DS2715 查看數據表（PDF） - Maxim Integrated

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DS2715

NiMH Battery Pack Charge Controller

Maxim Integrated 

DS2715: NiMH Battery Pack Charge Controller

Figure 3. Ideal Comparator Input and Charge Control Output Waveforms

VCH

Not drawn to scale

VPullup

|Vsns|

VOL

|VFC|

|Vsns(DC)|

Time

|VFC + VHYS-FC|

Charge Rate Selection

The charge rate is determined by an external sense resistor connected between the SNS+ and SNS- pins. The

DS2715 will regulate the charge current to maintain a voltage drop of VFC (or VFC + 0.5 x VHYS-FC in comparator

mode) across the sense resistor during FAST-CHARGE. The sense resistor can therefore be selected by:

Linear Mode:

R = |VFC / Desired FAST-CHARGE Current|

Comparator Mode:

R = |(VFC + 0.5 x VHYS-FC) / Desired FAST-CHARGE Current|

Timeout Selection

The various charge modes employ different timers to ensure reliable and safe charging. PRECHARGE has a fixed

30 minute limit generated by an internal oscillator. A fault is generated if this time limit is exceeded. FAST-

CHARGE mode normally operates until its dT/dt termination scheme activates. In the event that the dT/dt sensing

does not perform correctly, a safety timeout is required. This timeout is set by an external resistor on the Rt pin to

VSS and provides secondary protection against significant overcharging. As such, the value of the Rt resistor

should be chosen so that the timeout is greater than the FAST-CHARGE time expected in the application, but not

so much greater that its protection is compromised. If the timer expires during FAST-CHARGE, the timer count is

reset and charging proceeds to the TOPOFF charge phase. The Rt resistor also sets the timed charge duration of

TOPOFF mode. The TOPOFF time-out period is fixed at half (a quarter for the DS2715B) of the FAST-CHARGE

time-out period. When the timer expires in TOPOFF, the DS2715 enters the DONE state.

Resistors can be selected to support fast-charge time-out periods of 0.5 to 6 hours and TOPOFF charge time-out

periods of 0.25 to 3 hours (0.125 to 1.5 hours for the DS2715B). The programmed FAST-CHARGE time

approximately follows the equation:

t(minutes) = 1.5 x R(ohms) / 1000

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