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LTC4070 Li-Ion/Polymer Shunt Battery Charger System FEATURES
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DESCRIPTION
The LTC(R)4070 allows simple charging of Li-Ion/Polymer batteries from very low current, intermittent or continuous charging sources. The 450nA to 50mA operating current makes charging possible from previously unusable sources. With the addition of an external pass device, shunt current may be boosted to 500mA. Stacked cell high voltage battery packs are inherently balanced with shunt charging. With its low operating current, the LTC4070 is well suited to charge thin film batteries in energy harvesting applications where charging sources may be intermittent or very low power. The unique architecture of the LTC4070 allows for an extremely simple battery charger solution; requiring just one external resistor. The LTC4070 offers a pin selectable float voltage with 1% accuracy across the full range of operating temperature and shunt current. The integrated thermal battery qualifier extends battery lifetime and improves reliability by automatically reducing the battery float voltage at NTC thermistor temperatures above 40C. The LTC4070 also provides both low and high battery status outputs. With the addition of an external PFET, the low-battery output pin can implement a latch-off function that automatically disconnects the system load from the battery to protect the battery from deep discharge. The device is offered in two thermally enhanced packages, a compact low profile (0.75mm) 8-lead (2mm x 3mm) DFN and an 8-lead MSOP package.
Low Operating Current (450nA) 1% Float Voltage Accuracy Over Full Temperature and Shunt Current Range 50mA Maximum Internal Shunt Current (500mA with External PFET) Pin Selectable Float Voltage Options: 4.0V, 4.1V, 4.2V Ultralow Power Pulsed NTC Float Conditioning for Li-Ion/Polymer Protection Suitable for Intermittent, Continuous and Very Low Power Charging Sources Low and High Battery Status Outputs Simple Low Voltage Load Disconnect Application Thermally Enhanced, Low Profile (0.75mm) 8-Lead (2mm x 3mm) DFN and MSOP Packages Low Power Li-Ion/Polymer Battery Back-Up Solar Power Systems with Back-Up Memory Back-Up Embedded Automotive Thin Film Batteries Energy Scavenging/Harvesting
APPLICATIONS
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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..
TYPICAL APPLICATION
VIN RIN
NTC Overtemperature Battery Float Voltage Qualifying
4.3 4.2 Q1:FDR8508 VF (V) 4.1 4.0 3.9 3.8 Li-Ion 3.7
0
Simple Shunt Charger with Load Disconnect and NTC Conditioning
ADJ = VCC ADJ = FLOAT ADJ = GND
VCC ADJ
LBO NTCBIAS 10k NTC
LTC4070
GND
T
+
20
NTHS0805E3103LT
40 60 TEMPERATURE (C)
80
100
4070 TA01b
4070 TA01a
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1
LTC4070 ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
ICC ....................................................................... 60mA ADJ, NTC, NTCBIAS, DRV, LBO, HBO Voltages .......................................... -0.3V to VCC + 0.3V Operating Junction Temperature Range.. -40C to 125C
Maximum Junction Temperature ......................... 125C Storage Temperature Range .................. -65C to 150C Peak Reflow Temperature ..................................... 260C
PIN CONFIGURATION
TOP VIEW TOP VIEW NTCBIAS 1 NTC 2 ADJ 3 HBO 4 9 8 7 6 5 VCC DRV LBO GND NTCBIAS NTC ADJ HBO 1 2 3 4 8 7 6 5 VCC DRV LBO GND
9
MS8E PACKAGE 8-LEAD PLASTIC MSOP DDB PACKAGE 8-LEAD (3mm 2mm) PLASTIC DFN TJMAX = 125C, JA = 76C/W EXPOSED PAD (PIN 9) IS NOT INTERNALLY CONNECTED, MUST BE SOLDERED TO PCB, GND TO OBTAIN JA TJMAX = 125C, JA = 40C/W EXPOSED PAD (PIN 9) IS NOT INTERNALLY CONNECTED, MUST BE SOLDERED TO PCB, GND TO OBTAIN JA
ORDER INFORMATION
LEAD FREE FINISH LTC4070EDDB#PBF LTC4070IDDB#PBF LTC4070EMS8E#PBF LTC4070IMS8E#PBF TAPE AND REEL LTC4070EDDB#TRPBF LTC4070IDDB#TRPBF LTC4070EMS8E#TRPBF LTC4070IMS8E#TRPBF PART MARKING* LFPD LFPD LTFMT LTFMT PACKAGE DESCRIPTION 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN 8-Lead Plastic MSOP 8-Lead Plastic MSOP TEMPERATURE RANGE -40C to 85C -40C to 125C -40C to 85C -40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
The l denotes the specifications which apply over the full operating junction temperature range. VNTC = VCC, TJ = 25C unless otherwise specified. Current into a pin is positive and current out of a pin is negative. All voltages are referenced to GND unless otherwise noted. (Note 2)
SYMBOL VFLOAT PARAMETER Programmable Float Voltage 10A ICC 50mA Maximum Shunt Current VCC Operating Current Low Bat VCC Operating Current CONDITIONS VADJ = 0V VADJ = Float VADJ = VCC VCC > VFLOAT VHBO Low VCC = 3.1V
l l l l l
ELECTRICAL CHARACTERISTICS
MIN 3.96 4.06 4.16 50
TYP 4.0 4.1 4.2 450 300
MAX 4.04 4.14 4.24 1040
UNITS V V V mA nA nA
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ICCMAX ICCQ ICCQLB
2
LTC4070 ELECTRICAL CHARACTERISTICS
SYMBOL VHBTH VHBHY VLBTH VLBHY VOL VOH PARAMETER HBO Threshold (VFLOAT - VCC) Hysteresis LBO Threshold Hysteresis CMOS Output Low CMOS Output High ISINK = 1mA, VCC = 3.7V VLBO: VCC = 3.1V, ISOURCE = -100A VHBO: ICC = 1.5mA, ISOURCE = -500A Input Logic Low Level Input Logic High Level IADJ(Z) NTC INTC INTCBIAS VFLOAT(NTC) NTC Leakage Current Average NTCBIAS Sink Current Delta Float Voltage per NTC Comparator Step 0V< NTC < VCC Pulsed Duty Cycle < 0.002% ICC = 1mA, NTC Falling Below One of the NTCTH Thresholds ADJ = 0V ADJ = Float ADJ = VCC VNTC as % of VNTCBIAS Amplitude 35.5 28.0 21.8 16.8 Hysteresis DRV Output Source Current DRV Output Sink Current VCC = 3.1V, VDRV = 0V ICC = 1mA, RDRV = 475k (Note 3) -50 0 30 50 nA pA Allowable ADJ Leakage Current in Floating State
l l
The l denotes the specifications which apply over the full operating junction temperature range. VNTC = VCC, TJ = 25C unless otherwise specified. Current into a pin is positive and current out of a pin is negative. All voltages are referenced to GND unless otherwise noted. (Note 2)
CONDITIONS VCC Rising
l
MIN 15
TYP 40 100
MAX 60
UNITS mV mV
High Battery Status
Low Battery Status VCC Falling
l
3.08 220
3.2 290
3.34 350 0.5
V mV V V
Status Outputs HBO/LBO VCC - 0.6
3-State Selection Input: ADJ VADJ ADJ Input Level
l l l
0.3 VCC - 0.3 3
V V A
-50 -75 -100 36.5 29.0 22.8 17.8 30 -1 3 37.5 30.0 23.8 18.8
mV mV mV % % % % mV mA A
NTCTH1 NTCTH2 NTCTH3 NTCTH4 NTCHY Drive Output IDRV(SOURCE) IDRV(SINK)
NTC Comparator Falling Thresholds
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC4070E is guaranteed to meet performance specifications for junction temperatures from 0C to 85C. Specifications over the -40C to 85C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC4070I is guaranteed over the full -40C to 125C operating junction temperature range. Note that the maximum ambient temperature is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors.
Note 3: The IDRV(SNK) current is tested by pulling the DRV pin up to VCC through a 475k resistor, RDRV. Pulling the DRV pin up to VCC with low impedance disables the regulator.
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LTC4070 TYPICAL PERFORMANCE CHARACTERISTICS
Battery Discharge ICC vs VCC
1000 900 800 700 VFLOAT (mV) ICC (nA) 600 500 400 300 200 100 0
0
TA = 25C, unless otherwise noted.
Load Regulation VFLOAT vs ICC
10 9 8 7 VFLOAT (V) 6 5 4 3 4.15 4.10 4.05 4.00 3.95
0
VFLOAT vs Temperature, ICC = 1mA
4.30 4.25 4.20 ADJ = VCC NO NTC
ADJ = GND
ADJ = FLOAT
FALLING RISING
ADJ = GND
2 1
1
2 VCC (V)
3
4
4070 G01
0 10 20 30 40 ICC (mA) 50 60
4070 G02
3.90 -50
-25
0 25 50 75 TEMPERATURE (C)
100
125
4070 G03
ICCQ vs Temperature (ADJ = VCC)
1000 900 800 700 ICCQ (nA) 600 500 400 300 200 100 0 -50 -25 0 25 50 75 TEMPERATURE (C) 100 125 VHBTH (mV) 100 90 80 70 60 50 40 30 20 10
VHBTH VCC Rising vs Temperature (ADJ = VCC)
300 250 200 VHBHY (mV) 150 100 50
VHBHY vs Temperature (ADJ = VCC)
0 -50
-25
0 25 50 75 TEMPERATURE (C)
100
125
0 -50
-25
0 25 50 75 TEMPERATURE (C)
100
125
4070 G04
4070 G05
4070 G06
VFLOAT vs NTC Temperature, ICC = 1mA
4.3 4.2 4.1 VFLOAT (V) 4.0 3.9 3.8 3.7
0
VLBTH VCC Falling vs Temperature
3.250 320 300 280 VLBHY (V) 260 3.245 3.240 ADJ = FLOAT
VLBHY vs Temperature
ADJ = VCC
ADJ = VCC ADJ = FLOAT ADJ = GND VLBTH (V)
3.235 3.230 3.225 3.220 3.215 3.210 3.205 ADJ = GND ADJ = VCC
ADJ = GND 240 220 200 -50 ADJ = FLOAT
20
60 40 TEMPERATURE (C)
80
100
4070 G07
3.200 -50
-25
0 25 50 75 TEMPERATURE (C)
100
125
-25
0 25 50 75 TEMPERATURE (C)
100
125
4070 G08
4070 G09
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LTC4070 TYPICAL PERFORMANCE CHARACTERISTICS
VOH LBO/HBO vs ISOURCE
2.5 2.5
TA = 25C, unless otherwise noted.
VOL LBO/HBO vs ISINK
VCC = 3.7V
2.0 VCC - VOH (V) LBO VCC = 3.1V VOL (V) 1.5 HBO VCC = VF - 25m
2.0
1.5
1.0
1.0
0.5
0.5
0
0
0 0.5 1.0 1.5 2.0 ISOURCE (mA) 2.5 3.0
4070 G10
0
2
4 6 ISINK (mA)
8
10
4070 G11
Power Spectral Density
35 30 25 20 15 10 5 0
0
Hot Plug Transient, CC = 330F , RIN = 81
CH4 = IIN (10mA/DIV) CH1 = VIN (2V/DIV)
Step Response with 800mAHr Battery, RIN = 81
CC = 10F ICC = 1mA, 1Hz Res , Bandwidth, Noise = 1.0452mVRMS from 10Hz to 100kHz
CH4 = IIN (10mA/DIV) CH1 = VIN (2V/DIV)
PSD (VRMS/Hz)
CH2 = VCC (2V/DIV) CH3 = VHBO (2V/DIV)
CH2 = VCC (2V/DIV) CH3 = VHBO (2V/DIV)
1
10 100 1000 10000 100000 FREQUENCY (Hz)
4070 G12
4ms/DIV
4070 G13
400ns/DIV
4070 G14
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LTC4070 PIN FUNCTIONS
NTCBIAS (Pin 1): NTC Bias Pin. Connect a resistor from NTCBIAS to NTC, and a thermistor from NTC to GND. Float NTCBIAS when not in use. Minimize parasitic capacitance on this pin. NTC (Pin 2): Input to the Negative Temperature Coefficient Thermistor Monitoring Circuit. The NTC pin connects to a negative temperature coefficient thermistor which is typically co-packaged with the battery to determine the temperature of the battery. If the battery temperature is too high, the float voltage is reduced. Connect a low drift bias resistor from NTCBIAS to NTC and a thermistor from NTC to GND. When not in use, connect NTC to VCC. Minimize parasitic capacitance on this pin. ADJ (Pin 3): Float Voltage Adjust Pin. Connect ADJ to GND to program 4.0V float voltage. Disconnect ADJ to program 4.1V float voltage. Connect ADJ to VCC to program 4.2V float voltage. The float voltage is also adjusted by the NTC thermistor. HBO (Pin 4): High Battery Monitor Output (Active High). HBO is a CMOS output that indicates that the battery is fully charged and current is being shunted away from BAT. This pin is driven high when VCC rises to within VHBTH of the effective float voltage. The absolute value of this threshold depends on ADJ and NTC, both of which affect the float voltage. HBO is driven low when VCC falls by more than (VHBTH + VHBHY) below the float voltage. Refer to Table 1 for the effective float voltage. GND (Pin 5, Exposed Pad Pin 9): Ground. The exposed package pad must be connected to PCB ground. LBO (Pin 6): Low Battery Monitor Output (Active High). LBO is a CMOS output that indicates when the battery is discharged below 3.2V or rises above 3.5V. This pin is driven high if VCC < VLBTH, and is driven low if VCC > (VLBTH + VLBHY). DRV (Pin 7): External Drive Output. Connect to the gate of an external PFET to increase shunt current for applications which require more than 50mA charge current. Minimize capacitance and leakage current on this pin. When not in use, float DRV. VCC (Pin 8): Input Supply Pin. The input supply voltage is regulated to 4.0V, 4.1V, or 4.2V depending on the ADJ pin state (see the ADJ pin description for more detail). This pin can sink up to 50mA in order to keep the voltage regulation within accuracy limits. When no battery is present, . decouple to GND with a capacitor, CIN, of at least 0.1F
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LTC4070 BLOCK DIAGRAM
LTC4070 VCC
ADJ PULSED DUTY CYCLE < 0.002% 30s CLK NTCBIAS
3-STATE DETECT
- +
LBO
1.5s
OSC
RNOM 10k NTC ADC T REF
+ -
HBO
+
EA
DRV
-
NTHS0805N02N1002J GND
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OPERATION
The LTC4070 provides a simple, reliable, and high performance battery protection and charging solution by preventing the battery voltage from exceeding a programmed level. Its shunt architecture requires just one resistor between the input supply and the battery to handle a wide range of battery applications. When the input supply is removed and the battery voltage is below the high battery output threshold, the LTC4070 consumes just 450nA from the battery. While the battery voltage is below the programmed float voltage, the charge rate is determined by the input voltage, the battery voltage, and the input resistor: ICHG = As the battery voltage approaches the float voltage, the LTC4070 shunts current away from the battery thereby reducing the charge current. The LTC4070 can shunt up to 50mA with float voltage accuracy of 1% over temperature. The shunt current limits the maximum charge current, but the 50mA internal capability can be increased by adding an external P-channel MOSFET. Adjustable Float Voltage, VFLOAT A built-in 3-state decoder connected to the ADJ pin provides three programmable float voltages: 4.0V, 4.1V, or 4.2V. The float voltage is programmed to 4.0V when ADJ is tied to GND, 4.1V when ADJ is floating, and 4.2V when ADJ is tied to VCC. The state of the ADJ pin is sampled about once every 1.5 seconds. When it is being sampled, the LTC4070 applies a relatively low impedance voltage at the ADJ pin. This technique prevents low level board leakage from corrupting the programmed float voltage.
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( VIN - VBAT )
RIN
7
LTC4070 OPERATION
NTC Qualified Float Voltage, VFLOAT(NTC) The NTC pin voltage is compared against an internal resistor divider tied to the NTCBIAS pin. This divider has tap points that are matched to the NTC thermistor resistance/temperature conversion table for a Vishay curve 2 type thermistor at temperatures of 40C, 50C, 60C, and 70C. The type #2 thermistor is also designated by a B25/85 value of 3490. Battery temperature conditioning adjusts the float voltage down to VFLOAT_EFF when the NTC thermistor indicates that the battery temperature is too high. For a 10k curve 2 thermistor and a 10k NTCBIAS resistor, each 10C increase in temperature above 40C causes the float voltage to drop by a fixed amount, VFLOAT(NTC), depending on ADJ. If ADJ is at GND, the float voltage steps down by 50mV for each 10C temperature increment. If ADJ is floating, the step size is 75mV. And if ADJ is at VCC, the step size is 100mV. Refer to Table 1 for the range of VFLOAT_EFF programming.
Table 1. NTC Qualified Float Voltage
ADJ VFLOAT(NTC) TEMPERATURE VNTC AS % OF NTCBIAS GND 50mV T < 40C VNTC > 36.5% 40C T < 50C 29.0% < VNTC 36.5% 50C T < 60C 22.8% < VNTC 29.0% 60C T < 70C 17.8% < VNTC 22.8% 70C < T VNTC 17.8% T < 40C VNTC > 36.5% 40C T < 50C 29.0% < VNTC 36.5% 50C T < 60C 22.8% < VNTC 29.0% 60C T < 70C 17.8% < VNTC 22.8% 70C T VNTC 17.8% VNTC > 36.5% T < 40C 40C T < 50C 29.0% < VNTC 36.5% 50C T < 60C 22.8%< VNTC 29.0% 60C T < 70C 17.8% < VNTC 22.8% 70C T VNTC 17.8% VFLOAT_
EFF
To conserve power in the NTCBIAS and NTC resistors, the NTCBIAS pin is sampled at a low duty cycle at the same time that the ADJ pin state is sampled. High Battery Status Output: HBO The HBO pin pulls high when VCC rises to within VHBTH of the programmed float voltage, VFLOAT_EFF, including NTC qualified float voltage adjustments. If VCC drops below the float voltage by more than VHBTH + VHBHY the HBO pin pulls low to indicate that the battery is not at full charge. The input supply current of the LTC4070 drops to less than 450nA (typ) as the LTC4070 no longer shunts current to protect the battery. The NTCBIAS sample clock slows to conserve power, and the DRV pin is pulled up to VCC. For example, if the NTC thermistor requires the float voltage to be dropped by 100mV (ADJ = VCC and 0.29*VNTCBIAS < VNTC < 0.36*VNTCBIAS) then the HBO rising threshold is detected when VCC rises past VFLOAT - VFLOAT(NTC) - VHBTH = 4.2V - 100mV - 40mV = 4.06V. The HBO falling threshold in this case is detected when VCC falls below VFLOAT - VFLOAT(NTC) - VHBTH - VHBHY = 4.2V - 100mV - 40mV - 100mV = 3.96V. Low Battery Status Output: LBO When the battery voltage drops below 3.2V, the LBO pin pulls high. Otherwise, the LBO pin pulls low when the battery voltage exceeds about 3.5V. While the low battery condition persists, NTC and ADJ pins are no longer sampled--the functions are disabled--and total supply consumption for the LTC4070 drops to less than 300nA (typ).
4.000V 3.950V 3.900V 3.850V 3.800V 4.100V 4.025V 3.950V 3.875V 3.800V 4.200V 4.100V 4.000V 3.900V 3.800V
Float
75mV
VCC
100mV
For all ADJ pin settings the lowest float voltage setting is 3.8V = VFLOAT - 4*VFLOAT(NTC) = VFLOAT_MIN. This occurs at NTC thermistor temperatures above 70C, or if the NTC pin is grounded.
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LTC4070 APPLICATIONS INFORMATION
General Charging Considerations The LTC4070 uses a different charging methodology from previous chargers. Most Li-Ion chargers terminate the charging after a period of time. The LTC4070 does not have a discrete charge termination. Extensive measurements on Li-Ion cells show that the cell charge current drops to nanoamps with the shunt charge control circuit effectively terminating the charge. For long cell life, operate the charger at 100mV lower charge voltage normally used. The simplest application of the LTC4070 is shown in Figure 1. This application requires only an external resistor to program the charge/shunt current. Assume the wall adapter voltage (VWALL) is 12V and the minimum battery voltage (VBAT_MIN) is 3V, then the maximum charge current is calculated as: IMAX _ CHARGE = = the programmed float voltage, the LTC4070 consumes only 450nA of current, and all of the input current flows into the battery. As the battery voltage reaches the float voltage, the LTC4070 shunts current from the wall adapter and regulates the battery voltage to VFLOAT. The more shunt current the LTC4070 sinks, the less charge current the battery gets. Eventually, the LTC4070 shunts all the current from the battery; up to the maximum shunt current. The maximum shunt current in this case, with no NTC adjustment, is determined by the input resistor and is calculated as:
ISHUNT _ MAX =
( VWALL - VFLOAT ) = (12V - 4.1V ) = 49mA
RIN 162
( VWALL - VBAT _ MIN )
RIN
At this point the power dissipated in the input resistor is 388mW. Figure 2 shows a charge circuit that can boost the charge current as well as the shunt current with an external P-channel MOSFET, Q1. In this case, if the wall adapter voltage (VWALL) is 24V and the minimum battery voltage (VBAT) is 3V, then the initial charge current is set to 191mA by selecting RIN = 110. Note that this resistor dissipates over 4W of power, so select the resistor taking power rating into account. When the battery voltage reaches the float voltage, the LTC4070 and the external P-channel MOSFET begin to shunt current from the wall adapter. Eventually, the LTC4070 and the external P-channel MOSFET shunts all available current (182mA) and no current flows to the battery. Take the full shunt current and power into account when selecting the external MOSFET.
RIN 110 4W NTC FLOAT IF NOT NEEDED LTC4070 NTCBIAS ADJ GND VCC DRV Q1
(12V - 3V )
162
= 55.5mA
Care must be taken in selecting the input resistor. Power dissipated in RIN under full charge current is given by the following equation: 2 VWALL - VBAT _ MIN (12V - 3V )2 PDISS = = = 0.5W RIN 162 The charge current decreases as the battery voltage increases. If the rising battery voltage is 40mV less than
(
)
12V WALL ADAPTER
RIN 162 0.5W NTC LTC4070 VCC
24V WALL ADAPTER
FLOAT IF NOT NEEDED FLOAT
NTCBIAS ADJ
+ Li-Ion
GND BATTERY
+ Li-Ion
BATTERY
4070 F01
Q1: FDN352AP
4070 F02
Figure 1. Single-Cell Battery Charger
Figure 2. Single-Cell Charger with Boosted Drive
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LTC4070 APPLICATIONS INFORMATION
The LTC4070 can also be used to regulate series-connected battery stacks as illustrated in Figures 3 and 4. Here two LTC4070 devices are used to charge two batteries in series; with or without boosted drive. A single resistor sets the maximum charge/shunt current. The GND pin of the top device is simply connected to the VCC pin of the bottom device. Care must be taken in observing the status output pins of the top device as these signals are not ground referenced. Also, the wall adapter must have a high enough voltage rating to charge both cells.
WALL ADAPTER RIN NTC LTC4070 FLOAT IF NOT NEEDED FLOAT NTCBIAS ADJ VCC1 VCC
NTC Protection The LTC4070 measures battery temperature with a negative temperature coefficient thermistor thermally coupled to the battery. NTC thermistors have temperature characteristics which are specified in resistance-temperature conversion tables. Internal NTC circuitry protects the battery from excessive heat by reducing the float voltage for each 10C rise in temperature above 40C (assuming a Vishay curve 2 thermistor). The LTC4070 uses a ratio of resistor values to measure battery temperature. The LTC4070 contains an internal fixed resistor voltage divider from NTCBIAS to GND with four tap points; NTCTH1-NTCTH4 . The voltages at these tap points are periodically compared against the voltage at the NTC pin to measure battery temperature. To conserve power, the battery temperature is measured periodically by biasing the NTCBIAS pin to VCC about once every 1.5 seconds. The voltage at the NTC pin depends on the ratio of the NTC thermistor value, RNTC, and a bias resistor, RNOM. Choose RNOM equal to the value of the thermistor at 25C. RNOM is 10k for a Vishay NTHSO402E3103LT curve 2 thermistor. RNOM must be connected from NTCBIAS to NTC. The ratio of the NTC pin voltage to the NTCBIAS voltage is: RNTC (RNTC + RNOM ) When the thermistor temperature rises, the resistance drops; and the resistor divider between RNOM and the thermistor lowers the voltage at the NTC pin.
+ Li-Ion
GND VCC2 NTC LTC4070 VCC BATTERY
FLOAT IF NOT NEEDED FLOAT
NTCBIAS ADJ
+ Li-Ion
GND BATTERY
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Figure 3. 2-Cell Battery Charger
WALL ADAPTER
RIN NTC
VCC1 VCC DRV Q1
FLOAT IF NOT NEEDED FLOAT
LTC4070 NTCBIAS ADJ
+ Li-Ion
GND VCC2 NTC VCC DRV Q2 BATTERY
FLOAT IF NOT NEEDED FLOAT
LTC4070 NTCBIAS ADJ
An NTC curve 1 thermistor may also be used with the LTC4070. However the temperature trip points are shifted due to the higher negative temperature coefficient of the curve 1 type thermistor. To correct for this difference add a resistor, RFIX, in series with the curve 1 thermistor to shift the ratio, RFIX + RNTC (RFIX + RNTC + RNOM ) up to the internal resistive divider tap points: NTCTH1 through NTCTH4. For a 100k curve 1 thermistor at 70C (with RNOM = 100k) choose RFIX = 3.92k. The temperature trip
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+ Li-Ion
GND BATTERY
Q1, Q2: Si3469DV
4070 F04
Figure 4. 2-Cell Battery Charger with Boosted Drive
10
LTC4070 APPLICATIONS INFORMATION
points are found by looking up the curve 1 thermistor R/T values plus RFIX that correspond to the ratios for NTCTH1 = 36.5%, NTCTH2 = 29.0%, NTCTH3 = 22.8%, and NTCTH4 = 17.8%. Selecting RFIX = 3.92k results in trip points of 39.9C, 49.4C, 59.2C and 69.6C. Another technique may be used without adding an additional component. Instead decrease RNOM to adjust the NTCTH thresholds for a given R/T thermistor profile. For example, if RNOM = 88.7k (with the same 100k curve 1 thermistor) then the temperature trip points are 41.0C, 49.8C, 58.5C, and 67.3C. When using the NTC features of the LTC4070 it is important to keep in mind that the maximum shunt current increases as the float voltage, VFLOAT_EFF drops with NTC conditioning. Reviewing the Typical Application with a 12V wall adapter in Figure 1; the input resistor, RIN, should be increased to 165 such that the maximum shunt current does not exceed 50mA at the lowest possible float voltage due to NTC conditioning, VFLOAT_MIN = 3.8V. Thermal Considerations At maximum shunt current, the LTC4070 may dissipate up to 205mW. The thermal dissipation of the package should be taken into account when operating at maximum shunt current so as not to exceed the absolute maximum junction temperature of the device. With JA of 40C/W, in the MSOP package, at maximum shunt current of 50mA the junction temperature rise is about 8C above ambient. With JA of 76C/W in the DFN package, at maximum shunt current of 50mA the junction temperature rise is about 16C above ambient. Operation with an External PFET To Boost Shunt Current Table 2 lists recommended devices to increase the maximum shunt current. Due to the requirement for low capacitance on the DRV pin node, it is recommended that only low gate charge and high threshold PFET devices be used. Also it is recommended that careful PCB layout be used to keep leakage at the DRV pin to a minimum as the IDRV(SINK) current is typically 3A. Refer to device manufacturers data sheets for maximum continuous power dissipation and thermal resistance when selecting an external PFET for a particular application.
Table 2. Recommended External Shunt PFETS
DEVICE FDN352AP Si3467DV Si3469DV DMP2130LDM DMP3015LSS VENDOR Fairchild Vishay Vishay Diodes Inc. Diodes Inc. QGS 0.50nC 1.7nC 3.8nC 2.0nC 7.2nC VTH(MIN) -0.8V -1.0V -1.0V -0.6V -1.0V RDS(ON) 0.33 0.073 0.041 0.094 0.014
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LTC4070 TYPICAL APPLICATIONS
DANGER! HIGH VOLTAGE! R3 249k R1 249k MB4S
AC 110
R4 249k
R2 249k
-
VCC NTC FLOAT IF NOT NEEDED LTC4070 NTCBIAS ADJ
+
+ Li-Ion
GND
4070 F05
VBE and VBC diodes of Q1. While the battery is charging, the majority of PV current flows to the battery. When VCC reaches the programmed float voltage, in this case 4.1V with ADJ floating, then the LTC4070 shunts base-collector junction current from Q1, effectively reducing the battery charging current to zero and saturating Q1. In the event that the thermistor temperature rises and the float voltage drops, the LTC4070 shunts more current, and Q1 is forced to operate in reverse active mode until the battery voltage falls. Once equilibrium is achieved, the difference between VBAT and VCC should be less than a few mV, depending on the magnitude of the shunt current. Add a series input resistor, RIN, to limit the current from high current solar cells. Solar cells are limited in current normally, so for small cells no resistor is needed. With high current PV cells, select RIN taking into account the PV cell's open-circuit voltage and short-circuit current, the temperature coefficient of the VBC and VBE diodes and the maximum collector current and operating junction temperature of Q1. Using an isolating transistor reduces discharge current to a few nanoamps, and may be extended to other applications as well. The PV application schematic in Figure 6 also illustrates using the LTC4070 with a 10k, 5% curve 2 type NTC thermistor, NTHS0402E3103LT. Here RNOM is 10k, and the rising temperature trip points are 40C, 50C, 60C and 70C.
VCC Q1 MP5650 VBAT OR 2N3904
BATTERY
DANGEROUS AND LETHAL POTENTIALS ARE PRESENT IN AC LINE-CONNECTED CIRCUITS! BEFORE PROCEEDING ANY FURTHER, THE READER IS WARNED THAT CAUTION MUST BE USED IN THE CONSTRUCTION, TESTING AND USE OF AC LINE-CONNECTED CIRCUITS. EXTREME CAUTION MUST BE USED IN WORKING WITH AND MAKING CONNECTIONS TO THESE CIRCUITS. ALL TESTING PERFORMED ON AN AC LINE-CONNECTED CIRCUIT MUST BE DONE WITH AN ISOLATION TRANSFORMER CONNECTED BETWEEN THE AC LINE AND THE CIRCUIT. USERS AND CONSTRUCTORS OF AC LINE-CONNECTED CIRCUITS MUST OBSERVE THIS PRECAUTION WHEN CONNECTING TEST EQUIPMENT TO THE CIRCUIT TO AVOID ELECTRIC SHOCK.
Figure 5. 4.2V AC Line Charging, UL Leakage Okay
The LTC4070 can be used to charge a battery to a 4.2V float voltage from an AC line with a bridge rectifier as shown in the simple schematic in Figure 5. In this example, the four input 249k resistors are sized for acceptable UL leakage in the event that one of the resistors short. Here, the LTC4070 will fully charge the battery from the AC line while meeting the UL specification with only 104A of available charge current. A photovoltaic (PV) application for the LTC4070 is illustrated in Figure 6. In this application, transistor Q1 has been added to further reduce the already low quiescent current of the LTC4070 to achieve extremely low battery discharge when the PV cells are not charging the battery. In long battery life applications, Q1 isolates the battery from the LTC4070 when Q1's base voltage falls. Under normal operation, the PV cells provide current through the
+ - + -
ADJ NTCBIAS CIN 0.1F LTC4070 NTC GND
FLOAT RNOM 10k
T
+
Li-Ion
RNTC: NTHS0402E3103LT 10k
4070 F06
Figure 6. Photovoltaic Charger with Extremely Low Leakage When Not Charging
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12
LTC4070 TYPICAL APPLICATIONS
The LTC4070 status pins have sufficient drive strength to use with an LED, for a visual indication of charging status. Consider the application in Figure 7, where red LED D1 is connected to the LBO pin and turns off when the battery voltage is below VLBTH. Note that LED D1 discharges the battery until VCC falls below VLBTH. Green LED D2, connected to the HBO pin turns on while the battery is charging. When the battery voltage rises to within VHBTH of the float voltage including NTC qualification, VFLOAT_EFF, D2 turns off to indicate that the battery is no longer charging. Optionally, a low leakage diode D3 is placed between the cathode of D2 and the battery. This diode stops D2 from discharging the battery when the input supply is not present. In this application, RIN = 205, is sized for a maximum shunt current of 50mA that occurs at the maximum input voltage of 15V and the minimum NTC qualified float voltage
VIN = 8V TO 15V RIN 205 1W OPTIONAL D3 BAS416 D1 LTST C190CKT VCC RLED2 1k RLED1 1k LTC4070 LBO HBO ADJ NTCBIAS RNOM 10k NTC GND T
of 3.8V, assuming the voltage drop on diode D3 is 1.1V. Without the optional D3, RIN increases to 226. Figure 8 illustrates an application to replace three NiMH cells with a single Li-Ion cell. This simple application replaces the NiMH charging solution without the need for a charge termination or cell balancing scheme. NiMH charging can be done without termination, but that algorithm limits the charge rate to C/10. The LTC4070 application allows the Li-Ion battery to be charged faster without concern of over-charging. Figure 9, 12V Wall Adapter Charging with 205mA, illustrates the use of an external PFET transistor to boost the maximum shunt current. If the battery voltage is 3.6V the battery receives the full charge current of about 205mA. If the battery temperature is below 40C, the float voltage rises to 4.1V (ADJ = floating) then Q1 and the LTC4070 shunts 192mA away from the battery. If the battery temperature rises, the shunt current increases to regulate the float voltage 75mV lower per 10C rise in battery temperature, as described in Table 1. At a maximum shunt current of 200mA the minimum float voltage is held at 3.8V when the battery temperature is above 70C. This example illustrates an alternative use of a LED, D1, to observe the HBO status pin. This LED turns on to provide a visual indication that the battery is fully charged, and shunts about 1.5mA when the battery rises to within 40mV of the desired float voltage. LED D1 discharges the battery, when no supply is present, until VCC falls by more than VHBTH + VHBHY below the float voltage. When using an LED with the HBO pin in this configuration, it is important to limit the LED current with a resistor, RLED as shown. Otherwise the step in current through RIN that occurs when the LED turns on may pull VCC below the HBO hysteresis. To prevent that situation, the ratio of RIN to RLED should be selected to meet the following relation: RIN ( V - V ) < VHBHY - 50mV RLED CC LED
VBAT = 4.1V
D2 LTST C190GKT
FLOAT
+
Li-Ion
4070 F07
RNTC: NTHS0402E3103LT 10k
Figure 7. Single Cell Charger with LED Status and NTC Qualified Float Voltage
IIN = 500mA
VBAT = 4.1V Q1 DMP3015LSS RNOM 10k
LTC4070
VCC
DRV
NTCBIAS LBO HBO ADJ NTC GND
FLOAT
T
+
Li-Ion
4070 TA01a
RNTC = NTHS0402E3103LT 10k
Figure 8. Replace Three NiMH with Lithium
where VLED is the forward voltage drop of the LED and a margin of 50mV is subtracted from the HBO hysteresis. A VLED value of 1.1V is assumed for this example. Refer to the LED data sheet for the forward voltage drop at the applied current level.
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13
LTC4070 PACKAGE DESCRIPTION
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 0.05 (2 SIDES) 0.70 0.05 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF
3.00 0.10 (2 SIDES)
R = 0.05 TYP 2.00 0.10 (2 SIDES) 0.56 0.05 (2 SIDES) 0.75 0.05
R = 0.115 TYP 5
0.40 0.10 8
4 0.25 0.05 2.15 0.05 (2 SIDES)
1 0.50 BSC
PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB8) DFN 0905 REV B
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
0 - 0.05
BOTTOM VIEW--EXPOSED PAD
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14
LTC4070 PACKAGE DESCRIPTION
MS8E Package 8-Lead Plastic MSOP Exposed Die Pad ,
(Reference LTC DWG # 05-08-1662 Rev E)
BOTTOM VIEW OF EXPOSED PAD OPTION 1 2.06 0.102 (.081 .004) 1.83 0.102 (.072 .004) 0.29 REF
2.794 (.110
0.102 .004)
0.889 (.035
0.127 .005)
0.05 REF 5.23 (.206) MIN 2.083 (.082
0.102 3.20 - 3.45 .004) (.126 - .136)
8
0.42 0.038 (.0165 .0015) TYP
0.65 (.0256) BSC
3.00 0.102 (.118 .004) (NOTE 3)
DETAIL "B" CORNER TAIL IS PART OF DETAIL "B" THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 0.52 (.0205) REF
8
7 65
RECOMMENDED SOLDER PAD LAYOUT
DETAIL "A" 0 - 6 TYP 4.90 0.152 (.193 .006) 3.00 0.102 (.118 .004) (NOTE 4)
0.254 (.010) GAUGE PLANE
1 0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE 0.22 - 0.38 (.009 - .015) TYP 1.10 (.043) MAX
23
4 0.86 (.034) REF
NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.65 (.0256) BSC
0.1016 (.004
0.0508 .002)
MSOP (MS8E) 0908 REV E
4070f
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC4070 TYPICAL APPLICATION
12V RIN 41.2 2W LTC4070 FLOAT SYSTEM STATUS ADJ HBO D1 LTST C190KGKT RLED 2.67k VCC LBO DRV NTCBIAS NTC GND T Q1: FDN352AP RNOM 10k Q2: FDR8508
+
Li-Ion
4070 TA02
RNTC: NTHS0402E3103LT 10k
Figure 9. 12V Wall Adapter Charging with 205mA with Automatic Load Disconnect on Low Battery
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Battery Chargers LTC1734L Lithium-Ion Linear Battery Charger in ThinSOT LTC4054L Standalone Linear Li-Ion Battery Charger in ThinSOT LTC4065L Standalone 250mA Li-Ion Battery Charger in 2mm x 2mm DFN ThinSOT is a trademark of Linear Technology Corporation.
4070f
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0110 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2010

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