DS2710G データシートの表示（PDF） - Maxim Integrated

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DS2710G

Single-Cell NiMH Charger

Maxim Integrated 

Single-Cell NiMH Charger

Charge-Current Regulation

The DS2710 regulates charge current by maintaining a

constant average voltage across an external sense

resistor connected between the VN1 and VN0 pins.

VN1 and VN0 drive an internal comparator in the

DS2710 to switch the CS output ON and OFF to drive a

regulating pnp bipolar or a pMOS transistor. Hysteresis

on the comparator input provides noise rejection. The

DS2710 regulates the charge current during FAST-

CHARGE to maintain a voltage drop across the sense

resistor as follows:

VSENSE = VIREF - 0.5 x VHYS-COMP = 0.113V (typ)

Figure 3 shows the sense resistor voltage and CS pin

voltage of the regulating circuit during normal operation.

Charging with Load Applied

NiMH cells have a low, but finite, impedance. If load

current is flowing out of the battery, an internal voltage

drop appears at the battery terminals. This can interfere

with the CTEST and -ΔV detection. If the load current is

variable, early termination is more likely than if the load

current is constant. If the load’s ground is connected to

the negative terminal of the cell (VN0), load current

flows through the current-sense resistor, resulting in less

charge current to the battery. The load-current return

path should be to charger ground to reduce the likeli-

hood of false termination or impedance-test errors.

Charging with load applied is not recommended.

Temperature Monitoring

Accurate temperature sensing is needed to detect tem-

perature FAULT conditions. Connecting an external

10kΩ NTC thermistor between THM and VSS and a

10kΩ bias resistor between VDD and THM allows the

DS2710 to sense temperature. To accurately monitor

the cell, the thermistor should make physical contact

either to the cell or cell tabs. Table 1 shows several rec-

ommended 10kΩ thermistors.

MIN, MAX Temperature Compare

The voltage thresholds of the THM input (VTHM-MIN,

VTHM-MAX) are set to allow charging to start if the ther-

mistor temperature is between 0°C and +45°C when

using the recommended 10kΩ bias resistor and 10kΩ

thermistor circuit. If precharging is in progress and the

voltage on THM reaches VTHM-STOP, precharging

stops and a FAULT condition is generated. If the volt-

age on THM reaches VTHM-STOP during FAST-

CHARGE or TOP-OFF, charging stops and the DS2710

enters the MAINTENANCE state. FAST-CHARGE and

Table 1. THM Thresholds

THM THRESHOLD

MIN

MAX

STOP

RATIO OF VCBIAS

0.73

0.33

0.29

THERMISTOR

RESISTANCE

(k
)

27.04

4.925

4.085

TEMPERATURE (°C)

Semitec 103AT-2

Fenwal

197-103LAG-A01,

173-103LAF-301

0

+4

+45

+42

+50

+47

NOT DRAWN TO SCALE

VOH1

VCS

VOL1

VIREF

VSENSE

VSENSE (DC)

TIME

VIREF - VHYS-COMP

Figure 3. Ideal Comparator Input and Charge Control Output

Waveforms

0.75

0.70

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0

DIVIDER OUTPUT

10

20

30

40

50

TEMPERATURE (°C)

Figure 4. Ratio of THM Pin to VDD Pin Over Temperature

8 _______________________________________________________________________________________

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