LTC4070
1
4070fc
Typical applicaTion
DescripTion
Li-Ion/Polymer Shunt
Battery Charger System
The LTC
®
4070 allows simple charging of Li-Ion/Polymer
batteries from very low current, intermittent or continuous
charging sources. The 450nA to 50mA operating cur-
rent 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 quali-
fier extends battery lifetime and improves reliability by
automatically reducing the battery float voltage at NTC
thermistor temperatures above 40°C. The LTC4070 also
provides both low and high battery status outputs. For
applications requiring pack protection, see LTC4071.
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.
FeaTures
applicaTions
n Low Operating Current (450nA)
n 1% Float Voltage Accuracy Over Full Temperature
and Shunt Current Range
n 50mA Maximum Internal Shunt Current
(500mA with External PFET)
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 Low and High Battery Status Outputs
n Simple Low Voltage Load Disconnect Application
n Thermally Enhanced, Low Profile (0.75mm)
8-Lead (2mm × 3mm) DFN and MSOP Packages
n Low Power Li-Ion/Polymer Battery Back-Up
n Solar Power Systems with Back-Up
n Memory Back-Up
n Embedded Automotive
n Thin Film Batteries
n Energy Scavenging/Harvesting
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners..
NTC Overtemperature Battery Float
Voltage Qualifying
Simple Shunt Charger with Load Disconnect
and NTC Conditioning
TEMPERATURE (°C)
VF (V)
4.3
4.2
4.0
4.1
3.9
3.8
3.7 4020
0
60
4070 TA01b
80 100
ADJ = VCC
ADJ = FLOAT
ADJ = GND
4070 TA01a
LTC4070
ADJ
RIN
GND T
10k
Li-Ion
NTCBIAS
LBO
NTC
VCC
VIN
+
NTHS0805N02N1002F
Q1:FDR8508
LTC4070
2
4070fc
absoluTe MaxiMuM raTings
ICC ....................................................................... ±60mA
ADJ, NTC, NTCBIAS, DRV, LBO, HBO
Voltages ...........................................0.3V to VCC + 0.3V
Operating Junction Temperature Range .. 40°C to 125°C
(Notes 1, 2)
TOP VIEW
9
DDB PACKAGE
8-LEAD (3mm × 2mm) PLASTIC DFN
5
6
7
8
4
3
2
1NTCBIAS
NTC
ADJ
HBO
VCC
DRV
LBO
GND
TJMAX = 125°C, qJA = 76°C/W
EXPOSED PAD (PIN 9) IS NOT INTERNALLY CONNECTED,
MUST BE SOLDERED TO PCB, GND TO OBTAIN qJA
1
2
3
4
NTCBIAS
NTC
ADJ
HBO
8
7
6
5
VCC
DRV
LBO
GND
TOP VIEW
9
MS8E PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 125°C, qJA = 40°C/W
EXPOSED PAD (PIN 9) IS NOT INTERNALLY CONNECTED,
MUST BE SOLDERED TO PCB, GND TO OBTAIN qJA
pin conFiguraTion
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC4070EDDB#PBF LTC4070EDDB#TRPBF LFPD 8-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C
LTC4070IDDB#PBF LTC4070IDDB#TRPBF LFPD 8-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C
LTC4070EMS8E#PBF LTC4070EMS8E#TRPBF LTFMT 8-Lead Plastic MSOP –40°C to 125°C
LTC4070IMS8E#PBF LTC4070IMS8E#TRPBF LTFMT 8-Lead Plastic MSOP –40°C to 125°C
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/
Maximum Junction Temperature ......................... 125°C
Storage Temperature Range .................. 65°C to 150°C
Peak Reflow Temperature ..................................... 260°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VFLOAT Programmable Float Voltage
10µA ≤ ICC ≤ 50mA
VADJ = 0V
VADJ = Float
VADJ = VCC
l
l
l
3.96
4.06
4.16
4.0
4.1
4.2
4.04
4.14
4.24
V
V
V
ICCMAX Maximum Shunt Current VCC > VFLOAT l50 mA
ICCQ VCC Operating Current VHBO Low l450 1040 nA
ICCQLB Low Bat VCC Operating Current VCC = 3.1V 300 nA
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
junction temperature range. VNTC = VCC, TA = 25°C 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)
LTC4070
3
4070fc
elecTrical characTerisTics
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 LTC4070 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC4070E is guaranteed to meet performance specifications
for junction temperatures from 0°C to 85°C. Specifications over the
–40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The l denotes the specifications which apply over the full operating
junction temperature range. VNTC = VCC, TA = 25°C 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)
The LTC4070I is guaranteed over the full –40°C to 125°C operating
junction temperature range. Note that the maximum ambient temperature
consistent with these specifications 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.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
High Battery Status
VHBTH HBO Threshold (VFLOAT – VCC) VCC Rising l15 40 60 mV
VHBHY Hysteresis 100 mV
Low Battery Status
VLBTH LBO Threshold VCC Falling l3.08 3.2 3.34 V
VLBHY Hysteresis 220 290 350 mV
Status Outputs HBO/LBO
VOL CMOS Output Low ISINK = 1mA, VCC = 3.7V l0.5 V
VOH CMOS Output High VLBO: VCC = 3.1V, ISOURCE = –100µA
VHBO: ICC = 1.5mA, ISOURCE = –500µA
lVCC – 0.6 V
3-State Selection Input: ADJ
VADJ ADJ Input Level Input Logic Low Level l0.3 V
Input Logic High Level lVCC – 0.3 V
IADJ(Z) Allowable ADJ Leakage Current in
Floating State
l±3 µA
NTC
INTC NTC Leakage Current 0V< NTC < VCC –50 0 50 nA
INTCBIAS Average NTCBIAS Sink Current Pulsed Duty Cycle < 0.002% 30 pA
∆VFLOAT(NTC) Delta Float Voltage per NTC Comparator
Step
ICC = 1mA, NTC Falling Below One of the
NTCTH Thresholds
ADJ = 0V
ADJ = Float
ADJ = VCC
–50
–75
–100
mV
mV
mV
NTCTH1 NTC Comparator Falling Thresholds VNTC as % of VNTCBIAS Amplitude 35.5 36.5 37.5 %
NTCTH2 28.0 29.0 30.0 %
NTCTH3 21.8 22.8 23.8 %
NTCTH4 16.8 17.8 18.8 %
NTCHY Hysteresis 30 mV
Drive Output
IDRV(SOURCE) DRV Output Source Current VCC = 3.1V, VDRV = 0V –1 mA
IDRV(SINK) DRV Output Sink Current ICC = 1mA, RDRV = 475k (Note 3) 3 µA
LTC4070
4
4070fc
Typical perForMance characTerisTics
ICCQ vs Temperature (ADJ = VCC)
VHBTH VCC Rising vs Temperature
(ADJ = VCC)
VFLOAT vs Temperature, ICC = 1mA
VFLOAT vs NTC Temperature,
ICC = 1mA VLBTH VCC Falling vs Temperature VLBHY vs Temperature
Battery Discharge ICC vs VCC Load Regulation DVFLOAT vs ICC
TA = 25°C, unless otherwise noted.
VHBHY vs Temperature
(ADJ = VCC)
VCC (V)
ICC (nA)
1000
900
700
800
600
500
400
300
200
100
01
0
2
4070 G01
3 4
FALLING
ADJ = GND
RISING
ICC (mA)
VFLOAT (mV)
10
9
7
8
6
5
4
3
2
1
010
0
20 30
4070 G02
40 50 60
TEMPERATURE (°C)
VFLOAT (V)
4.30
4.25
4.15
4.20
4.10
4.05
4.00
3.95
3.90 –25
–50
25 500
4070 G03
75 100 125
ADJ = VCC
ADJ = FLOAT
ADJ = GND
NO NTC
TEMPERATURE (°C)
ICCQ (nA)
1000
900
700
800
600
500
400
300
200
100
0–25
–50
25 500
4070 G04
75 100 125
TEMPERATURE (°C)
VHBTH (mV)
100
90
70
80
60
50
40
30
20
10
0–25
–50
25 500
4070 G05
75 100 125
TEMPERATURE (°C)
VHBHY (mV)
300
250
150
200
100
50
0–25
–50
25 500
4070 G06
75 100 125
TEMPERATURE (°C)
VFLOAT (V)
4.3
4.2
4.0
4.1
3.9
3.8
3.7 4020
0
60
4070 G07
80 100
ADJ = VCC
ADJ = FLOAT
ADJ = GND
TEMPERATURE (°C)
VLBTH (V)
3.250
3.245
3.235
3.240
3.225
3.230
3.210
3.205
3.220
3.215
3.200 –25
–50
25 500
4070 G08
75 100 125
ADJ = FLOAT
ADJ = GND
ADJ = VCC
TEMPERATURE (°C)
VLBHY (V)
320
300
240
220
280
260
200 –25
–50
25 500
4070 G09
75 100 125
ADJ = FLOAT
ADJ = GND
ADJ = VCC
LTC4070
5
4070fc
Typical perForMance characTerisTics
Hot Plug Transient, CC = 330µF,
RIN = 81Ω
Step Response with 800mAHr
Battery, RIN = 81Ω
VOH LBO/HBO vs ISOURCE VOL LBO/HBO vs ISINK
Power Spectral Density
TA = 25°C, unless otherwise noted.
ISOURCE (mA)
VCC – VOH (V)
2.5
1.5
2.0
1.0
0.5
01.50.5 1.0
0
2.0
4070 G10
2.5 3.0
LBO
VCC = 3.1V
HBO
VCC = VF – 25m
ISINK (mA)
VOL (V)
2.5
1.5
2.0
1.0
0.5
042
0
6
4070 G11
8 10
VCC = 3.7V
4ms/DIV 4070 G13
CH1 = VIN
(2V/DIV)
CH2 = VCC
(2V/DIV)
CH3 = VHBO
(2V/DIV)
CH4 = IIN
(10mA/DIV)
400ns/DIV
CH1 = VIN (2V/DIV)
CH2 = VCC (2V/DIV)
CH3 = VHBO (2V/DIV)
CH4 = IIN (10mA/DIV)
4070 G14
FREQUENCY (Hz)
PSD (µVRMS/√Hz)
35
25
30
20
15
10
5
0101 100
0
1000 10000
4070 G12
100000
CC = 10µF, ICC = 1mA, 1Hz Res
Bandwidth, Noise = 1.0452mVRMS
from 10Hz to 100kHz
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.
LTC4070
6
4070fc
block DiagraM
pin FuncTions
4070 BD
3-STATE
DETECT
OSC
CLK
ADJ
1.5s
PULSED
DUTY CYCLE < 0.002%
30µs
NTCBIAS
NTC
RNOM
10k
T
+
+
REF
+
EA
GND
DRV
HBO
LBO
VCC
ADC
LTC4070
HBO (Pin 4): High Battery Monitor Output (Active High).
HBO is a CMOS output that indicates that the battery is
almost 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 for rated
thermal performance.
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 0.1µF.
LTC4070
7
4070fc
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 =V
IN VBAT
( )
R
IN
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.
NTC Qualified Float Voltage, DVFLOAT(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
thermistor with a B25/85 value of 3490 at temperatures of
40°C, 50°C, 60°C, and 70°C.
Battery temperature conditioning adjusts the float volt-
age down to VFLOAT_EFF when the NTC thermistor indi-
cates that the battery temperature is too high. For a 10k
thermistor with a B25/85 value of 3490 such as the Vishay
NTHS0402N02N1002F, and a 10k NTCBIAS resistor, each
10°C increase in temperature above 40°C causes the float
voltage to drop by a fixed amount, DVFLOAT(NTC), depend-
ing on ADJ. If ADJ is at GND, the float voltage steps down
by 50mV for each 10°C 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 DVFLOAT(NTC) TEMPERATURE VNTC AS % OF NTCBIAS
VFLOAT_
EFF
GND 50mV T < 40°C
40°C ≤ T < 50°C
50°C ≤ T < 60°C
60°C ≤ T < 70°C
70°C < T
VNTC > 36.5%
29.0% < VNTC ≤ 36.5%
22.8% < VNTC ≤ 29.0%
17.8% < VNTC ≤ 22.8%
VNTC ≤ 17.8%
4.000V
3.950V
3.900V
3.850V
3.800V
Float 75mV T < 40°C
40°C ≤ T < 50°C
50°C ≤ T < 60°C
60°C ≤ T < 70°C
70°C ≤ T
VNTC > 36.5%
29.0% < VNTC ≤ 36.5%
22.8% < VNTC ≤ 29.0%
17.8% < VNTC ≤ 22.8%
VNTC ≤ 17.8%
4.100V
4.025V
3.950V
3.875V
3.800V
VCC 100mV T < 40°C
40°C ≤ T < 50°C
50°C ≤ T < 60°C
60°C ≤ T < 70°C
70°C ≤ T
VNTC > 36.5%
29.0% < VNTC ≤ 36.5%
22.8%< VNTC ≤ 29.0%
17.8% < VNTC ≤ 22.8%
VNTC ≤ 17.8%
4.200V
4.100V
4.000V
3.900V
3.800V
For all ADJ pin settings the lowest float voltage setting is
3.8V = VFLOAT 4 DVFLOAT(NTC) = VFLOAT_MIN. This occurs
at NTC thermistor temperatures above 70°C, or if the NTC
pin is grounded.
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.
LTC4070
8
4070fc
operaTion
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 VFLOATDVFLOAT(NTC)
VHBTH = 4.2V – 100mV – 40mV = 4.06V. The HBO falling
threshold in this case is detected when VCC falls below
VFLOATDVFLOAT(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).
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 resis-
tor 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 cur-
rent is calculated as:
IMAX _ CHARGE =VWALL VBAT _ MIN
(
)
RIN
=12V 3V
(
)
162
Ω
=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:
PDISS =
VWALL VBAT _MIN
(
)
2
RIN
=12V 3V
(
)
2
162Ω=0.5W
The charge current decreases as the battery voltage
increases. If the rising battery voltage is 40mV less than
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
(
)
R
IN
=12V 4.1V
(
)
162Ω=49mA
At this point the power dissipated in the input resistor is
388mW.
Figure 1. Single-Cell Battery Charger
4070 F01
LTC4070
ADJ
RIN
162Ω
0.5W
GND
12V WALL
ADAPTER
Li-Ion
BATTERY
NTCBIAS
FLOAT
IF NOT NEEDED
FLOAT
NTC VCC
+
applicaTions inForMaTion
LTC4070
9
4070fc
applicaTions inForMaTion
Figure 3. 2-Cell Battery Charger
Figure 4. 2-Cell Battery Charger with Boosted Drive
LTC4070
ADJ
RIN
GND
WALL
ADAPTER
FLOAT
IF NOT NEEDED
FLOAT
FLOAT
IF NOT NEEDED
FLOAT
Li-Ion
BATTERY
NTCBIAS
NTC VCC
VCC1
+
4070 F03
LTC4070
ADJ GND
Li-Ion
BATTERY
NTCBIAS
NTC VCC
VCC2
+
LTC4070
ADJ
RIN
GND
WALL
ADAPTER
FLOAT
IF NOT NEEDED
FLOAT
FLOAT
IF NOT NEEDED
FLOAT
Li-Ion
BATTERY
NTCBIAS DRV Q1
NTC VCC
VCC1
VCC2
+
4070 F04
LTC4070
ADJ
GND
Li-Ion
BATTERY
NTCBIAS
Q1, Q2: Si3469DV
DRV Q2
NTC VCC
+
Figure 2. Single-Cell Charger with Boosted Drive
4070 F02
LTC4070
ADJ
Q1: FDN352AP
RIN
110Ω
4W
GND
24V WALL
ADAPTER
Li-Ion
BATTERY
NTCBIAS DRV Q1
NTC VCC
+
FLOAT
IF NOT NEEDED
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 = 110Ω. 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.
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 ref-
erenced. Also, the wall adapter must have a high enough
voltage rating to charge both cells.
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
10°C rise in temperature above 40°C (assuming a Vishay
thermistor with a B25/85 value of 3490).
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.
LTC4070
10
4070fc
applicaTions inForMaTion
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 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 is:
R
NTC
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 higher B25/85 values may also
be used with the LTC4070. 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 higher B25/85 value
thermistor to shift the ratio,
R
FIX +
R
NTC
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 NTHS0402N01N1003F, at 70°C (with RNOM =
100k) choose RFIX = 3.92kΩ. The temperature trip points
are found by looking up the 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 39.9°C,
49.4°C, 59.2°C and 69.6°C.
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 thermistor)
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 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 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 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 junc-
tion temperature of the device. With qJA 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 qJA of 76°C/W in the DFN package, at maximum
shunt current of 50mA the junction temperature rise is
about 16°C 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 3µA.
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 VENDOR QGS VTH(MIN) RDS(ON)
FDN352AP Fairchild 0.50nC –0.8V 0.33
Si3467DV Vishay 1.7nC –1.0V 0.073
Si3469DV Vishay 3.8nC –1.0V 0.041
DMP2130LDM Diodes Inc. 2.0nC –0.6V 0.094
DMP3015LSS Diodes Inc. 7.2nC –1.0V 0.014
LTC4070
11
4070fc
Typical applicaTions
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 104µA of
available charge current.
A photovoltaic (PV) application for the LTC4070 is illus-
trated 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
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, NTHS0402N02N1002F. Here RNOM is 10k,
and the rising temperature trip points are 40°C, 50°C,
60°C and 70°C.
Figure 6. Photovoltaic Charger with Extremely
Low Leakage When Not Charging
Figure 5. 4.2V AC Line Charging, UL Leakage Okay
FLOAT
IF NOT
NEEDED
4070 F05
LTC4070
AC 110
DANGER! HIGH VOLTAGE!
GND
NTCBIAS
MB4S
NTC
Li-Ion
BATTERY
VCC
R3
249k
R1
249k
ADJ
+
R4
249k
R2
249k
+
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.
4070 F06
LTC4070
ADJ
RNTC: NTHS0402N02N1002F 10k
GND
FLOAT
Q1
MP5650
T
RNOM
10k
Li-Ion
NTCBIAS
NTC
VCC VBAT
OR 2N3904
CIN
0.1µF
+
+
+
LTC4070
12
4070fc
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 = 205Ω, 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
Figure 7. Single Cell Charger with LED Status and
NTC Qualified Float Voltage
of 3.8V, assuming the voltage drop on diode D3 is 1.1V.
Without the optional D3, RIN increases to 226Ω.
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, il-
lustrates 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 40°C,
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 10°C 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 70°C.
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:
R
IN
RLED
VCC VLED
(
)
<VHBHY 50mV
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.
Figure 8. Replace Three NiMH with Lithium
4070 F07
LTC4070
ADJ
HBO
LBO
D1
LTST
C190CKT
OPTIONAL
D3
BAS416
VIN = 8V TO 15V
D2
LTST
C190GKT
RNTC: NTHS0402N02N1002F 10k
GND
FLOAT
T
RNOM
10k
Li-Ion
NTCBIAS
NTC
VCC
VBAT = 4.1V
RLED1
1k
RLED2
1k
RIN
205Ω
1W
+
4070 TA01a
LTC4070
ADJFLOAT
LBO
HBO
GND T
RNOM
10k
Li-Ion
NTCBIAS
DRV
NTC
VCC
IIN = 500mA
+
RNTC = NTHS0402N02N1002F 10k
VBAT = 4.1V
Q1
DMP3015LSS
LTC4070
13
4070fc
package DescripTion
DDB Package
8-Lead Plastic DFN (3mm ¥ 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
2.00 ±0.10
(2 SIDES)
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
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
0.56 ± 0.05
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
R = 0.05
TYP
2.15 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
14
85
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0 – 0.05
(DDB8) DFN 0905 REV B
0.25 ± 0.05
2.20 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.61 ±0.05
(2 SIDES)
1.15 ±0.05
0.70 ±0.05
2.55 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
0.50 BSC
LTC4070
14
4070fc
package DescripTion
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev E)
MSOP (MS8E) 0908 REV E
0.53 ± 0.152
(.021 ± .006)
SEATING
PLANE
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
0.18
(.007)
0.254
(.010)
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.86
(.034)
REF
0.65
(.0256)
BSC
0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
1 2 34
4.90 ± 0.152
(.193 ± .006)
8
8
1
BOTTOM VIEW OF
EXPOSED PAD OPTION
765
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
0.52
(.0205)
REF
1.83 ± 0.102
(.072 ± .004)
2.06 ± 0.102
(.081 ± .004)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
2.083 ± 0.102
(.082 ± .004)
2.794 ± 0.102
(.110 ± .004)
0.889 ± 0.127
(.035 ± .005)
RECOMMENDED SOLDER PAD LAYOUT
0.42 ± 0.038
(.0165 ± .0015)
TYP
0.65
(.0256)
BSC
0.1016 ± 0.0508
(.004 ± .002)
DETAIL “B”
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
0.05 REF
0.29
REF
LTC4070
15
4070fc
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
revision hisTory
REV DATE DESCRIPTION PAGE NUMBER
A 4/10 Change Q1’s Part Number on Figure 6 12
B 9/10 Updated Description section
Temperature Range updated in Order Information section
Updated Note 2
Text updated in “NTC Qualified Float Voltage, ∆VFLOAT(NTC)” section
Text updated in “NTC Protection” section
Updated Related Parts section
1
2
3
7
9, 10
16
C 4/11 Updated Vishay thermistor part number. 1, 7, 10, 11,
12, 16
LTC4070
16
4070fc
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
® LINEAR TECHNOLOGY CORPORATION 2010
LT 0411 REV C • PRINTED IN USA
relaTeD parTs
Typical applicaTion
PART NUMBER DESCRIPTION COMMENTS
Shunt Regulators
LT1389 Nanopower Precision Shunt Voltage Reference 800nA Operating Current, 0.05% Initial Accuracy, Low Drift: 10ppm/°C
LT1634 Micropower Precision Shunt Reference 10µA Operating Current, 0.05% Initial Accuracy, Low Drift: 10ppm/°C
Switching Regulators
LTC3588-1 Piezoelectric Energy Harvesting Power Supply
in 3mm × 3mm DFN and MSOP Packages High Efficiency Hysteretic Integrated Buck DC/DC; 950nA Input Quiescent Current
(Output in Regulation—No Load), 520nA Input Quiescent Current in UVLO, 2.6V to
19.2V Input Operating Range; Integrated Low-Loss Full-Wave Bridge Rectifier, Up to
100mA of Output Current, Selectable Output Voltages of 1.8V, 2.5V, 3.3V, 3.6V
LTC3620 Ultralow Power 15mA Step-Down Switching
Regulator in 2mm × 2mm DFN High Efficiency; Up to 95%, Maximum Current Output: 15mA, Externally
Programmable Frequency Clamp with Internal 50kHz Default Minimizes Audio Noise,
18µA IQ Current, 2.9V to 5.5 Input Voltage Range, Low-Battery Detection
LTC3642 High Efficiency High Voltage 50mA
Synchronous Step-Down Converter in
3mm × 3mm DFN and MSE Packages
Wide Input Voltage Range: 4.5V to 45V; Tolerant of 60V Input Transients, Internal
High Side and Low Side Power Switches; No Compensation Required, 50mA Output
Current, Low Dropout Operation: 100% Duty Cycle, Low Quiescent Current, 12µA
Battery Chargers
LTC1734L Lithium-Ion Linear Battery Charger in ThinSOT Low Current Version of LTC1734, 50mA ≤ ICHRG ≤ 180mA
LTC4054L Standalone Linear Li-Ion Battery Charger in
ThinSOT Low Current Version of LTC4054, 10mA ≤ ICHRG ≤ 150mA. Thermal Regulation
Prevents Overheating, C/10 Termination, with Integrated Pass Transistor
LTC4065L Standalone 250mA Li-Ion Battery Charger in
2mm × 2mm DFN Low Current Version of LTC4065, 15mA ≤ ICHRG ≤ 250mA, 4.2V, ±0.6% Float Voltage,
High Charge Current Accuracy: 5%
LTC4071 Li-Ion/Polymer Shunt Battery Charger System
with Low Battery Disconnect Charger Plus Pack Protection in One IC Low Operating Current (550nA), 50mA
Internal Shunt Current, Pin Selectable Float Voltages (4.0V, 4.1V, 4.2V), 8-lead,
2mm × 3mm, DFN and MSOP Packages
Figure 9. 12V Wall Adapter Charging with 205mA with
Automatic Load Disconnect on Low Battery
4070 TA02
LTC4070
12V
ADJ
HBO
RIN
41.2Ω
2W
RNTC: NTHS0402N02N1002F 10k
GND
FLOAT
SYSTEM
STATUS
T
RNOM
10k
Li-Ion
NTCBIAS
NTC
DRV
LBO
VCC
RLED
2.67k
D1
LTST
C190KGKT +
Q1: FDN352AP
Q2: FDR8508