LTC4010CFE datasheet(20/24 Pages) LINER

20 / 24 page

LTC4010

4010fb

When the precharge state timer expires, the LTC4010

begins fast charge if VCELL is greater than 900mV. The

PWM, charge timer and internal termination control are

suspended if pause is asserted (VTEMP < 200mV), but all

statusoutputscontinuetoindicatechargingisinprogress.

The fast charge state continues until the selected voltage

or temperature termination criteria are met. Figure 9 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 tMAX/12 minutes,

the LTC4010 begins a top-off charge with a current of

IPROG/10. Top-off is an internally timed charge of tMAX/3

minutes with the CHRG output continuously asserted.

Finally, the LTC4010 enters the automatic recharge state

wheretheCHRGoutputisdeasserted.ThePWMisdisabled

but VCDIV remains asserted to monitor VCELL. The charge

timer will be reset and fast charging will resume if VCELL

drops below 1.325V. The LTC4010 enters 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 9,

temperature qualification is an ongoing part of the charg-

ing process, if an external thermistor network is detected

by the LTC4010. Should prescribed temperature limits be

exceeded during any particular charging state, charging

wouldbesuspendeduntilthesensedtemperaturereturned

to an acceptable range.

Battery-Controlled Charging

BecauseoftheprogrammingarrangementoftheLTC4010,

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 LTC4010-based

charger, allowing a single design to service a wide range

of application batteries. Assume the charger is designed

toprovideamaximumchargecurrentof800mA(RSENSE =

125mΩ). Figure 10 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.

applicaTions inForMaTion

A second possibility is to configure an LTC4010-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 LTC4010 detection of battery insertion

or removal. Figure 11 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.

Anyofthesebatterypackchargecontrolconceptscouldbe

combinedinavarietyofwaystoservicecustomapplication

needs. Charging parallel cells is not recommended.

PCB Layout Considerations

To prevent magnetic and electrical field radiation and

high frequency resonant problems, proper layout of the

components connected to the LTC4010 is essential. Refer

to Figure 12. 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.

Figure 10. NiCd Battery Pack with Time Limit Control

1200mAhr

NiCd CELLS

BATTERY

PACK

VTEMP

CHEM

TIMER

66.5k

4010 F10

–

10k

NTC

Figure 11. NiMH Battery Pack Indicating Number of Cells

1500mAhr

NiMH CELLS

BATTERY

PACK

VTEMP

VCELL

CHEM

4010 F11

–

10k

NTC

LTC4010CFE Datasheet(PDF) 20 Page - Linear Technology

LTC4010CFE Datasheet(HTML) 20 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL