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PDF LTC4071 Data sheet ( Hoja de datos )
| Número de pieza | LTC4071 | |
| Descripción | Li-Ion/Polymer Shunt Battery Charger System | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC4071
Li-Ion/Polymer Shunt
Battery Charger System with
Low Battery Disconnect
Features
Description
n Charger Plus Pack Protection in One IC
n Low Operating Current (550nA)
n Near Zero Current (<0.1nA) Low Battery Disconnect
Function to Protect Batteries from Over-Discharge
n Pin Selectable Low Battery Disconnect Level:
2.7V or 3.2V
n 1% Float Voltage Accuracy Over Temperature
n 50mA Maximum Internal Shunt Current
n Pin Selectable Float Voltage Options: 4.0V, 4.1V, 4.2V
n Ultralow Power Pulsed NTC Float Conditioning for
Li-Ion/Polymer Protection
n Suitable for Intermittent, Continuous and Very Low
Power Charging Sources
n High Battery Status Output
n Thermally Enhanced, Low Profile (0.75mm)
8-Lead (2mm × 3mm) DFN and MSOP Packages
Applications
n Low Capacity, Li-Ion/Polymer Battery Back-Up
n Thin Film Batteries
n Energy Scavenging/Harvesting
n Solar Power Systems with Back-Up
n Memory Back-Up
n Embedded Automotive
The LTC®4071 allows simple charging of Li-Ion/Polymer
batteries from very low current, intermittent or continuous
charging sources. A near-zero current low battery latch-
ing disconnect function protects even the lowest capacity
batteries from deep discharge and potentially irreparable
damage. The 550nA to 50mA operating current makes
charging possible from previously unusable sources. With
its low operating current the LTC4071 is well suited to
charge low capacity Li-Ion or thin film batteries in energy
harvesting applications. The unique architecture of the
LTC4071 allows for an extremely simple battery charger
solution, requiring just one external resistor.
The LTC4071 offers a pin selectable float voltage with ±1%
accuracy. The integrated thermal battery qualifier extends
battery lifetime and improves reliability by automatically
reducing the battery float voltage at NTC thermistor tem-
peratures above 40°C. The LTC4071 also provides two
pin selectable low battery disconnect levels and a high
battery status output.
The device is offered in two thermally enhanced packages,
a compact low profile (0.75mm) 8-lead (2mm × 3mm)
DFN and an 8-lead MSOP package.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Typical Application
VIN
RIN TO SYSTEM LOAD: VCC
ADJ
NTC
1µF
VCC BAT
LTC4071
LBSEL GND
+
Li-Ion
4071 TA01a
Battery Disconnect ILEAK vs Temperature
100n VBAT = 2.65V
10n
1n
100p
10p
1p
0.1p
–25
0
25 50 75 100 125
TEMPERATURE (°C)
4071 TA01b
4071fc
1
1 page  
LTC4071
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
MP1 Body Diode
1.0
0.9
VCC = 3.5V
LBSEL = GND
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.01
0.1 1
IBAT (mA)
125°C
85°C
25°C
–45°C
10 100
4071 G10
HBO VOH
2000
1800
LBSEL = VCC
NTC = NTCBIAS
1600
1400
ADJ = GND
1200
1000
ADJ = VCC
800
600
400
200
0
0 0.5 1 1.5 2 2.5
ISOURCE (mA)
4071 G11
HBO VOL
1200
LBSEL = VCC
NTC = NTCBIAS
900
600
300
VCC = 3.6V
VCC = 4.0V
0
0123456
ISINK (mA)
4071 G12
LBSEL VIL / VIH vs Temperature
1400
1200
1000
VIH
800
600 VIL
400
200
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4071 G13
NTCBIAS Pulse Width
vs Temperature
250
200
150
HBO LOW
100
50 HBO HIGH
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4071 G15
VF vs NTC Temperature
4.25
4.20 ADJ = VCC
4.15
4.10 ADJ = FLOAT
4.05
4.00 ADJ = GND
3.95
3.90
3.85
3.80
3.75
LBSEL = VCC
0 20 40 60 80
NTC TEMPERATURE (°C)
100
4071 G14
NTCBIAS Period vs Temperature
7
6
5
4 HBO LOW
3
2
HBO HIGH
1
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4071 G16
4071fc
5
5 Page 
LTC4071
Applications Information
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 HBO status output pin of the top device as
this signal is no longer ground referenced. Likewise for
the control inputs of the top device; tie ADJ and LBSEL
of the top device to the local GND or VCC pins. Also, the
wall adapter must have a high enough voltage rating to
charge both cells.
NTC Protection
The LTC4071 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
10°C rise in temperature above 40°C (assuming a Vishay
thermistor with a B25/85 value of 3490).
The LTC4071 uses a ratio of resistor values to measure
battery temperature. The LTC4071 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 NTC
thermistor value, RNTC, and a bias resistor, RNOM. Choose
RNOM equal to the value of the thermistor at 25°C. RNOM
is 10k for a Vishay NTHS0402N02N1002F thermistor with
a B25/85 value of 3490. RNOM must be connected from
NTCBIAS to NTC. The ratio of the NTC pin voltage to the
NTCBIAS voltage when it is pulsed to VCC 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.
An NTC thermistor with a different B25/85 value may also
be used with the LTC4071. However the temperature trip
points are shifted due to the higher negative temperature
coefficient of the thermistor. To correct for this difference
add a resistor, RFIX, in series with the thermistor to shift
the ratio:
RFIX + RNTC
( ) RFIX + RNTC + RNOM
Up to the internal resistive divider tap points: NTCTH1
through NTCTH4. For a 100k thermistor with a B25/85
value of 3950, e.g. NTHS0402N01N1003F, at 70°C (with
RNOM = 100k) choose RFIX = 3.92k. The temperature trip
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%, NTCTH3 = 22.8%, and NTCTH4
= 17.8%. Selecting RFIX = 3.92k results in trip points of
39.9°C, 49.4°C, 59.2°C and 69.6°C.
Another technique may be used without adding an ad-
ditional 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 thermis-
tor) then the temperature trip points are 41.0°C, 49.8°C,
58.5°C and 67.3°C.
When using the NTC features of the LTC4071 it is important
to keep in mind that the maximum shunt current increases
asthefloatvoltage,VFLOAT_EFF dropswithNTC conditioning.
Reviewing the single-cell battery charger application with
a 12V wall adapter in Figure 2; the input resistor should be
increased to 165Ω 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 LTC4071 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 junc-
tion temperature of the device. With θJA of 40°C/W, in the
MSOP package, at maximum shunt current of 50mA the
junction temperature rise is about 8°C above ambient.
With θJA of 76°C/W in the DFN package, at maximum
shunt current of 50mA the junction temperature rise is
about 16°C above ambient. The junction temperature, TJ,
is calculated depending on ambient temperature, TA, power
4071fc
11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LTC4071.PDF ] | |
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