DS2437 데이터 시트보기 (PDF) - Dallas Semiconductor -> Maxim Integrated

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DS2437

Smart Battery Monitor

Dallas Semiconductor -> Maxim Integrated 

DS2437

Voltage is expressed in this register in scaled binary format, as outlined in Table 2. Note that while codes

exist for values below 2.7V, accuracy of the ADC and the limitation on the DS2437’s supply voltage

make it unlikely that these values would be used in actual practice. See “Memory Map” section for the

VOLTAGE REGISTER address location.

Voltage/Data Relationships Table 2

BATTERY

VOLTAGE

0.01V

2.7

3.6V

5V

7.2V

9.99V

10V

DIGITAL OUTPUT (Binary)

0000 0000 0000 0001

0000 0001 0000 1110

0000 0001 0110 1000

0000 0001 1111 0100

0000 0010 1101 0000

0000 0011 1110 0111

0000 0011 1110 1000

DIGITAL OUTPUT (Hex)

0001h

010Eh

0168h

01F4h

02D0h

03E7h

03E8h

For applications requiring a general purpose voltage A/D converter, the DS2437 can be configured so that

the result of a Convert V command will place the scaled binary representation of the voltage on the VAD

input (as opposed to the VDD input) into the VOLTAGE REGISTER in the same format described in

Table 2. Depending upon the state of the configuration register, either (but not both) the VDD or VAD

voltage will be stored in the VOLTAGE REGISTER upon receipt of the Convert V command. Refer to

the description of the Configuration Register in the Memory Map section for details. If the VAD input is

used as the voltage input, the A/D will be accurate for 0V < VAD < 2VDD over the range 2.7V < VDD <

5.0V. Recall that the battery voltage A/D (VDD input) loses accuracy as VDD falls below 2.7V. This

feature gives the user the ability to have a voltage A/D that meets spec accuracy for inputs over the entire

range of 0V < VAD < 10V for VDD = 5.0V.

OPERATION – MEASURING BATTERY CURRENT

The DS2437 features a sigma-delta A/D converter that effectively measures the current flow into and out

of the battery pack. It does so in the background at a rate of 32 measurements/sec; thus, no command is

required to initiate current flow measurements. However, the DS2437 will only perform current A/D

measurements if the IAD bit is set to 1 in the CONFIGURATION REGISTER. The DS2437 measures

current flow in and out of the battery through the VSENS pins; the voltage from the VSENS+ pin to the

VSENS- pin is considered to be the voltage across the current sense resistor, RSENS. While the VSENS+

terminal may be tied directly to the cell side of the RSENS resistor, we recommend using an RC low pass

filter between the other side of RSENS and VSENS-. Using a 47 kΩ=(max) resistor (RF) and a 0.1 µF

capacitor (CF), the filter cutoff is approximately 32 Hz. The current A/D measures at a rate of 32 times

per second, or once every 31.25 ms. This filter will capture the effect of many current spikes and will thus

allow the current accumulators to accurately reflect the total charge which has gone into or out of the

battery.

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