DS2441 Ver la hoja de datos (PDF) - Dallas Semiconductor -> Maxim Integrated

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DS2441

1-Cell Li-Ion Battery Manager

Dallas Semiconductor -> Maxim Integrated 

DS2441

from DQ when this bit is set, DQ must subsequently remain high to support this mode of operation. A

high-to-low transition on DQ clears the RFSH bit.

Refreshing Undervoltage Packs. To charge severely undervoltage DS2441-based battery packs, apply a

charger to the pack and read the Status Register to check the value of the UV bit. If UV=1, set the RFSH

bit to logic 1 and pull DQ high to function as the DS2441’s power supply. The DS2441 draws power

from DQ and allows charging to occur as long as DQ remains high and no charge protection condition

arises. To periodically check whether the undervoltage condition remains, read the Status Register to

check the value of UV. (The first high-to-low transition on DQ during the Status Register read will clear

the RFSH bit. If the undervoltage condition remains, as soon as the RFSH bit is cleared the DS2441 will

return to Low Power Mode, disabling charging.) If UV is still logic 1, set RFSH to logic 1 and pull DQ

high to continue charging. Loop in this manner until UV=0. When UV is low, the DS2441 will be in its

normal operating mode and will support normal charging.

CURRENT MEASUREMENT

The DS2441 measures current flow into and out of the battery pack by measuring the voltage across sense

resistor RSENS connected between the PACK- terminal of the battery pack and the negative terminal of the

battery. To accomplish this, the GND pin on the DS2441 is connected to the negative terminal of the

battery and the ISENS pin is connected, through a low-pass filter, to the PACK- terminal of the pack. To

measure current, the DS2441 actually measures VISENS with respect to GND. In its normal mode of

operation, the DS2441 takes current measurements continuously with no assistance from the host system.

In Low Power Mode, the DS2441 suspends current measurements.

The DS2441 measures the voltage drop across RSENS using a digital sampling and accumulation scheme.

The use of an external low-pass filter with a corner frequency below 2 kHz on the VISENS pin is

recommended. The current is measured with a signed 11-bit (0.005C) resolution. The last completed

measurement is placed in the Current Register using a sign-extended, two’s-complement format. This

register is not updated while it is being read by the host system to ensure that only the last completed

conversion is read out. The Current Register is scaled such that a count of 20010 corresponds to a current

of 1C. Thus, the range of current flow that can be measured is from -5.115C (discharging) to +5.115C

(charging). The sign (S) of the current measurement, indicating charge or discharge, resides in the six

most significant bits of the Current Register, as shown in Figure 4. Some example Current Register

values are shown in Table 4.

CURRENT REGISTER FORMAT Figure 4

27 26 25 24 23 22 21 20 LSB

msb

(unit = 0.005C)

lsb

S S S S S S 29 28 MSB

8 of 29

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