Datasheet

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LT1512

1512fc

For more information www.linear.com/LT1512

Typical applicaTion

DescripTion

SEPIC Constant-Current/

Constant-Voltage Battery Charger

The LT

1512 is a 500kHz current mode switching regulator

specially conﬁgured to create a constant-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 switching and system

grounding problems. In addition, these topologies allow

charging even when the input voltage is lower than the

battery voltage.

Maximum switch current on the LT1512 is 1.5A. This allows

battery charging currents up to 1A 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.

Maximum Charging Current

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

All other trademarks are the property of their respective owners.

FeaTures

applicaTions

Battery Charging of NiCd, NiMH, Lead-Acid or

Lithium Rechargeable Cells

Precision Current Limited Power Supply

Constant-Voltage/Constant-Current Supply

Transducer Excitation

*Maximum Input Voltage = 40V – V

BAT

Charger Input Voltage May Be Higher, Equal to or

Lower Than Battery Voltage

Charges Any Number of Cells Up to 30V*

1% Voltage Accuracy for Rechargeable Lithium

Batteries

500kHz Switching Frequency Minimizes

Inductor Size

100mV Current Sense Voltage for High Efﬁciency

Battery Can Be Directly Grounded

Charging Current Easily Programmable or Shut Down

Figure 1. SEPIC Charger with 0.5A Output Current

LT1512

L1 A*

L1 B*

0.5A

•

GND GND S

1512 F01

SYNC

AND/OR

SHUTDOWN

WALL

ADAPTER

INPUT

S/S

22µF

25V

C2**

2.2µF

0.1µF

L1 A, L1 B ARE TWO 33µH WINDINGS ON A

SINGLE INDUCTOR: COILTRONICS CTX33-3

TOKIN CERAMIC 1E225ZY5U-C203-F

0.22µF

24Ω

CHARGE

SHUTDOWN

•

0.2Ω

22µF

25V

MBRS130LT3

ACTUAL PROGRAMMED CHARGING CURRENT WILL BE INDEPENDENT OF INPUT

VOLTAGE AND BATTERY VOLTAGE IF IT DOES NOT EXCEED THE VALUES SHOWN.

THESE ARE ELECTRICAL LIMITATIONS BASED ON MAXIMUM SWITCH CURRENT.

PACKAGE THERMAL LIMITATIONS MAY REDUCE MAXIMUM CHARGING CURRENT.

SEE APPLICATIONS INFORMATION.

INPUT VOLTAGE (V)

CURRENT (A)

0.6

0.8

1.0

1512 TA02

0.4

0.2

INDUCTOR = 33µH

DOUBLE

LITHIUM

CELL (8.2V)

6V BATTERY

12V BATTERY

SINGLE

LITHIUM

CELL (4.1V)

Summary of content (14 pages)

PAGE 1
LT1512 SEPIC Constant-Current/ Constant-Voltage Battery Charger Features n n n n n n n Description Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage Charges Any Number of Cells Up to 30V* 1% Voltage Accuracy for Rechargeable Lithium Batteries 500kHz Switching Frequency Minimizes Inductor Size 100mV Current Sense Voltage for High Efficiency Battery Can Be Directly Grounded Charging Current Easily Programmable or Shut Down The LT®1512 is a 500kHz current mode switching regulato
PAGE 2
LT1512 Absolute Maximum Ratings (Note 1) Pin Configuration Input 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
LT1512 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VC = 0.6V, VFB = VREF, IFB = 0V, VSW and S/S pins open, unless otherwise noted. SYMBOL PARAMETER CONDITIONS VIREF IFB Reference Voltage Measured at IFB Pin VFB = 0V, VC = 0.
PAGE 4
LT1512 Typical Performance Characteristics Switch Saturation Voltage vs Switch Current 3.0 0.7 0.6 –55°C 0.4 0.3 0.2 0.1 0 0 2.5 2.8 25°C AND 125°C 2.0 –55°C 1.5 1.0 0 FEEDBACK INPUT CURRENT (nA) MINIMUM SYNCHRONIZATION VOLTAGE (VP-P) 1.0 0.5 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1512 G04 4 700 VFB = VREF 600 500 400 300 200 100 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) Negative Feedback Input Current vs Temperature 800 1.
PAGE 5
LT1512 Pin Functions VC: 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 1.8A 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
LT1512 Block Diagram VIN SHUTDOWN DELAY AND RESET S/S SYNC SW LOW DROPOUT 2.3V REG 500kHz OSC ANTI-SAT LOGIC DRIVER SWITCH + IFB IFBA 5k – COMP 62k – – + FB 1.245V REF + EA IA VC AV ≈ 6 0.08Ω – GND 1512 F02 GND S Figure 2 6 1512fc For more information www.linear.
PAGE 7
LT1512 Operation The LT1512 is a current mode switcher. This means that switch duty cycle is directly controlled by switch current rather than by output voltage or current. Referring to the Block Diagram, the switch is turned “on” at the start of each oscillator cycle. It is turned “off” when switch current reaches a predetermined level. Control of output voltage and current is obtained by using the output of a dual feedback voltage sensing error amplifier to set switch current trip level.
PAGE 8
LT1512 Applications Information CONNECT D2 ANODE HERE FOR FULLY CHARGED BATTERY VOLTAGE LESS THAN 3.5V. Q1 WILL NOT BE TURNED OFF IN SHUTDOWN IF VIN IS PRESENT • CONNECT D2 ANODE HERE IF FULLY CHARGED BATTERY VOLTAGE IS GREATER THAN 3.5V AND Q1 MUST BE TURNED OFF IN SHUTDOWN WITH VIN STILL ACTIVE L1 A C2 VIN D1 VSW R1 SHUTDOWN S/S LT1512 GND R5 470k C6 470pF D2 1N4148 L1 B + Q1 2N7002 FB R3 R2 1512 F03 Figure 3.
PAGE 9
LT1512 Applications Information especially low. RMS ripple current in the input capacitor is less than 0.1A with L = 33µH and less than 0.2A with L = 15µH. A low ESR 22µF, 25V solid tantalum capacitor (AVX type TPS or Sprague type 593D) is adequate for most applications with the following caveat. Solid tantalum capacitors can be destroyed with a very high turn-on surge current such as would be generated if a low impedance input source were “hot switched” to the charger input.
PAGE 10
LT1512 Applications Information With ICHRG = 0.5A, VIN = 15V and VBAT = 8.2V, ICOUP = 0.43A The recommended capacitor is a 2.2µF ceramic type from Marcon or Tokin. These capacitors have extremely low ESR and high ripple current ratings in a small package. Solid tantalum units can be substituted if their ripple current rating is adequate, but typical values will increase to 22µF or more to meet the ripple current requirements.
PAGE 11
LT1512 Applications Information input to R5 is equal to the processor VCC level multiplied by the inverse PWM ratio. This assumes that the PWM signal is a CMOS output that swings rail-to-rail with a source resistance less than a few hundred ohms. The negative voltage is converted to a current by R5 and R6 and filtered by C7. This current multiplied by R4 generates a voltage that subtracts from the 100mV sense voltage of the LT1512.
PAGE 12
LT1512 Package Description Dimensions in inches (millimeters) unless otherwise noted. Package S88 Package 8-Lead Plastic Small Outline (Narrow 0.150) 8-Lead Plastic Small Outline (Narrow .150 Inch) (LTCLTC DWGDWG # 05-08-1610 Rev G) (Reference # 05-08-1610 Rev G) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN .160 ±.005 .010 – .020 × 45° (0.254 – 0.508) 2 .053 – .069 (1.346 – 1.752) 0°– 8° TYP .016 – .050 (0.406 – 1.270) .014 – .019 (0.355 – 0.
PAGE 13
LT1512 Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION B 6/14 Reconfigured inputs to LM301 PAGE NUMBER C 3/15 Changed inductor value units from “mH” to “µH” 14 1, 14 1512fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 14
LT1512 Typical Application The circuit in Figure 6 will provide adapter current limiting to ensure that the battery charger never overloads the adapter. In addition, it adjusts charging current to a lower value if other system power increases to the point where the adapter would be overloaded. This allows the WALL ADAPTER INPUT SYSTEM POWER R6 0.2Ω + + 3 2 – 4 D2 1N4148 VIN VSW 7 6 8 0.5A L1 B* LT1512 SYNC 4 AND/OR S/S SHUTDOWN GND GND S VC FB 2 IFB 1 C5 0.