ANALOG DEVICES LTC 4011 CFE Datasheet

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Page 1

High Efﬁciency Standalone

0.1µF

10µF

4.7µH

10µF

0.033µF 0.068µF

FAULT

INFET

CHRG

FROM

ADAPTER

TOC READY

Nickel Battery Charger

FeaTures DescripTion

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

applicaTions

Integrated or Standalone Battery Charger

Portable Instruments or Consumer Products

Battery-Powered Diagnostics and Control

Back-Up Battery Management

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.

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 discharged batteries are precharged with a trickle cur rent. 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 automatically applied to NiMH batteries after fast charg

completed. The IC will also resume charging if the

ing is 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 temperature limits. NiMH or NiCd fast charge termination parameters 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.

LTC4011

Typical applicaTion

2A NiMH Battery Charger

2A NiMH Charge Cycle at 1C

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LTC4011

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

(Note 1)

VCC (Input Supply) to GND......................... –0.3V to 36V

DCIN to GND ..............................................–0.3V to 36V

, V

FAULT, CHRG, V

CELL

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

, SENSE, BAT, TOC

CDIV

+ 0.3V

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

CHEM, V

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

TEMP

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

Operating Ambient Temperature Range

(Note 2) ........................................................ 0°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

orDer inForMaTion

pin conFiguraTionabsoluTe MaxiMuM raTings

= 125°C, θJA = 38°C/W

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

JMAX

OBTAIN SPECIFIED THERMAL RESISTANCE

LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC4011CFE#PBF LTC4011CFE#TRPBF LTC4011CFE 20-Lead

Plastic TSSOP 0°C to 85°C

LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC4011CFE LTC4011CFE#TR LTC4011CFE 20-Lead

Plastic TSSOP 0°C to 85°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/

more information on tape and reel speciﬁcations, go to: http://www.linear.com/tapeandreel/

For

elecTrical characTerisTics

(Note 4) 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.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Supply

SHDN

UVLO

UV(HYST)

SHDNI

SHDND

INTV

Output Voltage No Load

INTV

DD(MIN)

Input Voltage Range

Shutdown Quiescent Current (Note 5) VCC = BAT = 4.8V

Quiescent Current Waiting to Charge (Pause)

Operating Current Fast Charge State, No Gate Load

Undervoltage Threshold Voltage VCC Increasing

Undervoltage Hysteresis Voltage

Shutdown Threshold Voltage DCIN – VCC, DCIN Increasing

Shutdown Threshold Voltage DCIN – VCC, DCIN Decreasing

Charge Enable Threshold Voltage VCC – BAT, VCC Increasing

Regulator

Short-Circuit Current (Note 6) INTVDD = 0V

Output Voltage VCC = 4.5V, IDD = –10mA

4.5 34

5 10

3.85 4.2 4.45 V

3 5 mA

5 9 mA

170 mV

5 30 60 mV

–60 –25 –5 mV

400 510 600 mV

4.5 5 5.5 V

–100 –50 –10 mA

3.85 V

µA

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LTC4011

elecTrical characTerisTics

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.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Thermistor Termination

Output Voltage RL = 10k

Short-Circuit Current VRT = 0V

PWM Current Source

BAT – SENSE Full-Scale Regulation Voltage (Fast Charge)

BAT – SENSE Precharge Regulation Voltage 0.3V < BAT < VCC – 0.3V (Note 5)

BAT – SENSE Top-Off Charge Regulation Voltage

∆V

BAT

SENSE

OFF

TYP

MIN

OL(TG)

OH(TG)

R(TG)

F(TG)

OL(BG)

OH(BG)

R(BG)

F(BG)

MAX

BAT – SENSE Line Regulation 5.5V < VCC < 25V, Fast Charge

BAT Input Bias Current 0.3V < BAT < VCC – 0.1V

SENSE Input Bias Current SENSE = BAT

Input Bias Current SENSE or BAT, V

Typical Switching Frequency

Minimum Switching Frequency

Maximum Duty Cycle

TGATE Output Voltage Low (V

– TGATE, Note 7)

TGATE Output Voltage High VCC – TGATE, No Load

TGATE Rise Time C

TGATE Fall Time C

BGATE Output Voltage Low No Load

BGATE Output Voltage High No Load

BGATE Rise Time C

BGATE Fall Time C

ADC Inputs

LEAK

Analog Channel Leakage 0V < V

Charger Thresholds

∆V

∆T

BOV

MFC

FCBF

TERM

MIN

MAXI

Battery Present Threshold Voltage

Battery Overvoltage

Minimum Fast Charge Voltage

Fast Charge Battery Fault Voltage

–∆V Termination CHEM OPEN (NiCd)

Automatic Recharge Voltage V

∆T Termination (Note 8)

Minimum Charging Temperature (Note 8) V

Maximum Charge Initiation Temperature (Note 8)

0.3V < BAT < VCC – 0.3V (Note 5) BAT = 4.8V

BAT = 4.8V

0.3V < BAT < VCC – 0.3V (Note 5) BAT = 4.8V

= 0V

CELL

> 9V, No Load

< 7V, No Load

= 3nF, 10% to 90%

LOAD

= 3nF, 10% to 90%

LOAD

= 1.6nF, 10% to 90%

LOAD

= 1.6nF, 10% to 90%

LOAD

< 2V, 550mV < V

CELL

TEMP

CHEM = 0V (NiMH)

Decreasing

CELL

CHEM = 3.3V (NiCd) CHEM = 0V (NiMH)

Increasing

TEMP

Decreasing, Not Charging

TEMP

< 2V

3.075

●

–9 –1 mA

95 95

16 16

6.5

–2 2 mA

–1 0 1 µA

●

460 550 640 kHz

●

20 30 kHz

●

98 99 %

●●

●

●●

●

●●

●

– 0.5

INTVDD – 0.075 INTV

320 350 370 mV

1.815 1.95 2.085 V

850 900 950 mV

1.17 1.22 1.27 V

1.260 1.325 1.390 V

1.3

0.5

0 5 9 °C

41.5 45 47 °C

3.3 3.525

3.6

100 100

20 20

10 10

105 105

24 24

13.5

mV mV

±0.3 mV

50 150 µA

5.6

8.75 V

0 50 mV

35 100 ns

45 100 ns

0 50 mV

35 80 ns

15 80 ns

±100 nA

20 10

2 1

25 14

2.7

1.5

mV mV

°C/min °C/min

V V

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LTC4011

elecTrical characTerisTics

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.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

57 60 63 °C

MAXC

Maximum Fast Charge Temperature

Decreasing, Fast Charge

TEMP

(Note 8)

TEMP(D)

TEMP(P)

Disable Threshold Voltage

TEMP

Pause Threshold Voltage

Charger Timing

∆t

TIMER

MAX

Internal Time Base Error

Programmable Timer Error R

TIMER

= 49.9k

PowerPath Control

OL(INFET)

OH(INFET)

OFF(INFET)

INFET Forward Regulation Voltage DCIN – V

Output Voltage Low VCC – INFET, No Load

Output Voltage High VCC – INFET, No Load

INFET OFF Delay Time C

= 10nF, INFET to 50%

LOAD

Status and Chemistry Select

Output Voltage Low (I

= 10mA) V

LOAD

CDIV

All Other Status Outputs

LKG

IH(VCDIV)

Output Leakage Current All Status Outputs Inactive, V

Input Current High V

CDIV

= V

BAT

Input Voltage Low CHEM (NiMH)

Input Voltage High CHEM (NiCd)

Input Current Low CHEM = GND

Input Current High CHEM = 3.3V

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 LTC4011C is guaranteed to meet performance speciﬁcations from 0°C to 70°C. Speciﬁcations over the 0°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls.

Note 3: Operating junction temperature T the ambient temperature T dissipation P

(in watts) by the formula:

= TA + θ

• PD

and the total continuous package power

(in °C) is calculated from

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

= V

OUT

(Shutdown)

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 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 (

voltage measurements during test.

●

2.8 3.3 V

●

130 280 mV

●

–10 10 %

●

–20 20 %

●

15 55 100 mV

●

3.75 5.2 7 V

●

0 50 mV

3 15 µs

●●

●

–10 10 µA

●

–1 1 µA

●

2.85 V

●

–20 –5 µA

●

–20 20 µA

●

may apply for 7.5V < VCC < 9V.

3750). Limits are then guaranteed by speciﬁc V

β of

435 300

700 600

mV mV

900 mV

TEMP

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Typical perForMance characTerisTics

LTC4011

NiCd Charge Cycle at 1C

NiMH Charge Cycle at 0.5C

NiCd Charge Cycle at 2C

Battery Present Threshold Voltage (per Cell)

Minimum Fast Charge Threshold Voltage (per Cell)

Automatic Recharge Threshold Voltage (per Cell)

Battery Overvoltage Threshold Voltage (per Cell) –∆V Termination Voltage (per Cell)

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LTC4011

Typical perForMance characTerisTics

Programmable Timer Accuracy Charge Current Accuracy

Charger Efﬁciency at I

OUT

= 2A

Charger Soft-Start

PWM Switching Frequency

Fast Charge Current Line Regulation

Fast Charge Current Output Regulation

INFET Forward Regulation Voltage

INFET OFF Delay Time

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Typical perForMance characTerisTics

100µs/DIV

CURRENT (µA)

LTC4011

PowerPath Switching

Undervoltage Lockout Threshold Voltage

Shutdown Quiescent Current PWM Input Bias Current (OFF)

Shutdown Threshold Voltage (DCIN – VCC)

Charge Enable Threshold Voltage (VCC – BAT)

Thermistor Disable Threshold Voltage

Pause Threshold Voltage

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LTC4011

Typical perForMance characTerisTics

INTV

Voltage

INTVDD Short-Circuit Current

pin FuncTions

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 conditions 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.

FAULT is an

GND with an operating voltage range of GND to V

CHRG (Pin 3):

Active-Low Charge Indicator Output. The

open-drain output to

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

with an operating voltage range of GND to V

open-drain output to GND

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, VTEMP

and GND. Additional power should not be drawn from this pin by the host application.

(Pin 7): Battery Temperature Input. An external

TEMP

thermistor network may be connected to V

TEMP

to provide temperature-based charge qualiﬁcation and additional fast charge termination control. Charging may also be paused by connecting the V

pin to GND. Refer to

TEMP

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

. Operating voltage range is GND to 3.3V.

to V

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

CELL

nal voltage divider between BAT and V

is attached to

CDIV

this pin to monitor the average single-cell voltage of the battery pack. The LTC4011 uses this information to protect against catastrophic battery overvoltage and to control the charging state. Refer to the Applications Information section for further details on the external divider network. Operating voltage range is GND to BAT.

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pin FuncTions

LTC4011

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

CDIV

nation. The LTC4011 connects this pin to GND provided the charger is not in shutdown. V

is an open-drain output

CDIV

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

voltage 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 further details. This output is capable of driving an LED

TOC

and should be left ﬂoating if not used.

is an opendrain output to GND with an operating voltage range of GND to V

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 Information 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 converter. Op erating voltage

range varies as a function of V

. Refer to

the Electrical Characteristics table for speciﬁc voltages.

(Pin 18): Power Input. External PowerPath control

circuits normally connect either the DC input power sup-

the battery to this pin. Refer to the Applications

ply or Information 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

GND with an operating voltage range of GND to V

open-drain output to

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 Maximum operating voltage is V

). INFET is internally clamped about 6V below VCC.

. 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.

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LTC4011

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

TEMP

CHEM

CHRG

FAULT

DCIN

GND

CELL

TIMER

CDIV

TOC

INTV

4011 BD

SENSE

BAT

PGND

READY

INFET

BGATE

TGATE

block DiagraM

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Page 11

operaTion

LTC4011

Figure 1. LTC4011 State Diagram

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Page 12

LTC4011

operaTion

(Refer to Figure 1)

Shutdown State

The LTC4011 remains in micropower shutdown until DCIN (Pin 1) is driven above V

(Pin 18). In shutdown all status

and PWM outputs and internally generated terminations or supply voltages are inactive. Current consumption from VCC and BAT is reduced to a very low level.

Charge Qualiﬁcation State

Once DCIN is greater than V

, the LTC4011 exits

micropower shutdown, enables its own internal supplies, provides V V

CDIV

cell voltage. The IC also veriﬁes that V

is 510mV above BAT and V

1.95V. If V if V

CELL

voltage for temperature sensing, and switches

to GND to allow measurement of the average single-

is at or above 4.2V,

is between 350mV and

CELL

is below 350mV, no charging will occur, and

CELL

is above 1.95V, the fault state is entered, which is described in more detail below. Once adequate voltage conditions exist for charging,

If the voltage between V LTC4011 is paused. If V

and GND is below 200mV, the

TEMP

READY is

is above 200mV but below

asserted.

2.85V, the LTC4011 veriﬁes that the sensed temperature 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.

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

is below 900mV, the LTC4011

CELL

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

/12 minutes, where t

MAX

is the maximum fast charge

MAX

period programmed with the TIMER pin. If sufﬁcient V 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.

CHRG status output

The

is initially above 1.325V, voltage-based termination

CELL

is active during fast charge. If

processing begins immediately. Otherwise –∆V termination is disabled for a stabilization period of t

/12. In that

MAX

case, the LTC4011 makes another fault check at t

requiring the average cell voltage to be above 1.22V. This

ensures the battery pack is accepting a fast charge. If

is not above this voltage threshold, the fault state is

CELL

entered. Fast charge state duration is limited to t

the fault state is entered if this limit is exceeded.

MAX

CELL

/12,

and

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

exceeds 1.95V,

CELL

charging 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 condition.

Charge Termination

Fast charge termination parameters are dependent upon the battery chemistry selected with the CHEM pin. Voltagebased 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 tem

rature rise) are also used in the termination algorithm.

pe Temperature-based termination, if enabled, becomes active as soon as the fast charge state is entered. Successful charge termination requires a charge rate between C/2 and 2C. Lower rates may not produce the battery voltage and temperature proﬁle required for charge termination.

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Page 13

operaTion

LTC4011

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 expired, the LTC4011 enters the top-off charge state. Top-off charge is implemented by sourcing one-tenth the programmed charge current for t

/3 minutes to ensure

MAX

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 V

voltage drops below 1.325V without falling below

CELL

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 immediately 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 vari ous charging

phases. The IC also monitors the regulation 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

output remains connected to GND

CDIV

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 removal of a battery by monitoring the V

pin voltage. Should

CELL

this voltage fall below 350mV, the IC considers the bat-

to be absent. Removing and then inserting a battery

tery causes the LTC4011 to initiate a completely new charge cycle beginning with charge qualiﬁcation.

External Pause Control

After charging is initiated, the V

pin may be used to

TEMP

pause operation at any time. When the voltage between

and GND drops below 200mV, the charge timer

TEMP

pauses, fast charge termination algorithms are inhibited and the PWM outputs are disabled. The status and V 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

pin as a function of LTC4011 operation. The status

CDIV

outputs can directly drive current-limited LEDs terminated to the DC input. The V informational. V

should only be used for the V

CDIV

column in Table 1is strictly

CDIV

resistor divider, as previously discussed.

Table 1. LTC4011 Status Pins

READY FAULT CHRG TOC V

Off Off Off Off Off Off

On Off Off Off On Ready

On Off On Off On Precharge

On Off On On On NiMH

On On On o

Off On Off Off On Fault

r Off On or Off On Temperature Limits

CDIV

CHARGER STATE

to Charge

Held Low)

TEMP

or Automatic Recharge

or Fast Charge

(May be Paused)

Top-Off Charge

(May be Paused)

Exceeded

State (Latched)

CDIV

CELL

4011fb

Page 14

LTC4011

–

PROG

PWM CLOCK

S R

BAT

SENSE

BGATE

TGATE

LTC4011

4011 F02

operaTion

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

is averaged by integrating error ampliﬁer

SENSE

EA. An internal programming current is also pulled from input resistor R1. The I desired average voltage drop across R the average current through R

• R1 product establishes the

PROG

SENSE

. The ITH output of

SENSE

the error ampliﬁer is a scaled control current for the input

Figure 2. LTC4011 PWM Control Loop

, and hence,

of the PWM comparator CC. The I

• R3 product sets a

peak current threshold for CC such that the desired aver-

age current

through R

is maintained. The current

SENSE

comparator 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 switched on (N

-channel

MOSFET switched off) to refresh

-channel

MOSFET is

the current carried by the external inductor. The inductor

current and voltage drop across R

begin to rise

SENSE

linearly. During normal operation, the PFET is turned off (NFET on) during the cycle by CC when the voltage difference across R

reaches the peak value set by

SENSE

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 situ-

ations 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

, causing the output volt-

SENSE

age of the adapter to collapse. While in low dropout, the LTC4011 PWM runs near 100% duty cycle with a frequency

that may not be constant and can be less than 550kHz.

The charge current will drop below the programmed value

to avoid generating audible noise, so the actual charge

delivered to the battery may depend primarily on the LTC4011 charge timer.

Internal Die Temperature

The LTC4011 provides internal overtemperature detection

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.

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Page 15

applicaTions inForMaTion

SENSE

PROG

100

LTC4011

External DC Source

The external DC power source should be connected to the charging system and the V 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 auto matically 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 detection 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.

pin through either a power

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:

R SENSE and BAT pins. A 1% resistor with a low temperature coefﬁcient and sufﬁcient power dissipation capability to avoid self-heating effects is recommended. Charge rate

should be between approximately C/2 and 2C.

Inductor Value Selection

For many applications, 10µH represents an optimum value

for the inductor the PWM uses to generate charge current. For applications with I

from an external DC source of 15V or less, values between

5µH and 7.5µH can often be selected. For wider operating

conditions the following equation can be used as a guide for selecting the minimum inductor value.

L > 6.5 • 10

Actual part selection should account for both manufacturing

tolerance and temperature coefﬁcient to ensure this mini

mum. A

the calculated minimum by 1.4 and rounding up or down

to the nearest standard inductance value.

Ultimately, there is no substitute for bench evaluation of

the selected inductor in the target application, which can

also be affected by other environmental factors such as

ambient operating temperature. Using inductor values

lower than recommended by the equation shown above

can result in a fault condition at the start of precharge or

top-off charge.

is an external resistor connected between the

SENSE

of 1.5A or greater running

PROG

–6

• V

good initial selection can be made by multiplying

DCIN

• R

SENSE

, L ≥ 4.7µH

4011fb

Page 16

LTC4011

BAT

LTC4011 R2

FOR TWO OR

MORE SERIES CELLS

R1 C1

R2 = R1(n – 1)

4011 F03

CDIV

GND

CELL

applicaTions inForMaTion

Table 2. LTC4011 Charging Parameters

STATE

PC Both t

FC Open NiCd t

TOC GND NiMH t

AR Both 5°C 45°C 0 V

PC: Precharge FC: Fast TOC: Top-Off Charge (Only for NiMH ∆T/∆t FC Termination After Initial t AR: Automatic Recharge (Temperature Limits Apply to State Termination Only)

CHEM

GND NiMH t

Charge (Initial –∆V Termination Hold Off of t

Table 3. LTC4011 Time Limit Programming Examples

TYPICAL FAST

TIMER

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

CHARGE RATE

BAT

CHEMISTRY TIMER T

/12 5°C 45°C I

MAX

/3 5°C 60°C I

MAX

PRECHARGE LIMIT

(MINUTES)

MIN

5°C 60°C I

/12 Minutes May Apply)

MAX

VOLT

MAXICHRG

/5 Timer Expires

PROG

/10 Timer Expires

PROG

/12 Period)

MAX

FAST

CHARGE

AGE STABILIZATION

(MINUTES)

TERMINATION CONDITION

–20mV per Cell or 2°C/Minute

1.5°C/Minute for First t V

< 1.325V

CELL

–10mV per Cell or 1°C/Minute After t or if Initial V

< 1.325V

CELL

> 1.325V

CELL

FAST

CHARGE LIMIT

(HOURS)

/12 Minutes if Initial

MAX

/12 Minutes

MAX

TOP-OFF

CHARGE

(MINUTES)

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:

Some typical timing values are detailed in Table 3. R 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. If the timer ends without a valid –∆V or ∆T/∆t charge termination, the charger enters the fault state. The maximum time period is approximately 4.3 hours.

Cell Voltage Network Design

An external resistor network is required to provide the average single-cell voltage to the V

pin of the LTC4011.

CELL

TIMER

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

leakage current

CELL

and prevents the ON resistance of the internal NFET between V the V

and GND from causing a signiﬁcant error in

CDIV

voltage. The external resistor network is also

CELL

used to detect battery insertion and removal. The ﬁlter

formed by C1 and the parallel combination of R1 and R2

Figure 3. Mulitple Cell Voltage Divider

4011fb

Page 17

applicaTions inForMaTion

BAT

10k

33nF

1 CELL

4011 F04

CDIV

CELL

R2R

51k

C1 10nF

4011 F05

TEMP

is recommended for rejecting PWM switching noise. The value of C1 should be chosen to yield a 1st order lowpass frequency of less than 500Hz. In the case of a single cell, the external application circuit shown in Figure 4 is rec ommended to missing battery detection.

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 present for thermistors with an exponential temperature coefﬁcient (

3750. For thermistors with β below 3750, with a short.

provide the necessary noise ﬁltering and

β) above

replace R3

where:

= thermistor resistance (Ω) at T

LTC4011

T0 = thermistor reference temperature (°K)

exponential temperature coefﬁcient of resistance

β =

Figure 4. Single-Cell Monitor Network

For thermistors with β less than

3750, the equation for R3 yields a negative number. This number should be used to compute R2, even though R3 is replaced with a short in the actual application. An additional high temperature charge qualiﬁcation error of between 0°C and 5°C may occur when using thermistors with with nominal β less

than 3300 should be avoided.

β lower than

3750. Thermistors

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

Figure 5. External NTC Thermistor Network

but recommended for rejecting PWM switching noise. Alternatively, R4 may be replaced by a short, and a value

The LTC4011 is designed to work best with a 5% 10K NTC thermistor with a β near 3

750, such as the Siemens/EPCOS B57620C103J062. In this case, the values for the external network are given by:

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

R1 = 9.76k R2 = 28k

Thevenin impedance from V including R4, if present.

to GND 100kΩ or less,

TEMP

R3 = 0Ω

Disabling Thermistor Functions

However, the LTC4011 will operate with other NTC therm istors having different nominal values or exponential temperature coefﬁcients. For these thermistors, the design equations for the resistors in the external network are:

Temperature sensing is optional in LTC4011 applications.

For low cost systems where temperature sensing may not be required, the V

pin may simply be wired to

TEMP

VRT to disable temperature qualiﬁcation of all charging

4011fb

Page 18

LTC4011

applicaTions inForMaTion

operations. 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

to VRT if the pause function is

TEMP

still desired.

INTVDD 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 INTVDD may reduce the accuracy of internal analog circuits used to monitor and terminate fast charging. In addition, DC current drawn from the INTVDD pin can greatly increase internal power dissipation at elevated VCC voltages. A minimum ceramic bypass capacitor of 0.1µF is recommended.

Calculating Average Power Dissipation

The user should ensure that the maximum rated IC junction temperature is not exceeded under all operating conditions. The thermal resistance of the LTC4011 package (θJA) is 38°C/W, provided the exposed metal pad is properly soldered to the PCB. The actual thermal resistance 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 PD (in watts) of the LTC4011 under normal operating conditions.

where:

= Average external INTVDD load current, if any

= Load current drawn by the external thermistor

VRT

network from V

= Gate charge of external P-channel MOSFET

TGATE

, if any

in coulombs

= Gate charge of external N-channel MOSFET

BGATE

(if used) in coulombs

= Maximum external LED forward voltage

LED

= External LED current-limiting resistor used in

LED

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 Ap plication 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 ﬁgures

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 component 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 mini

m 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

provides a bias current of (V

BAT

– V

ZENER

of Q4. R5

)/(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

thermistor network allows the

TEMP

LTC4011 to accurately terminate fast charge under a variety

of applied charge rates. Use of a synchronous PWM topol og

y improves efﬁciency and lowers power dissipation.

4011fb

Page 19

applicaTions inForMaTion

0.1µF

10µF

10µH

FAULT

INFET

CHRG

FROM

ADAPTER

12V

TOC READY

0.033µF 0.068µF

20µF

0.1µF

4.7µH

20µF

FAULT CHRG TOC READY

FROM

ADAPTER

12V

Figure 6. Minimum 1A LTC4011 Application

LTC4011

A full-featured 2A LTC4011 application is shown in Figure 8. FET-based PowerPath allows for maximum input voltage range from the DC adapter. The inherent voltage ratings of the V

CELL

, V

, SENSE and BAT pins allow charging

CDIV

Figure 7. 3A NiMH Charger with Full PowerPath Control

of one to sixteen series nickel cells in this application, governed only by the V cussed. The application includes all average cell voltage

overhead limits previously dis-

and battery temperature sensing circuitry required for the LTC4011 to utilize its full range of charge qualiﬁcation, safety monitoring and fast charge termination features. LED D1 indicates valid DC input voltage and installed battery, while LEDs D2 and D3 indicate charging. LED D4 indicates fault conditions. The grounded CHEM pin selects the NiMH charge termination parameter set.

4011fb

Page 20

LTC4011

0.1µF

D1 D2 D3 D4

10µF

6.8µH

10µF

FROM

ADAPTER

12V

FAULT

INFET

CHRG TOC READY

0.1µF

10µF

22µH

NiMH PACK WITH 10k NTC (1Ahr)

FAULT CHRG TOC READY

PAUSE

FROM

MCU

INFET

FROM

ADAPTER

24V

applicaTions inForMaTion

While the LTC4011 is a complete, standalone solution, Figure 9 shows that it can also be interfaced to a host microprocessor. The host 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 could be chosen as well.

→ V

) parameters

Figure 8. Full-Featured 2A LTC4011 Application

Figure 9. LTC4011 with MCU Interface

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Page 21

applicaTions inForMaTion

LTC4011

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 reli ably per be implemented.

form this function, full PowerPath control should

In most applications, there should not be an external load on the battery during charge. 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 complete 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.

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 and is 500mV above BAT. The READY output is

rises above 4.25V

asserted

when the LTC4011 completes charge qualiﬁcation.

When the LTC4011 determines charging should begin, it starts a precharge cycle because V

is less than 900mV.

CELL

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.

When the precharge state timer expires, the LTC4011 begins fast charge if V

is greater than 900mV. The

CELL

PWM, charge timer and internal termination control are suspended if pause is asserted (V

< 200mV), but all

TEMP

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 greater than 1°C per minute.

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

fast charge cycle had lasted more than t

/12 minutes,

MAX

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

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

PROG

minutes with the CHRG and TOC

outputs continuously

asserted.

Finally, where the PWM is disabled but V

resume if V

the LTC4011 enters the automatic recharge state

CHRG and TOC

. The charge timer will be reset and fast charging will

CELL

drops below 1.325V. The LTC4011 enters

CELL

outputs are deasserted. The

remains asserted to monitor

CDIV

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 returned 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 provide customized information to an LTC4011-based charger, allowing a single design to service a wide range of application batteries. Assume the charger is designed to provide a maximum charge current of 800mA (R

125mΩ). Figure 11 shows a 4-cell NiCd battery pack for which 800mA represents a 0.75C rate. When connected to the charger, this pack would provide battery tempera ture information and correctly conﬁgure both fast charge

termination parameters and time limits for the internal NiCd cells.

MAX

SENSE

4011fb

Page 22

LTC4011

(PAUSE)

READY

CHRG

TOC

1200mAhr NiCd CELLS

BATTERY

PACK

TEMP

CHEM

TIMER

66.5k

4011 F11

–

10k NTC

1500mAhr NiMH CELLS

BATTERY

PACK

TEMP

CELL

CHEM

4011 F12

–

10k NTC

applicaTions inForMaTion

Figure 10. Charging Waveforms Example

Figure 11. NiCd Battery Pack with Time Limit Control

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 that programs the correct number of series cells when it is connected to the charger, along with indicating chemistry 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. Charging parallel cells is not recommended.

Figure 12. NiMH Battery Pack Indicating Number of Cells

PCB Layout Considerations

To prevent magnetic and electrical ﬁeld radiation and high frequency resonant problems, proper layout of the components 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. Layout the PCB using this speciﬁc order.

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

4011fb

Page 23

4011 F13

BAT

HIGH

FREQUENCY

CIRCULATING

PATH

BAT

SWITCH NODE

SWITCHING GROUND

OUT

SENSE

4011 F14

DIRECTION OF CHARGING CURRENT

SENSE

BAT

applicaTions inForMaTion

LTC4011

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 switching 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.

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.

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 in ductance, which further improves EMI performance.

12. For best current programming accuracy, provide a Kelvin connection from R

to SENSE and BAT.

SENSE

See Figure 14 for an example.

13. It is important to minimize parasitic capacitance on the TIMER, SENSE and BAT pins. The traces connecting these pins to their respective resistors should be as short as possible.

Figure 13. High Speed Switching Path

Figure 14. Kelvin Sensing of Charge Current

4011fb

Page 24

LTC4011

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)

1 3 45678 9 10

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

package DescripTion

FE Package

20-Lead Plastic TSSOP (4.4mm)

(Reference LTC DWG # 05-08-1663)

Exposed Pad Variation CB

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Page 25

LTC4011

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER

B 01/10 Changes

Updated Order Information Section Changes to Electrical Characteristics Changes to Operation Section Changes to Applications Information

Changes

to Typical Application

to Figures 6, 7, 8, 9

(Revision history begins at Rev B)

1 2

2, 3, 4

12, 13, 14

15, 16, 19,

21, 22 19, 20

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

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Page 26

LTC4011

relaTeD parTs

PART NUMBER DESCRIPTION COMMENTS

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

LT1511 3A

LT1513 SEPIC

LTC1760 Smart

LTC1960 Dual Battery Charger/Selector with SPI 11-Bit V-DAC, 0.8% Voltage Accuracy, 10-Bit I-DAC, 5% Current Accuracy

LTC4008 High

LTC4010 High

LTC4060 Standalone

LTC4100 Smart

LTC4150 Coulomb

LTC4411 2.6A

LTC4412/ LTC4412HV

LTC4413 Dual

ThinSOT is a trademark of Linear Technology Corporation.

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

Constant- or Programmable-Current/Constant-

Voltage Battery Charger

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

Efﬁciency, Programmable Voltage/Current Battery

Charger

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

Linear NiMH/NiCd Fast Charger Complete NiMH/NiCd Charger in a Small Leaded or Leadless 16-Pin

Battery Charger Controller Level 2 Charger Operates with or without MCU Host, SMBus Rev. 1.1

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

Low Loss Ideal Diode No External MOSFET, Automatic Switching Between DC Sources,

Low

Loss PowerPath Controllers Very Low Loss Replacement for Power Supply ORing Diodes Using

2.6A, 2.5V to 5.5V, Ideal Diodes Low Loss Replacement for ORing Diodes, 100mΩ On Resistance

NiMH and NiCd Batteries

Charger Input Voltage May be Higher, Equal to or Lower than Battery Voltage, 500kHz Switching Frequency

Batteries, SMBus Rev 1.1 Compliant

Constant-Current/Constant-Voltage Current Programming, AC Adapter Current Limit and Thermistor Sensor and Indicator Outputs

Switching Regulator

Package, No Sense Resistor or Blocking Diode Required

Compliant

Simpliﬁed, 140mΩ On Resistance, ThinSOT™ Package

Minimal External Components, 3V ≤ VIN ≤ 28V, (3V ≤ VIN ≤ 36V for HV)

Switching Regulator, Resistor Voltage/

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear.com

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LT 0110 REV B • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 2005