOWN

WALL

ADAPTER

INPUT

S/S

22µF

25V

C2**

4.7µF

0.1µF

†

L1A, L1B ARE TWO 10µH WINDINGS ON A

COMMON CORE: COILTRONICS CTX10-4

CERAMIC MARCON THCR40EIE475Z OR TOKIN 1E475ZY5U-C304

MBRD340 OR MBRS340T3. MBRD340 HAS 5µA TYPICAL

LEAKAGE, MBRS340T3 50

A TYPICAL

0.22µF

39Ω

270Ω

0.08Ω

22µF

25V

× 2

†

CHARGE

SHUTDOWN

TYPICAL APPLICATION

Summary of content (16 pages)

PAGE 1
LT1513/LT1513-2 SEPIC Constant- or Programmable-Current/ Constant-Voltage Battery Charger U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage Charges Any Number of Cells Up to 20V 1% Voltage Accuracy for Rechargeable Lithium Batteries 100mV Current Sense Voltage for High Efficiency (LT1513) 0mV Current Sense Voltage for Easy Current Programming (LT1513-2) Battery Can Be Directly Grounded 500kHz Switching Frequency Minimizes Inductor Siz
PAGE 2
LT1513/LT1513-2 W W W AXI U U ABSOLUTE RATI GS Supply Voltage ....................................................... 30V Switch Voltage ........................................................ 40V S/S Pin Voltage ....................................................... 30V FB Pin Voltage (Transient, 10ms) ......................... ±10V VFB Pin Current .................................................... 10mA IFB Pin Voltage (Transient, 10ms) .........................
PAGE 3
LT1513/LT1513-2 ELECTRICAL CHARACTERISTICS VIN = 5V, VC = 0.6V, VFB = VREF, IFB = 0V, VSW and S/S pins open, unless otherwise noted. SYMBOL PARAMETER MIN TYP MAX UNITS High Clamp, VFB = 1V Low Clamp, VFB = 1.5V 1.70 0.25 1.95 0.40 2.30 0.52 V V VC Pin Threshold Duty Cycle = 0% 0.8 1 1.25 V Switching Frequency 2.
PAGE 4
LT1513/LT1513-2 U W TYPICAL PERFORMANCE CHARACTERISTICS Switch Saturation Voltage vs Switch Current Switch Current Limit vs Duty Cycle 6 150°C 100°C 0.9 25°C SWITCH CURRENT LIMIT (A) 0.8 0.7 0.6 0.5 –55°C 0.4 0.3 0.2 3.0 5 2.8 25°C AND 125°C 4 INPUT VOLTAGE (V) 1.0 SWITCH SATURATION VOLTAGE (V) Minimum Input Voltage vs Temperature –55°C 3 2 2.6 2.4 2.2 2.0 1 0.1 0 0 0 0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.
PAGE 5
LT1513/LT1513-2 U U U PIN FUNCTIONS VC (Pin 1): The compensation pin is primarily used for frequency compensation, but it can also be used for soft starting and current limiting. It is the output of the error amplifier and the input of the current comparator. Peak switch current increases from 0A to 3.6A as the VC voltage varies from 1V to 1.9V. Current out of the VC pin is about 200µA when the pin is externally clamped below the internal 1.9V clamp level.
PAGE 6
LT1513/LT1513-2 W BLOCK DIAGRAM VIN SHUTDOWN DELAY AND RESET S/S SYNC SW LOW DROPOUT 2.3V REG 500kHz OSC ANTISAT LOGIC DRIVER SWITCH + 4k IFB IFBA – COMP 50k* – – + VFB + EA IA AV ≈ 6 VC 1.245V REF *REMOVE ON LT1513-2 0.04Ω – LT1513 • BD Figure 2 U OPERATION The LT1513 is a current mode switcher. This means that switch duty cycle is directly controlled by switch current rather than by output voltage or current.
PAGE 7
LT1513/LT1513-2 U W U U APPLICATIONS INFORMATION The LT1513 is an IC battery charger chip specifically optimized to use the SEPIC converter topology. A complete charger schematic is shown in Figure 1. The SEPIC topology has unique advantages for battery charging. It will operate with input voltages above, equal to or below the battery voltage, has no path for battery discharge when turned off, and eliminates the snubber losses of flyback designs.
PAGE 8
LT1513/LT1513-2 U W U U APPLICATIONS INFORMATION shown in the maximum charging current graph. Higher inductance values give slightly higher maximum charging current, but are larger and more expensive. A low loss toroid core such as Kool Mµ®, Molypermalloy or Metglas® is recommended. Series resistance should be less than 0.04Ω for each winding.
PAGE 9
LT1513/LT1513-2 U W U U APPLICATIONS INFORMATION vary depending on the mounting technique (copper area, airflow, etc.). current Schottky diodes have relatively high leakage currents (5µA to 500µA) even at room temperature. The latest very-low-forward devices have especially high leakage currents. It has been noted that surface mount versions of some Schottky diodes have as much as ten times the leakage of their through-hole counterparts.
PAGE 10
LT1513/LT1513-2 U U W U APPLICATIONS INFORMATION Programmed Charging Current exceed 60µA to maintain a sharp constant voltage to constant current crossover characteristic. ICHARGE can also be controlled by a PWM input. Assuming the signal is a CMOS rail-to-rail output with a source impedance of less than a few hundred ohms, effective ISET is VCC multiplied by the PWM ratio. ICHARGE has good linearity over the entire 0% to 100% range.
PAGE 11
LT1513/LT1513-2 U U W U APPLICATIONS INFORMATION problem, and indeed small signal loop stability can be excellent even in the presence of subharmonic switching. The primary issue with subharmonics is the presence of EMI at frequencies below 500kHz. (from the Electrical Characteristics). Amplifier output resistance is modeled with a 330k resistor. The power stage (modulator section) of the LT1513 is modeled as a transconductance whose value is 4(VIN)/(VIN + VBAT).
PAGE 12
LT1513/LT1513-2 U W U U APPLICATIONS INFORMATION The suggested way to control unity loop frequency is to increase the filter time constant on the IFB pin (R4/C4 in Figures 1 and 7). The filter resistor cannot be arbitrarily increased because high values will affect charging current accuracy. Charging current will increase by 1% for each 40Ω increase in R4.
PAGE 13
LT1513/LT1513-2 U TYPICAL APPLICATIONS Lithium-Ion Battery Charger with Switchable Charge Current (I )(R4) – IFBVOS ICHARGE = R5 R3 Many battery chemistries require several constant-current settings during the charging cycle. The circuit shown in Figure 8 uses the LT1513-2 to provide switchable 1.35A and 0.13A constant-current modes. The circuit is based on a standard SEPIC battery charger circuit set to a single lithium-ion cell charge voltage of 4.1V.
PAGE 14
LT1513/LT1513-2 U TYPICAL APPLICATIONS This Cold Cathode Fluorescent Lamp driver uses a Royer class self-oscillating sine wave converter to driver a high voltage lamp with an AC waveform. CCFL Royer converters have significantly degraded efficiency if they must operate at low input voltages, and this circuit was designed to handle input voltages as low as 2.7V.
PAGE 15
LT1513/LT1513-2 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. R Package 7-Lead Plastic DD Pak (LTC DWG # 05-08-1462) 0.060 (1.524) TYP 0.060 (1.524) 0.256 (6.502) 0.390 – 0.415 (9.906 – 10.541) 0.165 – 0.180 (4.191 – 4.572) 0.045 – 0.055 (1.143 – 1.397) 15° TYP 0.060 (1.524) 0.183 (4.648) 0.059 (1.499) TYP 0.330 – 0.370 (8.382 – 9.398) ( +0.203 0.102 –0.102 BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK ) 0.095 – 0.115 (2.413 – 2.
PAGE 16
LT1513/LT1513-2 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1239 Backup Battery Management System Charges Backup Battery and Regulates Backup Battery Output when Main Battery Removed LTC®1325 Microprocessor Controlled Battery Management System Can Charge, Discharge and Gas Gauge NiCd, NiMH and Pb-Acid Batteries with Software Charging Profiles LT1510 1.5A Constant-Current/Constant-Voltage Battery Charger Step-Down Charger for Li-Ion, NiCd and NiMH LT1511 3.