LTC4011EFE#PBF - Linear Technology Corporation

LTC4011

4011p

, LTC and LT are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

High Efficiency Standalone

Nickel Battery Charger

■

Complete NiMH/NiCd Charger for 1 to 16 Cells

■

No Microcontroller or Firmware Required

■

550kHz Synchronous PWM Current Source Controller

■

No Audible Noise with Ceramic Capacitors

■

PowerPath

Control Support

■

Programmable Charge Current: 5% Accuracy

■

Wide Input Voltage Range: 4.5V to 34V

■

Automatic Trickle Precharge

■

–∆V Fast Charge Termination

■

Optional ∆T/∆t Fast Charge Termination

■

Automatic NiMH Top-Off Charge

■

Programmable Timer

■

Automatic Recharge

■

Multiple Status Outputs

■

Micropower Shutdown

■

20-Lead Thermally Enhanced TSSOP Package

■

Integrated or Standalone Battery Charger

■

Portable Instruments or Consumer Products

■

Battery-Powered Diagnostics and Control

■

Back-Up Battery Management

PowerPath is a trademark of Linear Technology Corporation.

The LTC

4011 provides a complete, cost-effective nickel

battery fast charge solution in a small package using few

external components. A 550kHz PWM current source

controller and all necessary charge initiation, monitoring

and termination control circuitry are included.

The LTC4011 automatically senses the presence of a DC

adapter and battery insertion or removal. Heavily dis-

charged batteries are precharged with a trickle current.

The LTC4011 can simultaneously use both –∆V and ∆T/∆t

fast charge termination techniques and can detect various

battery faults. If necessary, a top-off charge is automati-

cally applied to NiMH batteries after fast charging is

completed. The IC will also resume charging if the battery

self-discharges after a full charge cycle.

All LTC4011 charging operations are qualified by actual

charge time and maximum average cell voltage. Charging

may also be gated by minimum and maximum tempera-

ture limits. NiMH or NiCd fast charge termination param-

eters are pin-selectable.

Integrated PowerPath control support ensures that the

system remains powered at all times without allowing load

transients to adversely affect charge termination.

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

INFET

FAULT

CHRG

TOC

READY

VCC

TGATE

VCDIV

VCELL

VTEMP

LTC4011

DCIN

TIMER

GND

CHEM

VRT

INTVDD

SENSE

BAT

FROM

ADAPTER

4.5V TO 34V

10µH

10µF

SYSTEM

LOAD

0.05Ω

2-CELL

NiMH PACK

WITH 10k NTC

(2AHr)

4011 TA01a

20k

49.9k

10k 10k

10.7k

0.1µF0.033µF0.068µF

10µF

30.9k

BGATE

PGND

2A NiMH Battery Charger

TIME (MINUTES)

1.25

CELL VOLTAGE (V)

BATTERY TEMPERATURE (°C)

1.30

1.40

1.45

1.50

1.60

4011 TA01b

1.35

1.55

40 100

20 60 80

SINGLE CELL

VOLTAGE

CHARGE

CURRRENT

BATTERY

TEMPERATURE

TOP OFF

Typical NiMH Charge Cycle at 1C

Electrical Specifications Subject to Change

LTC4011

4011p

ORDER PART

NUMBER

(Note 1)

(Input Supply) to GND ....................... –0.3V to 40V

DCIN to GND ............................................ –0.3V to 40V

FAULT, CHRG, V

CELL

, V

CDIV

, BAT, TOC

or READY to GND .......................... –0.3V to V

+ 0.3V

SENSE to BAT ...................................................... ±0.3V

CHEM, V

TEMP

or TIMER to GND .............. –0.3V to 3.5V

PGND to GND ...................................................... ±0.3V

Operating Ambient Temperature Range

(Note 2) .................................................. – 40°C to 85°C

Operating Junction Temperature (Note 3) ........... 125°C

Storage Temperature Range ................. – 65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

LTC4011EFE

JMAX

= 125°C, θ

= 38°C/W

EXPOSED PAD (PIN 21) IS GND. MUST BE SOLDERED TO

PCB TO OBTAIN SPECIFIED THERMAL RESISTANCE

ABSOLUTE MAXIMUM RATINGS

PACKAGE/ORDER INFORMATION

The ● indicates specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

FE PACKAGE

20-LEAD PLASTIC TSSOP

TOP VIEW

DCIN

FAULT

CHRG

CHEM

GND

TEMP

CELL

CDIV

TIMER

INFET

READY

TGATE

PGND

BGATE

INTV

TOC

BAT

SENSE

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Supply

Input Voltage Range ●4.5 34 V

SHDN

Shutdown Quiescent Current (Note 5) V

= BAT = 4.8V 5 10 µA

Quiescent Current Waiting to Charge (Pause) ●35mA

Operating Current Fast Charge State, No Gate Load ●59mA

UVLO

Undervoltage Threshold Voltage V

Increasing ●3.95 4.2 4.45 V

UV(HYST)

Undervoltage Hysteresis Voltage 170 mV

SHDNI

Shutdown Threshold Voltage DCIN – V

, DCIN Increasing ●20 30 42 mV

SHDND

Shutdown Threshold Voltage DCIN – V

, DCIN Decreasing ●–45 –25 –15 mV

Charge Enable Threshold Voltage V

– BAT, V

Increasing ●400 510 600 mV

INTV

Regulator

Output Voltage No Load ●4.5 5 5.5 V

Short-Circuit Current (Note 6) INTV

= 0V ●–100 –50 –28 mA

INTV

DD(MIN)

Output Voltage V

= 4.5V, I

= –10mA ●3.85 V

Thermistor Termination

Output Voltage R

= 10k 3.125 3.3 3.475 V

●3.05 3.55 V

Short-Circuit Current V

= 0V ●–9 –1 mA

PWM Current Source

BAT – SENSE Full-Scale Regulation 0.3V < BAT < V

– 0.3V (Note 5) 95 100 105 mV

Voltage (Fast Charge) BAT = 4.8V ●95 100 105 mV

BAT – SENSE Precharge Regulation 0.3V < BAT < V

– 0.3V (Note 5) 16 20 24 mV

Voltage BAT = 4.8V ●16 20 24 mV

LTC4011

4011p

The ● indicates specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

BAT – SENSE Top-Off Charge 0.3V < BAT < V

– 0.3V (Note 5) 6.5 10 13.5 mV

Regulation Voltage BAT = 4.8V ●6.5 10 13.5 mV

∆V

BAT – SENSE Line Regulation 5.5V < V

< 34V, Fast Charge ±0.3 mV

BAT

BAT Input Bias Current 0.3V < BAT < V

– 0.1V –2 2 mA

SENSE

SENSE Input Bias Current SENSE = BAT 50 150 µA

OFF

Input Bias Current SENSE or BAT, V

CELL

= 0V ●–1 0 1 µA

TYP

Typical Switching Frequency ●460 550 615 kHz

MIN

Minimum Switching Frequency ●20 30 kHz

MAX

Maximum Duty Cycle 98 99 %

OL(TG)

TGATE Output Voltage Low V

> 9V, No Load ●5 5.6 8.75 V

– TGATE, Note 7) V

< 7.5V, No Load ●V

–V

0.5

OH(TG)

TGATE Output Voltage High V

– TGATE, No Load ●050mV

R(TG)

TGATE Rise Time C

LOAD

= 3nF, 10% to 90% 35 100 ns

F(TG)

TGATE Fall Time C

LOAD

= 3nF, 10% to 90% 45 100 ns

OL(BG)

BGATE Output Voltage Low No Load ●050mV

OH(BG)

BGATE Output Voltage High No Load ●INTV

INTV

– 0.075

R(BG)

BGATE Rise Time C

LOAD

= 1.6nF, 10% to 90% 35 65 ns

F(BG)

BGATE Fall Time C

LOAD

= 1.6nF, 10% to 90% 15 65 ns

ADC Inputs

LEAK

Analog Channel Leakage 0V < V

CELL

< 2V, 550mV < V

TEMP

< 2V ±100 nA

Charger Thresholds

Battery Present Threshold Voltage ●320 350 370 mV

BOV

Battery Overvoltage ●1.85 1.95 2.05 V

MFC

Minimum Fast Charge Voltage ●850 900 950 mV

FCBF

Fast Charge Battery Fault Voltage ●1.17 1.22 1.27 V

∆V

TERM

–∆V Termination CHEM = 3.3V (NiCd) ●16 20 25 mV

CHEM = 0V (NiMH) ●61014mV

Automatic Recharge Voltage V

CELL

Decreasing ●1.275 1.325 1.375 V

∆T

TERM

∆T Termination (Note 8) CHEM = 3.3 (NiCd) ●1.3 2 2.7 °C/min

CHEM = 0V (NiMH) ●0.5 1 1.5 °C/min

MIN

Minimum Charging Temperature V

TEMP

Increasing ●0.5 5 8.5 °C

(Note 8)

MAXI

Maximum Charge Initiation V

TEMP

Decreasing, Not Charging ●41.5 45 47 °C

Temperature (Note 8)

MAXC

Maximum Fast Charge Temperature V

TEMP

Decreasing, Fast Charge ●57 60 63 °C

(Note 8)

TEMP(D)

TEMP

Disable Threshold Voltage ●2.8 3.3 V

TEMP(P)

Pause Threshold Voltage ●130 280 mV

Charger Timing

∆t

TIMER

Internal Time Base Error ●–10 10 %

∆t

MAX

Programmable Timer Error R

TIMER

= 49.9k ●–20 20 %

LTC4011

4011p

The ● indicates specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

PowerPath Control

INFET Forward Regulator Voltage DCIN – V

●30 55 100 mV

OL(INFET)

Output Voltage Low V

– INFET, No Load ●3.75 5.2 7 V

OH(INFET)

Output Voltage High V

– INFET, No Load ●050mV

OFF(INFET)

INFET OFF Delay Time C

LOAD

= 10nF, INFET to 50% 3 15 µs

Status and Chemistry Select

Output Voltage Low (I

LOAD

= 10mA) V

CDIV

●435 700 mV

All Other Status Outputs ●300 600 mV

LKG

Output Leakage Current All Status Outputs Inactive, V

OUT

= V

●–10 10 µA

IH(VCDIV)

Input Current High V

CDIV

= V

BAT

(Shutdown) ●–1 1 µA

Input Voltage Low CHEM (NiMH) ●900 mV

Input Voltage High CHEM (NiCd) ●2.85 V

Input Current Low CHEM = GND ●–20 –5 µA

Input Current High CHEM = 3.3V ●–20 20 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life

of the device may be impaired.

Note 2: The LTC4011E is guaranteed to meet performance specifications

from 0°C to 70°C. Specifications over the –40°C to 85°C operating

temperature range are assured by design, characterization and correlation

with statistical process controls.

Note 3: Operating junction temperature T

(in °C) is calculated from the

ambient temperature T

and the total continuous package power

dissipation P

(in watts) by the formula:

= T

+ θ

• P

Refer to the Applications Information section for details. This IC includes

overtemperature protection that is intended to protect the device during

momentary overload conditions. Junction temperature will exceed 125°C

when overtemperature protection is active. Continuous operation above

the specified maximum operating junction temperature may result in

device degradation or failure.

Note 4: All current into device pins is positive. All current out of device

pins is negative. All voltages are referenced to GND, unless otherwise

specified.

Note 5: These limits are guaranteed by correlation to wafer level

measurements.

Note 6: Output current may be limited by internal power dissipation. Refer

to the Applications Information section for details.

Note 7: Either TGATE V

may apply for 7.5V < V

< 9V.

Note 8: These limits apply specifically to the thermistor network shown in

Figure 5 in the Applications Information section with the values specified

for a 10k NTC (β of 3750). Limits are then guaranteed by specific V

TEMP

voltage measurements during test.

LTC4011

4011p

TYPICAL PERFOR A CE CHARACTERISTICS

NiCd Charge at 1C 4 Series NiCd 1300mAhr

NiMH Charge at 0.5C

Charger Efficiency at DCIN = 20V,

IOUT = 2A Charge Current Accuracy

Charger Soft-Start Fast Charge Current Line

Regulation

PowerPath Switching

TIME (MINUTES)

CELL VOLTAGE (V)

BATTERY TEMPERATURE (°C)

1.50

1.55

1.60

4011 G01

1.45

1.40

20 40 80

1.35

1.30

1.65

CHARGE CURRENT

BATTERY

TEMPERATURE

SINGLE CELL

VOLTAGE

BATTERY VOLTAGE (V)

EFFICIENCY (%)

100

4011 G04

4 8 12 20142 6 10 18

TEMPERATURE (°C)

–12

CURRENT ERROR (%)

–8

–4

–10

–6

–2

10 20 30 40

4011 G05

500

FAST CHARGE

PRECHARGE

= 12V

BAT = 4.8V

200µs/DIV

VOLTAGE (V)

AMPS (A)

4011 G06

TGATE

BGATE

FAST CHARGE CURRENT

PRECHARGE CURRENT

(V)

–3

CURRENT ERROR (%)

–2

–1

10 14 18 22

4011 G07

26 30

50°C

25°C

0°C

BAT = 4.8V

Fast Charge Current Output

Regulation

BAT (V)

–3

CURRENT ERROR (%)

–2

4011 G08

–1

12 16

50°C

25°C

0°C

VCC = 20V

VOLTAGE (V)

4011 G09

100µs/DIV

DC674A WITH 1kΩ SYSTEM LOAD AND 20kΩ

DCIN SHUNT, CHARGER PAUSED

INFET

DCIN

DCIN OPEN

TIME (MINUTES)

1.30

SINGLE CELL VOLTAGE (V)

BATTERY TEMPEATURE (°C)

1.40

1.50

1.60

1.45

1.55

120

4011 G03

0 20 40 80 100 140 16060 180 200

CHARGE CURRENT

TOP OFF

BATTERY

TEMPERATURE

SINGLE CELL

VOLTAGE

0.5A

4 SERIES NimH 2100mAHr

AA CELLS CHARGED AT 0.5C

TIME (MINUTES)

SINGLE CELL VOLTAGE (V)

BATTERY TEMPERATURE (°C)

1.60

1.65

1.70

4011 G02

1.55

1.50

10 20 40

1.45

1.35

1.40

1.75

CHARGE CURRENT

BATTERY

TEMPERATURE

SINGLE CELL

VOLTAGE

4 SERIES NiCd 1300mAhr

SC CELLS CHARGED AT 2C

LTC4011

4011p

PI FU CTIO S

DCIN (Pin 1): DC Power Sense Input. The LTC4011 senses

voltage on this pin to determine when an external DC

power source is present. This input should be isolated

from V

by a blocking diode or PowerPath FET. Refer to

the Applications Information section for complete details.

Operating voltage range is GND to 34V.

FAULT (Pin 2): Active-Low Fault Indicator Output. The

LTC4011 indicates various battery and internal fault con-

ditions by connecting this pin to GND. Refer to the Opera-

tion and Applications Information sections for further

details. This output is capable of driving an LED and should

be left floating if not used. FAULT is an open-drain output

to GND with an operating voltage range of GND to V

CHRG (Pin 3): Active-Low Charge Indicator Output. The

LTC4011 indicates it is providing charge to the battery by

connecting this pin to GND. Refer to the Operation and

Applications Information sections for further details. This

output is capable of driving an LED and should be left

floating if not used. CHRG is an open-drain output to GND

with an operating voltage range of GND to V

CHEM (Pin 4): Battery Chemistry Selection Input. This pin

should be wired to GND to select NiMH fast charge

termination parameters. If a voltage greater than 2.85V is

applied to this pin, or it is left floating, NiCd parameters are

used. Refer to the Applications Information section for

further details. Operating voltage range is GND to 3.3V.

GND (Pin 5): Ground. This pin provides a single-point

ground for internal references and other critical analog

circuits.

(Pin 6): Thermistor Network Termination Output. The

LTC4011 provides 3.3V on this pin to drive an external

thermistor network connected between V

RT,

TEMP

and

GND. Additional power should not be drawn from this pin

by the host application.

TEMP

(Pin 7): Battery Temperature Input. An external

thermistor network may be connected to V

TEMP

to pro-

vide temperature-based charge qualification and addi-

tional fast charge termination control. Charging may also

be paused by connecting the V

TEMP

pin to GND. Refer to

the Operation and Applications Information sections for

complete details on external thermistor networks and

charge control. If this pin is not used it should be wired

to V

. Operating voltage range is GND to 3.3V.

CELL

(Pin 8): Average Single-Cell Voltage Input. An

external voltage divider between BAT and V

CDIV

is attached

to this pin to monitor the average single-cell voltage of the

battery pack. The LTC4011 uses this information to pro-

tect against catastrophic battery overvoltage and to con-

trol the charging state. Refer to the Applications Information

section for further details on the external divider network.

Operating voltage range is GND to BAT.

CDIV

(Pin 9): Average Cell Voltage Resistor Divider Ter-

mination. The LTC4011 connects this pin to GND provided

the charger is not in shutdown. V

CDIV

is an open-drain

output to GND with an operating voltage range of GND to

BAT.

TIMER (Pin 10): Charge Timer Input. A resistor connected

between TIMER and GND programs charge cycle timing

limits. Refer to the Applications Information section for

complete details. Operating voltage range is GND to 1V.

SENSE (Pin 11): Charge Current Sense Input. An external

resistor between this input and BAT is used to program

charge current. Refer to the Applications Information

section for complete details on programming charge

current. Operating voltage ranges from (BAT – 50mV) to

(BAT + 200mV).

BAT (Pin 12): Battery Pack Connection. The LTC4011 uses

the voltage on this pin to control current sourced from V

to the battery during charging. Allowable operating volt-

age range is GND to V

TOC (Pin 13): Active-Low Top-Off Charge Indicator Out-

put. The LTC4011 indicates the top-off charge state for

NiMH batteries by connecting this pin to GND. Refer to the

Operation and Applications Information sections for fur-

ther details. This output is capable of driving an LED and

should be left floating if not used. TOC is an open-drain

output to GND with an operating voltage range of GND to

LTC4011

4011p

INTV

(Pin 14): Internal 5V Regulator Output. This pin

provides a means of bypassing the internal 5V regulator

used to power the BGATE output driver. Typically, power

should not be drawn from this pin by the application

circuit. Refer to the Application Information section for

additional details.

BGATE (Pin 15): External Synchronous N-channel MOSFET

Gate Control Output. This output provides gate drive to an

optional external NMOS power transistor switch used for

synchronous rectification to increase efficiency in the

step-down DC/DC converter. Operating voltage is GND to

INTV

. BGATE should be left floating if not used.

PGND (Pin 16): Power Ground. This pin provides a return

for switching currents generated by internal LTC4011

circuits. Externally, PGND and GND should be wired

together using a very low impedance connection. Refer to

PCB Layout Considerations in the Applications Informa-

tion section for additional grounding details.

TGATE (Pin 17): External P-channel MOSFET Gate Control

Output. This output provides gate drive to an external

PMOS power transistor switch used in the DC/DC con-

verter. Operating voltage range varies as a function of V

Refer to the Electrical Characteristics table for specific

voltages.

PI FU CTIO S

(Pin 18): Power Input. External PowerPath control

circuits normally connect either the DC input power supply

or the battery to this pin. Refer to the Applications Infor-

mation section for further details. Suggested applied

voltage range is GND to 34V.

READY (Pin 19): Active-Low Ready-to-Charge Output.

The LTC4011 connects this pin to GND if proper operating

voltages for charging are present. Refer to the Operation

section for complete details on charge qualification. This

output is capable of driving an LED and should be left

floating if not used. READY is an open-drain output to GND

with an operating voltage range of GND to V

INFET (Pin 20): PowerPath Control Output. For very low

dropout applications, this output may be used to drive the

gate of an input PMOS pass transistor connected between

the DC input (DCIN) and the raw system supply rail (V

INFET is internally clamped about 6V below V

. Maxi-

mum operating voltage is V

. INFET should be left

floating if not used.

Exposed Pad (Pin 21): This pin provides enhanced

thermal properties for the TSSOP. It must be soldered to

the PCB copper ground to obtain optimum thermal

performance.

LTC4011

4011p

BLOCK DIAGRA

CHARGER

STATE

CONTROL

LOGIC

THERMISTOR

INTERFACE

A/D

CONVERTER

BATTERY

DETECTOR

VOLTAGE

REGULATOR

UVLO AND

SHUTDOWN

PWM

FET DIODE

CHARGE

TIMER

VOLTAGE

REFERENCE

INTERNAL

VOLTAGE

REGULATOR

VTEMP

VRT

4CHEM

3CHRG

2FAULT

DCIN

5GND

VCELL

10 TIMER

9VCDIV

TOC

INTVDD

4011 BD

SENSE

BAT

PGND

READY

INFET

VCC

BGATE

TGATE

LTC4011

4011p

OPERATIO

CHARGE

QUALIFICATION

SHUTDOWN

DC ADAPTER PRESENT

NiCd OR

NiMH – ∆V

CELL

< 1.325V

MAX

IS PROGRAMMED MAXIMUM FAST CHARGE DURATION

**OPTIONAL TEMPERATURE LIMITS APPLY

4011 F01

CELL

< 900mV

CELL

> 900mV

CELL

> 900mV

CELL

< 900mV

CELL

< 1.22V

AT t

MAX

*/12

OR TIME = t

MAX

CELL

> 350mV, ADEQUATE V

CHARGER ENABLED AND

TEMPERATURE OK (OPTIONAL)

CHECK

BATTERY

PRECHARGE**

(C/5 FOR

MAX

/12)

FAST CHARGE**

(1C)

AUTOMATIC

RECHARGE

FAULT

CELL

> 1.95V

OR PWM FAULTS

TOP-OFF

CHARGE**

(C/10)

NiMH

∆T/∆t

NO DC ADAPTER

MAX

NO BATTERY

< 4.25V

Figure 1. LTC4011 State Diagram

LTC4011

4011p

OPERATIO

Shutdown State

The LTC4011 remains in micropower shutdown until

DCIN (Pin 1) is driven above V

(Pin 8). In shutdown all

status and PWM outputs and internally generated termi-

nations or supply voltages are inactive. Current consump-

tion from V

and BAT is reduced to a very low level.

Charge Qualification State

Once DCIN is greater than V

, the LTC4011 exits mi-

cropower shutdown, enables its own internal supplies,

provides V

voltage for temperature sensing, and switches

CDIV

to GND to allow measurement of the average single-

cell voltage. The IC also verifies that V

is at or above

4.25V, V

is 500mV above BAT and V

CELL

is between

350mV and 1.95V. If V

CELL

is above 1.95V, the fault state

is entered, which is described in more detail below. Once

adequate voltage conditions exist for charging, READY is

asserted.

If the voltage between V

TEMP

and GND is below 200mV,

the LTC4011 is paused. If V

TEMP

is above 200mV but

below 2.85V, the LTC4011 verifies that the sensed tem-

perature is between 5°C and 45°C. If these temperature

limits are not met or if its own die temperature is too high,

the LTC4011 will indicate a fault and not allow charging to

begin. If V

TEMP

is greater than 2.85V, battery temperature

related charge qualification, monitoring and termination

are disabled.

Once charging is fully qualified, precharge begins (unless

the LTC4011 is paused). In that case, the V

TEMP

pin is

monitored for further control. The charge status indicators

and PWM outputs remain inactive until charging begins.

Charge Monitoring

The LTC4011 continues to monitor important voltage and

temperature parameters during all charging states. If the

DC input is removed, charging stops and the shutdown

state is entered. If V

drops below 4.25V or V

CELL

drops

below 350mV, charging stops and the LTC4011 returns to

the charge qualification state. If V

CELL

exceeds 1.95V, charg-

ing stops and the IC enters the fault state. If an external

thermistor indicates sensed temperature is beyond a range

of 5°C to 60°C, or the internal die temperature exceeds an

internal thermal limit, charging is suspended, the charge

timer is paused and the LTC4011 indicates a fault condi-

tion. Normal charging resumes from the previous state

when the sensed temperature returns to a satisfactory

range. In addition, other battery faults are detected during

specific charging states as described below.

Precharge State

If the initial voltage on V

CELL

is below 900mV, the LTC4011

enters the precharge state and enables the PWM current

source to trickle charge using one-fifth the programmed

charge current. The CHRG status output is active during

precharge. The precharge state duration is limited to

MAX

/12 minutes, where t

MAX

is the maximum fast charge

period programmed with the TIMER pin. If sufficient V

CELL

voltage cannot be developed in this length of time, the fault

state is entered, otherwise fast charge begins.

Fast Charge State

If adequate average single-cell voltage exists, the LTC4011

enters the fast charge state and begins charging at the

programmed current set by the external current sense

resistor connected between the SENSE and BAT pins. The

CHRG status output is active during fast charge. If V

CELL

is initially above 1.325V, cell voltage processing begins

immediately. Otherwise –∆V termination is disabled for a

stabilization period of t

MAX

/12. In that case, the LTC4011

makes another fault check at t

MAX

/12, requiring the aver-

age cell voltage to be above 1.22V. This ensures the

battery pack is accepting a fast charge. If V

CELL

is not

above this voltage threshold, the fault state is entered. Fast

charge state duration is limited to t

MAX

and the fault state

is entered if this limit is exceeded.

Charge Termination

Fast charge termination parameters are dependent upon

the battery chemistry selected with the CHEM pin. Volt-

age-based termination (–∆V) is always active after the

initial voltage stabilization period. If an external thermistor

network is present, chemistry-specific limits for ∆T/∆t

(rate of temperature rise) are also used in the termination

algorithm. Temperature-based termination, if enabled,

becomes active as soon as the fast charge state is entered.

(Refer to Figure 1)

LTC4011

4011p

Top-Off Charge State

If NiMH fast charge termination occurs because the ∆T/∆t

limit is exceeded after an initial period of t

MAX

/12 has ex-

pired, the LTC4011 enters the top-off charge state. Top-off

charge is implemented by sourcing one-tenth the pro-

grammed charge current for t

MAX

/3 minutes to ensure that

100% charge has been delivered to the battery. The CHRG

and TOC status outputs are active during the top-off state.

If NiCd cells have been selected with the CHEM pin, the

LTC4011 never enters the top-off state.

Automatic Recharge State

Once charging is complete, the automatic recharge state

is entered to address the self-discharge characteristics of

nickel chemistry cells. The charge status outputs are

inactive during automatic recharge, but V

CDIV

remains

switched to GND to monitor the average cell voltage. If the

CELL

voltage drops below 1.325V without falling below

350mV, the charge timer is reset and a new fast charge

cycle is initiated.

The internal termination algorithms of the LTC4011 are

adjusted when a fast charge cycle is initiated from auto-

matic recharge, because the battery should be almost fully

charged. Voltage-based termination is enabled immedi-

ately and the NiMH ∆T/∆t limit is fixed at a battery

temperature rise of 1°C/minute.

Fault State

As discussed previously, the LTC4011 enters the fault

state based on detection of invalid battery voltages during

various charging phases. The IC also monitors the regu-

lation of the PWM control loop and will enter the fault state

if this is not within acceptable limits. Once in the fault state,

the battery must be removed or DC input power must be

cycled in order to initiate further charging. In the fault

state, the FAULT output is active, the READY output is

inactive, charging stops and the charge indicator outputs

are inactive. The V

CDIV

output remains connected to GND

to allow detection of battery removal.

Note that the LTC4011 also uses the FAULT output to

indicate that charging is suspended due to invalid battery

or internal die temperatures. However, the IC does not

enter the fault state in these cases and normal operation

will resume when all temperatures return to acceptable

levels. Refer to the Status Outputs section for more detail.

Insertion and Removal of Batteries

The LTC4011 automatically senses the insertion or re-

moval of a battery by monitoring the V

CELL

pin voltage.

Should this voltage fall below 350mV, the IC considers the

battery to be absent. Removing and then inserting a

battery causes the LTC4011 to initiate a completely new

charge cycle beginning with charge qualification.

External Pause Control

After charging is initiated, the V

TEMP

pin may be used to

pause operation at any time. When the voltage between

TEMP

and GND drops below 200mV, the charge timer

pauses, fast charge termination algorithms are inhibited

and the PWM outputs are disabled. The status and V

CDIV

outputs all remain active. Normal function is fully restored

from the previous state when pause ends.

Status Outputs

The LTC4011 open-drain status outputs provide valuable

information about the IC’s operating state and can be

used for a variety of purposes in applications. Table 1

summarizes the state of the four status outputs and the

VCDIV pin as a function of LTC4011 operation. The status

outputs can directly drive current-limited LEDs termi-

nated to the DC input. The VCDIV column in Table 1is

strictly informational. VCDIV should only be used for the

VCELL resistor divider, as previously discussed.

OPERATIO

Table 1. LTC4011 Status Pins

READY FAULT CHRG TOC V

CDIV

CHARGER STATE

Off Off Off Off Off Off

On Off Off Off On Ready to Charge

TEMP

Held Low)

or Automatic Recharge

On Off On Off On Precharge or Fast Charge

(May be Paused)

On Off On On On NiMH Top-Off Charge

(May be Paused)

On On On or Off On or Off On Temperature Limits

Exceeded

Off On Off Off On Fault State (Latched)

LTC4011

4011p

OPERATIO

–

ITH

IPROG

QPWM CLOCK

BAT

11 SENSE

RSENSE

15 BGATE

17 TGATE

LTC4011

VCC

4011 F02

Figure 2. LTC4011 PWM Control Loop

PWM Current Source Controller

An integral part of the LTC4011 is the PWM current source

controller. The charger uses a synchronous step-down

architecture to produce high efficiency and limited thermal

dissipation. The nominal operating frequency of 550kHz

allows use of a smaller external filter components. The

TGATE and BGATE outputs have internally clamped volt-

age swings. They source peak currents tailored to smaller

surface-mount power FETs likely to appear in applications

providing an average charge current of 3A or less. During

the various charging states, the LTC4011 uses the PWM

controller to regulate an average voltage between SENSE

and BAT that ranges from 10mV to 100mV.

A conceptual diagram of the LTC4011 PWM control loop

is shown in Figure 2.

The voltage across the external current programming

resistor R

SENSE

is averaged by integrating error amplifier

EA. An internal programming current is also pulled from

input resistor R1. The I

PROG

• R1 product establishes the

desired average voltage drop across R

SENSE

, and hence,

the average current through R

SENSE

. The I

output of the

error amplifier is a scaled control current for the input of

the PWM comparator CC. The I

• R3 product sets a peak

current threshold for CC such that the desired average

current through R

SENSE

is maintained. The current com-

parator output does this by switching the state of the SR

latch at the appropriate time.

the beginning of each oscillator cycle, the PWM clock

sets the SR latch and the external P

-channel

MOSFET is

switched on (N

-channel

MOSFET switched off) to refresh

the current carried by the external inductor. The inductor

current and voltage drop across RSENSE begin to rise

linearly. During normal operation, the PFET is turned off

(NFET on) during the cycle by CC when the voltage

difference across RSENSE reaches the peak value set by

the output of EA. The inductor current then ramps down

linearly until the next rising PWM clock edge. This closes

the loop and maintains the desired average charge current

in the external inductor.

Low Dropout Charging

After charging is initiated, the LTC4011 does not require

that V

remain at least 500mV above BAT because

situations exist where low dropout charging might occur.

In one instance, parasitic series resistance may limit PWM

headroom (between V

and BAT) as 100% charge is

reached. A second case can arise when the DC adapter

selected by the end user is not capable of delivering the

current programmed by R

SENSE

, causing the output volt-

age of the adapter to collapse. While in low dropout, the

LTC4011 PWM runs near 100% duty cycle with a fre-

quency that may not be constant and can be less than

550kHz. The charge current will drop below the pro-

grammed value to avoid generating audible noise, so the

actual charge delivered to the battery may depend prima-

rily on the LTC4011 charge timer.

Internal Die Temperature

The LTC4011 provides internal overtemperature detec-

tion to protect against electrical overstress, primarily at

the FET driver outputs. If the die temperature rises above

this thermal limit, the LTC4011 stops switching and

indicates a fault as previously discussed.

LTC4011

4011p

APPLICATIO S I FOR ATIO

WUUU

External DC Source

The external DC power source should be connected to the

charging system and the V

pin through either a power

diode or P-channel MOSFET. This prevents catastrophic

system damage in the event of an input short to ground or

reverse-voltage polarity at the DC input. The LTC4011

automatically senses when this input is present. The open-

circuit voltage of the DC source should be between 4.5V

and 34V, depending on the number of cells being charged.

In order to avoid low dropout operation, ensure 100%

capacity at charge termination, and allow reliable detec-

tion of battery insertion, removal or overvoltage, the

following equation can be used to determine the minimum

full-load voltage that should be provided by the external

DC power source.

DCIN(MIN) = (n • 2V) + 0.3V

where n is the number of series cells in the battery pack.

The LTC4011 will properly charge over a wide range of

DCIN and BAT voltage combinations. Operating the

LTC4011 in low dropout or with DCIN much greater than

BAT will force the PWM frequency to be much less than

550kHz. The LTC4011 disables charging and sets a fault if

a large DCIN to BAT differential would cause generation of

audible noise.

PowerPath Control

Proper PowerPath control is an important consideration

when fast charging nickel cells. This control ensures that

the system load remains powered at all times, but that

normal system operation and associated load transients

do not adversely affect fast charge termination. For high

efficiency and low dropout applications, the LTC4011 can

provide gate drive from the INFET pin directly to an input

P-channel MOSFET.

The battery should also be connected to the raw system

supply by a switch that selects the battery for system power

only if an external DC source is not present. Again, for

applications requiring higher efficiency, a P-channel

MOSFET with its gate driven from the DC input can be used

to perform this switching function (see Figure 8). Gate

voltage clamping may be necessary on an external PMOS

transistor used in this manner at higher input voltages.

Alternatively, a diode can be used in place of this FET.

Battery Chemistry Selection

The desired battery chemistry is selected by programming

the CHEM pin to the proper voltage. If it is wired to GND,

a set of parameters specific to charging NiMH cells is

selected. When CHEM is left floating or connected to V

charging is optimized for NiCd cells. The various charging

parameters are detailed in Table 2.

Programming Charge Current

Charge current is programmed using the following

equation:

RmV

SENSE PROG

=100

SENSE

is an external resistor connected between the

SENSE and BAT pins. A 1% resistor with a low temperature

coefficient and sufficient power dissipation capability to

avoid self-heating effects is recommended.

Programming Maximum Charge Times

Connecting the appropriate resistor between the TIMER

pin and GND programs the maximum duration of various

charging states. To some degree, the value should reflect

how closely the programmed charge current matches the

1C rate of targeted battery packs. The maximum fast

charge period is determined by the following equation:

Rt Hours

TIMER MAX

() ()

•–

Ω=30 10 6

Some typical timing values are detailed in Table 3. R

TIMER

should not be less than 15k. The actual time limits used by

the LTC4011 have a resolution of approximately ±30

seconds in addition to the tolerances given the Electrical

Characteristics table. The maximum time period is ap-

proximately 4.3 hours.

LTC4011

4011p

Cell Voltage Network Design

An external resistor network is required to provide the

average single-cell voltage to the V

CELL

pin of the LTC4011.

The proper circuit for multicell packs is shown in Figure 3.

The ratio of R2 to R1 should be a factor of (n – 1), where

n is the number of series cells in the battery pack. The value

of R1 should be between 1k and 100k. This range limits the

sensing error caused by V

CELL

leakage current and pre-

vents the ON resistance of the internal NFET between V

CDIV

and GND from causing a significant error in the V

CELL

voltage. The external resistor network is also used to

detect battery insertion and removal. The filter formed by

C1 and the parallel combination of R1 and R2 is recom-

mended for rejecting PWM switching noise. The value of

C1 should be chosen to yield a 1st order lowpass fre-

quency of less than 500Hz. In the case of a single cell, the

external application circuit shown in Figure 4 is recom-

mended to provide the necessary noise filtering and miss-

ing battery detection.

APPLICATIO S I FOR ATIO

WUUU

Table 2. LTC4011 Charging Parameters

CHEM BAT

STATE PIN CHEMISTRY TIMER T

MIN

MAX

CHRG

TERMINATION CONDITION

PC Both t

MAX

/12 5°C45°CI

PROG

/5 Timer Expires

FC Open NiCd t

MAX

5°C60°CI

PROG

–20mV per Cell or 2°C/Minute

GND NiMH t

MAX

5°C60°CI

PROG

1.5°C/Minute for First t

MAX

/12 Minutes if Initial

CELL

< 1.325V

–10mV per Cell or 1°C/Minute After t

MAX

/12 Minutes

or if Initial V

CELL

> 1.325V

TOC GND NiMH t

MAX

/3 5°C60°CI

PROG

/10 Timer Expires

AR Both 5°C45°C0V

CELL

< 1.325V

PC: Precharge

FC: Fast Charge (Initial –∆V Termination Hold Off of t

MAX

/12 Minutes May Apply)

TOC: Top-Off Charge (Only for NiMH ∆T/∆t FC Termination After Initial t

MAX

/12 Period)

AR: Automatic Recharge (Temperature Limits Apply to State Termination Only)

Table 3. LTC4011 Time Limit Programming Examples

FAST CHARGE TOP-OFF

TYPICAL FAST PRECHARGE LIMIT VOLTAGE STABILIZATION FAST CHARGE LIMIT CHARGE

TIMER

CHARGE RATE (MINUTES) (MINUTES) (HOURS) (MINUTES)

24.9k 2C 3.8 3.8 0.75 15

33.2k 1.5C 5 5 1 20

49.9k 1C 7.5 7.5 1.5 30

66.5k 0.75C 10 10 2 40

100k C/2 15 15 3 60

BAT

LTC4011 R2 +

FOR TWO OR

MORE SERIES CELLS

R1 C1

R2 = R1(n – 1)

4011 F03

CDIV

GND

CELL

Figure 3. Mulitple Cell Voltage Divider

LTC4011

4011p

APPLICATIO S I FOR ATIO

WUUU

RRT

RR R RR RR R R T

RRT if R k

OOOO

11 164 2

0 141 2

311 46 2 1 2 1 2

12 10

()

=++

()

.–

–

.– ,

βR1

Figure 4. Single-Cell Monitor Network

BAT

10k 10k

33nF

1 CELL

4011 F04

VCDIV

8VCELL

The filter formed by R4 and C1 in Figure 5 is optional but

recommended for rejecting PWM switching noise. Alter-

natively, R4 may be replaced by a short, and a value

chosen for C1 which will provide adequate filtering from

the Thevenin impedance of the remaining thermistor net-

work. The filter pole frequency, which should be less than

500Hz, will vary more with battery temperature without

R4. External components should be chosen to make the

Thevenin impedance from V

TEMP

to GND 100kΩ or less,

including R4, if present.

Figure 5. External NTC Thermistor Network

R2R

51k

10nF

4011 F05

TEMP

Thermistor Network Design

The network for proper temperature sensing using a

thermistor with a negative temperature coefficient (NTC)

is shown in Figure 5. R3 is only required for thermistors

with a room temperature value above 10k. For thermistors

with a room temperature value of 10k or less, replace R3

with a short.

The LTC4011 is designed to work best with a 1% 10k NTC

thermistor with a β of 3750. In this case, the values for the

external network are given by:

R1 = 10.7k

R2 = 30.9k

R3 = 0Ω

However, the LTC4011 will operate with other NTC ther-

mistors having different nominal values or exponential

temperature coefficients. For these thermistors, the gen-

eral-purpose design equations for the passive resistors in

the external linearization network are as follows:

where:

= Thermistor (R

) value at T

(Ω)

= Thermistor reference temperature (°K)

β = Thermistor exponential temperature coefficient of

resistance

Disabling Thermistor Functions

Temperature sensing is optional in LTC4011 applications.

For low cost systems where temperature sensing may not

be required, the V

TEMP

pin may simply be wired to V

disable temperature qualification of all charging opera-

tions. However, this practice is not recommended for

NiMH cells charged well above or below their 1C rate,

because fast charge termination based solely on voltage

inflection may not be adequate to protect the battery from

a severe overcharge. A resistor between 10k and 20k may

be used to connect V

TEMP

to V

if the pause function is

still desired.

LTC4011

4011p

INTV

Regulator Output

If BGATE is left open, the INTV

pin of the LTC4011 can

be used as an additional source of regulated voltage in the

host system any time READY is active. Switching loads on

INTV

may reduce the accuracy of internal analog cir-

cuits used to monitor and terminate fast charging. In

addition, DC current drawn from the INTV

pin can

greatly increase internal power dissipation at elevated V

voltages. A minimum ceramic bypass capacitor of 0.1µF is

recommended.

Calculating Average Power Dissipation

The user should ensure that the maximum rated IC junc-

tion temperature is not exceeded under all operating

conditions. The thermal resistance of the LTC4011 pack-

age (θ

) is 38°C/W, provided the exposed metal pad is

properly soldered to the PCB. The actual thermal resis-

tance in the application will depend on the amount of PCB

copper to which the package is soldered. Feedthrough vias

directly below the package that connect to inner copper

layers are helpful in lowering thermal resistance. The

following formula may be used to estimate the maximum

average power dissipation P

(in watts) of the LTC4011

under normal operating conditions.

P V mA I I k Q Q

IIn

D CC DD VRT TGATE BGATE

VRT DD CC LED

LED

=+++ +

()

⎛

⎝

⎜⎞

⎠

⎟

7 615

3 3 85 60 30

()

––. –

where:

= Average external INTV

load current, if any

VRT

= Load current drawn by the external thermistor

network from V

, if any

TGATE

= Gate charge of external P-channel MOSFET

in coulombs

BGATE

= Gate charge of external N-channel MOSFET

(if used) in coulombs

LED

= Maximum external LED forward voltage

LED

= External LED current-limiting resistor used in

the application

n = Number of LEDs driven by the LTC4011

Sample Applications

Figures 6 through 9 detail sample charger applications of

various complexities. Combined with the Typical Applica-

tion on the first page of this data sheet, these Figures

demonstrate some of the proper configurations of the

LTC4011. MOSFET body diodes are shown in these fig-

ures strictly for reference only.

Figure 6 shows a minimum application, which might be

encountered in low cost NiCd fast charge applications.

FET-based PowerPath control allows for maximum input

voltage range from the DC adapter. The LTC4011 uses

–∆V to terminate the fast charge state, as no external

temperature information is available. Nonsynchronous

PWM switching is employed to reduce external compo-

nent cost. A single LED indicates charging status.

A 3A NiMH application of medium complexity is shown

in Figure 7. PowerPath control that is completely FET-

based allows for both minimum input voltage overhead

and minimum switchover loss when operating from the

battery.

P-channel MOSFET Q4 functions as a switch to connect

the battery to the system load whenever the DC input

adapter is removed. If the maximum battery voltage is less

than the maximum rated V

of Q4, diode D1 and resistor

R5 are not required. Otherwise choose the Zener voltage

of D1 to be less than the maximum rated V

of Q4. R5

provides a bias current of (V

BAT

– V

ZENER

)/(R5 + 20k) for

D1 when the input adapter is removed. Choose R5 to make

this current, which is drawn from the battery, just large

enough to develop the desired V

across D1.

Precharge, fast charge and top-off states are indicated by

external LEDs. The V

TEMP

thermistor network allows the

LTC4011 to accurately terminate fast charge under a

variety of applied charge rates. Use of a synchronous

PWM topology improves efficiency and lowers power

dissipation.

A full-featured 2A LTC4011 application is shown in Fig-

ure 8. FET-based PowerPath allows for maximum input

voltage range from the DC adapter. The inherent voltage

ratings of the V

CELL

, V

CDIV

, SENSE and BAT pins allow

charging of from one to sixteen series nickel cells in this

application, governed only by the V

overhead limits

APPLICATIO S I FOR ATIO

WUUU

LTC4011

4011p

APPLICATIO S I FOR ATIO

WUUU

Figure 7. 3A NiMH Charger with Full PowerPath Control

Figure 6. Minimum LTC4011 Application

INFET

FAULT

CHRG

TOC

READY

TGATE

BGATE

CDIV

CELL

TEMP

LTC4011

GND

TIMER

CHEM

INTV

SENSE

BAT

FROM

ADAPTER

4.5V TO 34V

10µH

10µF

NiCd

PACK

(1AHr)

SYSTEM

LOAD

0.1Ω

10µF

0.1µF

49.9k

33nF

10k

4011 F06

PGND

INFET

FAULT

CHRG

TOC

READY

VCC

TGATE

VCDIV

VCELL

VTEMP

LTC4011

DCIN

TIMER

GND

CHEM

VRT

INTVDD

SENSE

BAT

FROM

ADAPTER

4.5V TO 34V

10µH

6V 20µF

SYSTEM

LOAD

33mΩ

20µFR2

30.9k

10.7k

NiMH PACK

WITH 10k NTC

(3AHr)

4011 F07

10k

20k 49.9k

10k

0.1µF0.033µF 0.068µF

PGND

BGATE

LTC4011

4011p

APPLICATIO S I FOR ATIO

WUUU

previously discussed. The application includes all average

cell voltage and battery temperature sensing circuitry

required for the LTC4011 to utilize its full range of charge

qualification, safety monitoring and fast charge termina-

tion features. A green LED indicates valid DC input voltage

and installed battery, while a pair of red LEDs indicates

charging. A yellow LED indicates fault conditions. The

grounded CHEM pin selects the NiMH charge termination

parameter set.

While the LTC4011 is a complete, standalone solution,

Figure 9 shows that it can also be interfaced to a host

microprocessor. The MCU can control the charger directly

with an open-drain I/O port connected to the V

TEMP

pin, if

that port is low leakage and can tolerate at least 2V. The

charger state is monitored on the four LTC4011 status

outputs. Charging of NiMH batteries is selected in this

example. However, NiCd (CHEM → V

) parameters could

be chosen as well.

Unlike all of the other applications discussed so far, the

battery continues to power the system during charging.

The MCU could be powered directly from the battery or

from any type of post regulator operating from the battery.

In this configuration, the LTC4011 relies expressly on the

ability of the host MCU to know when load transients will

be encountered. The MCU should then pause charging

(and thus –∆V processing) during those events to avoid

premature fast charge termination. If the MPU cannot

reliably perform this function, full PowerPath control

should

be implemented. Excessive battery load current

variations, such as those generated by a post-regulating

PWM, can generate sufficient voltage noise to cause the

LTC4011 to prematurely terminate a charge cycle and/or

prematurely restart a fast charge. In this case, it may be

necessary to inhibit the LTC4011 after charging is com-

plete until external gas gauge circuitry indicates that

recharging is necessary. Shutdown power is applied to the

LTC4011 through the body diode of Q2 in this application.

Figure 8. Full-Featured 2A LTC4011 Application

INFET

FAULT

CHRG

TOC

READY

TGATE

CDIV

CELL

TEMP

LTC4011

DCIN

TIMER

GND

CHEM

INTV

SENSE

BAT

FROM

ADAPTER

4.5V TO 34V

10µH

NiCd PACK

WITH 10k NTC

(2AHr)

SYSTEM

LOAD

0.05Ω

10µF

33nF 30.9k 10.7k

22nF

0.1µF

10k

51k

10µF

4011 F08

RG Y

20k 49.9k

3k 3k 3k

10k

PGND

BGATE

LTC4011

4011p

Waveforms

Sample waveforms for a standalone application during a

typical charge cycle are shown in Figure 10. Note that

these waveforms are not to scale and do not represent the

complete range of possible activity. The figure is simply

intended to allow better conceptual understanding and to

highlight the relative behavior of certain signals generated

by the LTC4011 during a typical charge cycle.

Initially, the LTC4011 is in low power shutdown as the

system operates from a heavily discharged battery. A DC

adapter is then connected such that V

rises above 4.25V

and is 500mV above BAT. The READY output is asserted

when the LTC4011 completes charge qualification.

When the LTC4011 determines charging should begin, it

starts a precharge cycle because V

CELL

is less than 900mV.

As long as the temperature remains within prescribed

limits, the LTC4011 charges (TGATE switching), applying

limited current to the battery with the PWM in order to

bring the average cell voltage to 900mV.

APPLICATIO S I FOR ATIO

WUUU

When the precharge state timer expires, the LTC4011 be-

gins fast charge if V

CELL

is greater than 900mV. The PWM,

charge timer and internal termination control are sus-

pended if pause is asserted (V

CELL

< 200mV), but all status

outputs continue to indicate charging is in progress. The

fast charge state continues until the selected voltage or

temperature termination criteria are met. Figure 10 sug-

gests termination based on ∆T/∆t, which for NiMH would

be an increase of 1°C per minute.

Because NiMH charging terminated due to ∆T/∆t and the

fast charge cycle had lasted more than t

MAX

/12 minutes,

the LTC4011 begins a top-off charge with a current of

PROG

/10. Top-off is an internally timed charge of t

MAX

minutes with the CHRG and TOC outputs continuously

asserted.

Finally, the LTC4011 enters the automatic recharge state

where the CHRG and TOC outputs are deasserted. The

PWM is disabled but V

CDIV

remains asserted to monitor

CELL

. The charge timer will be reset and fast charging will

resume if V

CELL

drops below 1.325V. The LTC4011 enters

Figure 9. LTC4011 with MCU Interface

INFET

FAULT

CHRG

TOC

READY

TGATE

CDIV

CELL

LTC4011

DCIN

INTV

SENSE

BAT

FROM

ADAPTER

4.5V TO 34V

STATUS

MCU

PAUSE

FROM

MCU

10µH

10µF

NiCd PACK

WITH 10k NTC

(1AHr)

SYSTEM

LOAD

0.1Ω

4011 F09

TEMP

GND

CHEM

20k

49.9k 10k

33nF

68nF 30.9k

10.7k

0.1µF

BGATE

PGND

TIMER

LTC4011

4011p

APPLICATIO S I FOR ATIO

WUUU

shutdown when the DC adapter is removed, minimizing

current draw from the battery in the absence of an input

power source.

While not a part of the sample waveforms of Figure 10,

temperature qualification is an ongoing part of the charg-

ing process, if an external thermistor network is detected

by the LTC4011. Should prescribed temperature limits be

exceeded during any particular charging state, charging

would be suspended until the sensed temperature re-

turned to an acceptable range.

Battery-Controlled Charging

Because of the programming arrangement of the LTC4011,

it may be possible to configure it for battery-controlled

charging. In this case, the battery pack is designed to pro-

vide customized information to an LTC4011-based charger,

allowing a single design to service a wide range of appli-

cation batteries. Assume the charger is designed to pro-

vide a maximum charge current of 800mA (R

SENSE

125mΩ). Figure 11 shows a 5V NiCd battery pack for which

800mA represents a 0.75C rate. When connected to the

charger, this pack would provide battery temperature in-

formation and correctly configure both fast charge termi-

nation parameters and time limits for the internal NiCd cells.

A second possibility is to configure an LTC4011-based

charger to accept battery packs with varying numbers of

cells. By including R2 of the average cell voltage divider

network shown in Figure 3, battery-based programming

of the number of series-stacked cells could be realized

without defeating LTC4011 detection of battery insertion

or removal. Figure 12 shows a 2-cell NiMH battery pack

Figure 11. NiCd Battery Pack with Time Limit Control

Figure 10. Charging Waveforms Example

SHDN

VCC = 4.25VDCIN

READY

VCDIV

TGATE

VCELL

CHRG

TOC

VTEMP

(PAUSE)

SHDNTOP-OFF AUTO

RECHARGE

FAST CHARGEPRECHARGE

0.9V

EXTERNAL

PAUSE

200mV

4011 F10

1200mAhr

NiCd CELLS

BATTERY

PACK

TEMP

CHEM

TIMER

66.5k

4011 F11

–

10k

NTC

LTC4011

4011p

APPLICATIO S I FOR ATIO

WUUU

that programs the correct number of series cells when it

is connected to the charger, along with indicating chem-

istry and providing temperature information.

Any of these battery pack charge control concepts could

be combined in a variety of ways to service custom

application needs.

1. Input capacitors should be placed as close as possible

to switching FET supply and ground connections with

the shortest copper traces possible. The switching

FETs must be on the same layer of copper as the input

capacitors. Vias should not be used to make these

connections.

2. Place the LTC4011 close to the switching FET gate

terminals, keeping the connecting traces short to

produce clean drive signals. This rule also applies to

IC supply and ground pins that connect to the switch-

ing FET source pins. The IC can be placed on the

opposite side of the PCB from the switching FETs.

3. Place the inductor input as close as possible to the

drain of the switching FETs. Minimize the surface area

of the switch node. Make the trace width the minimum

needed to support the programmed charge current.

Use no copper fills or pours. Avoid running the con-

nection on multiple copper layers in parallel. Minimize

capacitance from the switch node to any other trace or

plane.

4. Place the charge current sense resistor immediately

adjacent to the inductor output, and orient it such that

current sense traces to the LTC4011 are short. These

feedback traces need to be run together as a single pair

with the smallest spacing possible on any given layer

on which they are routed. Locate any filter component

on these traces next to the LTC4011, and not at the

sense resistor location.

5. Place output capacitors adjacent to the sense resisitor

output and ground.

6. Output capacitor ground connections must feed into

the same copper that connects to the input capacitor

ground before tying back into system ground.

Figure 12. NiMH Battery Pack Indicating Number of Cells

Figure 13. High Speed Switching Path

PCB Layout Considerations

To prevent magnetic and electrical field radiation and high

frequency resonant problems, proper layout of the com-

ponents connected to the LTC4011 is essential. Refer to

Figure 13. For maximum efficiency, the switch node rise

and fall times should be minimized. The following PCB

design priority list will help ensure proper topology. Lay-

out the PCB using this specific order.

1500mAhr

NiMH CELLS

BATTERY

PACK

TEMP

CELL

CHEM

4011 F12

–

10k

NTC

4011 F13

BAT

HIGH

FREQUENCY

CIRCULATING

PATH

BAT

SWITCH NODE

SWITCHING GROUND

OUT

LTC4011

4011p

APPLICATIO S I FOR ATIO

WUUU

7. Connection of switching ground to system ground, or

any internal ground plane should be single-point. If

the system has an internal system ground plane, a

good way to do this is to cluster vias into a single star

point to make the connection.

8. Route analog ground as a trace tied back to the

LTC4011 GND pin before connecting to any other

ground. Avoid using the system ground plane. A

useful CAD technique is to make analog ground a

separate ground net and use a 0Ω resistor to connect

analog ground to system ground.

9. A good rule of thumb for via count in a given high

current path is to use 0.5A per via. Be consistent when

applying this rule.

Figure 14. Kelvin Sensing of Charge Current

10. If possible, place all the parts listed above on the same

PCB layer.

11. Copper fills or pours are good for all power connec-

tions except as noted above in Rule 3. Copper planes

on multiple layers can also be used in parallel. This

helps with thermal management and lowers trace

inductance, which further improves EMI performance.

12. For best current programming accuracy, provide a

Kelvin connection from R

SENSE

to SENSE and BAT.

See Figure 14 for an example.

13. It is important to minimize parasitic capacitance on

the TIMER, SENSE and BAT pins. The traces connect-

ing these pins to their respective resistors should be

as short as possible.

SENSE

4011 F14

DIRECTION OF CHARGING CURRENT

SENSE

BAT

LTC4011

4011p

PACKAGE DESCRIPTIO

FE Package

20-Lead Plastic TSSOP (4.4mm)

(Reference LTC DWG # 05-08-1663)

Exposed Pad Variation CB

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 represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

FE20 (CB) TSSOP 0204

0.09 – 0.20

(.0035 – .0079)

0° – 8°

0.25

REF

RECOMMENDED SOLDER PAD LAYOUT

0.50 – 0.75

(.020 – .030)

4.30 – 4.50*

(.169 – .177)

134

5678910

111214 13

6.40 – 6.60*

(.252 – .260)

3.86

(.152)

2.74

(.108)

20 1918 17 16 15

1.20

(.047)

MAX

0.05 – 0.15

(.002 – .006)

0.65

(.0256)

BSC 0.195 – 0.30

(.0077 – .0118)

TYP

2.74

(.108)

0.45 ±0.05

0.65 BSC

4.50 ±0.10

6.60 ±0.10

1.05 ±0.10

3.86

(.152)

MILLIMETERS

(INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.150mm (.006") PER SIDE

NOTE:

1. CONTROLLING DIMENSION: MILLIMETERS

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE

SEE NOTE 4

4. RECOMMENDED MINIMUM PCB METAL SIZE

FOR EXPOSED PAD ATTACHMENT

6.40

(.252)

BSC

LTC4011

4011p

LT/TP 0205 1K • PRINTED IN THE USA

PART NUMBER DESCRIPTION COMMENTS

LTC1325 Microprocessor-Controlled Battery Management System Can Charge, Discharge and Gas Gauge Nickel and Lead-Acid

Batteries with Software Charging Profiles

LT®1510 Constant-Voltage/Constant-Current Battery Charger Up to 1.5A Charge Current for Li-Ion, NiCd and NiMH Batteries

LT1511 3A Constant-Voltage/Constant-Current Battery Charger High Efficiency, Minimum External Components to Fast Charge

Lithium, NiMH and NiCd Batteries

LT1513 SEPIC Constant- or Programmable-Current/Constant- Charger Input Voltage May be Higher, Equal to or Lower Than

Voltage Battery Charger Battery Voltage, 500kHz Switching Frequency

LTC1760 Smart Battery System Manager Autonomous Power Management and Battery Charging for Two

Smart Batteries, SMBus Rev 1.1 Compliant

LTC1960 Dual Battery Charger/Selector with SPI 11-Bit V-DAC, 0.8% Voltage Accuracy, 10-Bit I-DAC,

5% Current Accuracy

LTC4008 High Efficiency, Programmable Voltage/Current Battery Constant-Current/Constant-Voltage Switching Regulator, Resistor

Charger Voltage/Current Programming, AC Adapter Current Limit and

Thermistor Sensor and Indicator Outputs

LTC4010 High Efficiency Standalone Nickel Battery Charger Complete NiMH/NiCd Charger in a Small 16-Pin Package,

Constant-Current Switching Regulator

LTC4060 Standalone Linear NiMH/NiCd Fast Charger Complete NiMH/NiCd Charger in a Small Leaded or Leadless

16-Pin Package, No Sense Resistor or Blocking Diode Required

LTC4100 Smart Battery Charger Controller Level 2 Charger Operates with or without MCU Host,

SMBus Rev. 1.1 Compliant

LTC4150 Coulomb Counter/Battery Gas Gauge High Side Sense of Charge Quantity and Polarity in a 10-Pin MSOP

LTC4412 Low Loss PowerPath Controller Very Low Loss Replacement for Power Supply ORing Diodes

Using Minimal External Components

RELATED PARTS

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900

●

FAX: (408) 434-0507

●