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LTC4010

4010fb

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 bat-

tery. In this configuration, the LTC4010 relies expressly

on the ability of the host MCU to know when load tran-

sients 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, the battery should

be disconnected from the load with a rectifier or switch

when charging. 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 LTC4010 to prematurely terminate a

charge cycle and/or prematurely restart a fast charge. In

this case, it may be necessary to inhibit the LTC4010 after

charging is complete until external gas gauge circuitry

indicates that recharging is necessary. Shutdown power

is applied to the LTC4010 through the body diode of the

P-channel MOSFET in this application.

applicaTions inForMaTion

Waveforms

Sample waveforms for a standalone application during

a typical charge cycle are shown in Figure 9. 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 LTC4010 during a typical charge cycle.

Initially, the LTC4010 is in low power shutdown as the

system operates from a heavily discharged battery. A DC

adapter is then connected such that VCC rises above 4.25V

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

when the LTC4010 completes charge qualification.

When the LTC4010 determines charging should begin, it

starts a precharge cycle because VCELLislessthan900mV.

As long as the temperature remains within prescribed

limits, the LTC4010 charges (TGATE switching), applying

limited current to the battery with the PWM in order to

bring the average cell voltage to 900mV.

Figure 9. Charging Waveforms Example

SHDN

VCC ≥ BAT + 500mV

VCC < BAT + 25mV

VCC

READY

VCDIV

TGATE

VCELL

CHRG

VTEMP

(PAUSE)

SHDN

TOP-OFF

AUTO

RECHARGE

FAST CHARGE

PRECHARGE

0.9V

EXTERNAL

PAUSE

200mV

4010 F09

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