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LTC4007

4007fc

TYPICAL APPLICATION

DESCRIPTION

4A, High Efﬁ ciency,

Standalone Li-Ion Battery Charger

The LTC

4007 is a complete constant-current/constant-

voltage charger controller for 3- or 4-cell lithium-ion batteries.

The PWM controller uses a synchronous, quasi-constant

frequency, constant off-time architecture that will not

generate audible noise even when using ceramic capacitors.

Charging current is programmable to ±4% accuracy using

a programming resistor. Charging current can also be

monitored as a voltage across the programming resistor.

The output ﬂ oat voltage is pin programmed for cell count

(3 cells or 4 cells) and chemistry (4.2V/4.1V). A timer,

programmed by an external resistor, sets the charge

termination time. Charging is automatically restarted when

cell voltage falls below 3.9V/cell.

LTC4007 includes a thermistor input, which suspends

charging if an unsafe temperature condition is detected.

If the cell voltage is less than 2.5V, a low-battery indicator

asserts and can be used to program a trickle charge current

to safely charge depleted batteries. The FAULT pin is also

asserted and charging terminates if the low-battery con-

dition persists for more than 1/4 of the total charge time.

12.6V, 4A Li-Ion Battery Charger

FEATURES

APPLICATIONS

n Complete Charger Controller for 3- or 4-Cell

Lithium-Ion Batteries

n High Conversion Efﬁ ciency: Up to 96%

n Output Currents Exceeding 4A

n ±0.8% Charging Voltage Accuracy

n Built-In Charge Termination for Li-Ion Batteries

n AC Adapter Current Limiting Maximizes Charge Rate*

n Thermistor Input for Temperature Qualiﬁ ed Charging

n Wide Input Voltage Range: 6V to 28V

n 0.5V Dropout Voltage; Maximum Duty Cycle: 98%

n Programmable Charge Current: ±4% Accuracy

n Indicator Outputs for Charging, C/10 Current Detection,

AC Adapter Present, Low Battery, Input Current

Limiting and Faults

n Charging Current Monitor Output

n Available in a 24-Pin Narrow SSOP Package

Notebook Computers

Portable Instruments

Battery-Backup Systems

Standalone Li-Ion Chargers

3C4C

CHEM

LOBAT

ACP

SHDN

FAULT

CHG

FLAG

NTC

LOBAT

ACP

SHDN

FAULT

CHG

FLAG

DCIN

INFET

CLP

CLN

TGATE

BGATE

PGND

CSP

BAT

PROG

ITH

GND

LTC4007

32.4k

309k

0.47μF

THERMISTOR

10k

NTC

TIMING RESISTOR

(~2 HOURS)

100k100k100k

LOGIC

DCIN

0V TO 28V

0.1μF

INPUT SWITCH

15nF

20μF

10μH

4.99k

3.01k

0.025Ω

20μF

Li-Ion

BATTERY

CHARGING

CURRENT

MONITOR

Q1: Si4431DY

Q2: FDC6459

SYSTEM

LOAD

0.12μF

6.04k

26.7k

0.0047μF

4007 TA01

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Protected by U.S. Patents including 5723970.

Summary of content (24 pages)

PAGE 1
LTC4007 4A, High Efficiency, Standalone Li-Ion Battery Charger FEATURES n n n n n n n n n n n n n DESCRIPTION Complete Charger Controller for 3- or 4-Cell Lithium-Ion Batteries High Conversion Efﬁciency: Up to 96% Output Currents Exceeding 4A ±0.8% Charging Voltage Accuracy Built-In Charge Termination for Li-Ion Batteries AC Adapter Current Limiting Maximizes Charge Rate* Thermistor Input for Temperature Qualiﬁed Charging Wide Input Voltage Range: 6V to 28V 0.
PAGE 2
LTC4007 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Voltage from DCIN, CLP, CLN to GND.......... +32V/–0.3V PGND with Respect to GND .................................. ±0.3V CSP, BAT to GND ......................................... +28V/–0.3V CHEM, 3C4C, RT to GND ................................ +7V/–0.3V NTC ............................................................. +10V/–0.3V ACP, SHDN, CHG, FLAG, FAULT, LOBAT, ICL ....................................... +32V/–0.3V CLP to CLN ..............
PAGE 3
LTC4007 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range (Note 4), otherwise speciﬁcations are at TA = 25°C. VDCIN = 20V, VBAT = 12V unless otherwise noted.
PAGE 4
LTC4007 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range (Note 4), otherwise speciﬁcations are at TA = 25°C. VDCIN = 20V, VBAT = 12V unless otherwise noted.
PAGE 5
LTC4007 TYPICAL PERFORMANCE CHARACTERISTICS INFET Response Time to Reverse Current Line Regulation Vgs OF PFET (2V/DIV) Vgs = 0 VOUT vs IOUT 0.10 0 0.05 –0.5 OUTPUT VOLTAGE ERROR (%) 0 Vs OF PFET (5V/DIV) VOUT ERROR (%) –0.05 C3C4 = OPEN –0.10 –0.15 –0.20 C3C4 = GND –0.25 –0.30 Vs = 0V –0.35 Id (REVERSE) OF PFET (5A/DIV) –0.45 –2.0 –2.5 –3.0 –3.5 –4.0 3C4C = GND 3C4C = OPEN –5.0 13 1.25μs/DIV –1.5 –4.5 –0.40 Id = 0A –1.0 TEST PERFORMED ON DEMOBOARD VCHARGE = 12.
PAGE 6
LTC4007 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency at 19VDC VIN Efﬁciency at 12.6V with 15VDC VIN 100 100 16.8V 95 95 EFFICIENCY (%) EFFICIENCY (%) 12.6V 90 85 80 90 85 80 75 75 0.50 1.00 1.50 2.00 2.50 CHARGE CURRENT (A) 3.00 4007 G10 0.50 1.00 1.50 2.00 2.50 CHARGE CURRENT (A) 3.00 4007 G11 PIN FUNCTIONS DCIN (Pin 1): External DC Power Source Input. Bypass this pin with at least 0.01μF. See Applications Information. CHG (Pin 2): Charge Status Output.
PAGE 7
LTC4007 PIN FUNCTIONS ITH (Pin 10): Control Signal of the Inner Loop of the Current Mode PWM. Higher ITH voltage corresponds to higher charging current in normal operation. A 6k resistor, in series with a capacitor of at least 0.1μF to GND provides loop compensation. Typical full-scale output current is 40μA. Nominal voltage range for this pin is 0V to 3V. PROG (Pin 11): Current Programming/Monitoring Input/ Output.
PAGE 8
LTC4007 BLOCK DIAGRAM 0.1μF VIN DCIN INFET Q3 1 5.8V 23 2 CHG CLN ACP 3 TIMER/CONTROLLER SHDN 24 OSCILLATOR 4 THERMISTOR 9 RRT RT FAULT 5 TBAD RESTART NTC 32.4k 10k NTC 0.47μF – FLAG 17 35mV + 6 – GND 397mV C/10 11.67μA 3C4C 7 MUX + CHEM 16 – 15 BAT – + RSENSE CA1 + 1.105V – + LOBAT 8 3k 14 CSP 20μF 3k 708mV gm = 1m Ω + 1.19V EA – 15nF CLN – 18 9k CL1 100mV 19 gm = 1.
PAGE 9
LTC4007 TEST CIRCUIT LTC4007 16 7 CHEM 3C4C 14 VREF + DIVIDER/ MUX EA – CSP 15 BAT 10 ITH + LT1055 – 0.6V 4007 TC OPERATION Overview The LTC4007 is a synchronous current mode PWM stepdown (buck) switcher battery charger controller. The charge current is programmed by the combination of a program resistor (RPROG) from the PROG pin to ground and a sense resistor (RSENSE) between the CSP and BAT pins. The ﬁnal ﬂoat voltage is programmed to one of four values (12.3V, 12.6V, 16.4V, 16.
PAGE 10
LTC4007 OPERATION Table 1.
PAGE 11
LTC4007 OPERATION The peak inductor current, at which ICMP resets the SR latch, is controlled by the voltage on ITH. ITH is in turn controlled by several loops, depending upon the situation at hand. The average current control loop converts the voltage between CSP and BAT to a representative current. Error amp CA2 compares this current against the desired current programmed by RPROG at the PROG pin and adjusts ITH until: VREF V – V + 11.67μA • 3.01kΩ = CSP BAT 3.01kΩ RPROG therefore, ⎛ V ⎞ 3.
PAGE 12
LTC4007 OPERATION by the timing resistor connected to RT, keeps switch S1 closed to sample the thermistor: tHOLD = 10 • RRT • 17.5pF = 54μs, for RRT = 309k tSAMPLE = 127.5 • 20 • RRT • 17.5pF = 13.8ms, When the tHOLD interval ends the result of the thermistor testing is stored in the D ﬂip-ﬂop (DFF). If the voltage at NTC is within the limits provided by the resistor divider feeding the comparators, then the NOR gate output will be low and the DFF will set TBAD to zero and charging will continue.
PAGE 13
LTC4007 APPLICATIONS INFORMATION Battery Detection LTC4007 It is generally not good practice to connect a battery while the charger is running. The timer is in an unknown state and the charger could provide a large surge current into the battery for a brief time. The Figure 5 circuit keeps the charger shut down and the timer reset while a battery is not connected. PROG 11 CPROG RPROG RZ 102k 5V 0V Q1 2N7002 4007 F06 LTC4007 1 DCIN ADAPTER POWER Figure 6.
PAGE 14
LTC4007 APPLICATIONS INFORMATION There are other effects to consider. The voltage across the current comparator is scaled to obtain the same values as the 100mV sense voltage target, but the input referred sense voltage is reduced, causing some careful consideration of the ripple current. Input referred maximum comparator threshold is 117mV, which is the same ratio of 1.4x the DC target. Input referred IREV threshold is scaled back to –24mV.
PAGE 15
LTC4007 APPLICATIONS INFORMATION be used when tantalum capacitors are used for input or output bypass. High input surge currents can be created when the adapter is hot-plugged to the charger or when a battery is connected to the charger. Solid tantalum capacitors have a known failure mechanism when subjected to very high turn-on surge currents. Kemet T495 series of “Surge Robust” low ESR tantalums are rated for high surge conditions such as battery to ground.
PAGE 16
LTC4007 APPLICATIONS INFORMATION Charger Switching Power MOSFET and Diode Selection Two external power MOSFETs must be selected for use with the charger: a P-channel MOSFET for the top (main) switch and an N-channel MOSFET for the bottom (synchronous) switch. The peak-to-peak gate drive levels are set internally. This voltage is typically 6V. Consequently, logic-level threshold MOSFETs must be used.
PAGE 17
LTC4007 APPLICATIONS INFORMATION Adapter Limiting An important feature of the LTC4007 is the ability to automatically adjust charging current to a level which avoids overloading the wall adapter. This allows the product to operate at the same time that batteries are being charged without complex load management algorithms. Additionally, batteries will automatically be charged at the maximum possible rate of which the adapter is capable.
PAGE 18
LTC4007 APPLICATIONS INFORMATION LTC4007 Example #2: 100kΩ NTC R9 NTC 9 C7 R9A RTH 4007 F10 Figure 10. General Thermistor Network If you are using a thermistor that doesn’t have a 1:7 HIGH/LOW ratio, or you wish to set the HIGH/LOW limits to different temperatures, then the more generic network in Figure 10 should work.
PAGE 19
LTC4007 APPLICATIONS INFORMATION Disabling the Thermistor Function If the thermistor is not needed, connecting a resistor between DCIN and NTC will disable it. The resistor should be sized to provide at least 10μA with the minimum voltage applied to DCIN and 10V at NTC. Do not exceed 30μA. Generally, a 301k resistor will work for DCIN less than 15V. A 499k resistor is recommended for DCIN between 15V and 24V. Conditioning Depleted Batteries Severely depleted batteries, with less than 2.
PAGE 20
LTC4007 APPLICATIONS INFORMATION General Rules 7. Connection of switching ground to system ground or internal ground plane should be single point. If the system has an internal system ground plane, a good way to do this is to cluster vias into a single star point to make the connection. 8. Route analog ground as a trace tied back to IC ground (analog ground pin if present) before connecting to any other ground. Avoid using the system ground plane.
PAGE 21
LTC4007 APPLICATIONS INFORMATION Q3 INPUT SWITCH DCIN 0V TO 20V 3A C1 0.1μF VLOGIC R10 100k R11 100k R12 100k * 3C4C DCIN * CHEM INFET LOBAT CLP LOBAT ICL ACP ACP TGATE SHDN SHDN BGATE FAULT FAULT PGND FLAG CHG R9 32.4k 1% THERMISTOR C7 0.47μF RT 309k 1% C2 20μF BAT Q2 D1 RSENSE 0.033Ω 1% C3 20μF R5 3.01k 1% ITH GND TIMING RESISTOR (~2 HOURS) L1 15μH 3A R4 3.01k 1% PROG RT Q1 SYSTEM LOAD BAT CSP FLAG NTC RCL 0.033Ω 1% C4 15nF LTC4007 CLN ICL CHG R1 4.
PAGE 22
LTC4007 APPLICATIONS INFORMATION SWITCH NODE DIRECTION OF CHARGING CURRENT L1 VBAT C2 VIN RSENSE HIGH FREQUENCY CIRCULATING PATH D1 C3 BAT 4007 F13 CSP BAT 4007 F12 Figure 12. High Speed Switching Path Figure 13. Kelvin Sensing of Charging Current PACKAGE DESCRIPTION GN Package 24-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .337 – .344* (8.560 – 8.738) 24 23 22 21 20 19 18 17 16 15 1413 .033 (0.838) REF .045 p.005 .229 – .244 (5.817 – 6.198) .254 MIN .150 – .
PAGE 23
LTC4007 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION B 7/10 Changed ±5% to ±4% in Description text 1 Updated Figure 6 13 C 8/10 PAGE NUMBER “Charge Termination” text added 1, 4, 6, 9, 10, 17 4007fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 24
LTC4007 TYPICAL APPLICATION 12.6V/4A Li-Ion Battery Charger Q3 INPUT SWITCH DCIN 0V TO 20V 3A C1 0.1μF VLOGIC R10 100k R11 100k R12 100k * LOBAT 3C4C DCIN CHEM INFET LOBAT CLP ICL ACP TGATE SHDN BGATE FAULT FAULT CHG R9 32.4k 1% FLAG C7 0.47μF RRT 309k 1% GND TIMING RESISTOR (~2 HOURS) D1 C3 20μF R4 3.01k 1% BAT ITH RSENSE L1 0.025Ω 10μH 4A 1% BAT Q2 R5 3.01k 1% PROG RT SYSTEM LOAD Q1 CSP NTC THERMISTOR 10k NTC RCL 0.