LTC4070EDDB#PBF - LINEAR TECHNOLOGY

LTC4070

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

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

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

DDB PACKAGE

8-LEAD (3mm × 2mm) PLASTIC DFN

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

NTCBIAS

NTC

ADJ

HBO

VCC

DRV

LBO

GND

TOP VIEW

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

3.96

4.06

4.16

4.0

4.1

4.2

4.04

4.14

4.24

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

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

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

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

4070 G01

3 4

FALLING

ADJ = GND

RISING

ICC (mA)

∆VFLOAT (mV)

010

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

0–25

–50

25 500

4070 G05

75 100 125

TEMPERATURE (°C)

VHBHY (mV)

300

250

150

200

100

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

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

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

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

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)

0101 100

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

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

–

REF

–

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

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

( )

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

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 VFLOAT – DVFLOAT(NTC) –

VHBTH = 4.2V – 100mV – 40mV = 4.06V. The HBO falling

threshold in this case is detected when VCC falls below

VFLOAT – DVFLOAT(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

=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

(

)

RIN

=12V −3V

(

)

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

(

)

=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

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

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

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

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

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:

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,

FIX +

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

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

249k

ADJ

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

MP5650

RNOM

10k

Li-Ion

NTCBIAS

NTC

VCC VBAT

OR 2N3904

CIN

0.1µF

–

LTC4070

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:

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

LTST

C190CKT

OPTIONAL

BAS416

VIN = 8V TO 15V

LTST

C190GKT

RNTC: NTHS0402N02N1002F 10k

GND

FLOAT

RNOM

10k

Li-Ion

NTCBIAS

NTC

VCC

VBAT = 4.1V

RLED1

RLED2

RIN

205Ω

4070 TA01a

LTC4070

ADJFLOAT

LBO

HBO

GND T

RNOM

10k

Li-Ion

NTCBIAS

DRV

NTC

VCC

IIN = 500mA

RNTC = NTHS0402N02N1002F 10k

VBAT = 4.1V

DMP3015LSS

LTC4070

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)

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

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”

GAUGE PLANE

1 2 34

4.90 ± 0.152

(.193 ± .006)

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)

MS8E Package

8-Lead Plastic MSOP, Exposed Die Pad

(Reference LTC DWG # 05-08-1662 Rev E)

DETAIL “B”

CORNER TAIL IS PART OF

THE LEADFRAME FEATURE.

FOR REFERENCE ONLY

NO MEASUREMENT PURPOSE

0.05 REF

0.29

REF

LTC4070

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

9, 10

C 4/11 Updated Vishay thermistor part number. 1, 7, 10, 11,

12, 16

LTC4070

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

RNTC: NTHS0402N02N1002F 10k

GND

FLOAT

SYSTEM

STATUS

RNOM

10k

Li-Ion

NTCBIAS

NTC

DRV

LBO

VCC

RLED

2.67k

LTST

C190KGKT +

Q1: FDN352AP

Q2: FDR8508