DS2745U 查看數據表（PDF） - Maxim Integrated

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DS2745U

Low-Cost I2C Battery Monitor

Maxim Integrated 

DS2745 Low-Cost I2C Battery Monitor

POWER MODES

The DS2745 operates in one of two power modes: active and sleep. While in active mode, the DS2745 operates as

a high-precision battery monitor with voltage, temperature, current and accumulated current measurements

acquired continuously and the resulting values updated in the measurement registers. Read and write access is

allowed to all registers.

In sleep mode, the DS2745 operates in a low-power mode with no measurement activity. Serial access to current,

accumulated current, and status/control registers is allowed in sleep mode if VDD > 2V.

The DS2745 operating mode transitions from SLEEP to ACTIVE when:

SDA > VIH OR SCL > VIH

The DS2745 operating mode transitions from ACTIVE to SLEEP when:

SMOD = 1 AND (SDA < VIL AND SCL < VIL) for tSLEEP.

CAUTION: If SMOD = 1, pull-up resistors are required on SCL and/or SDA in order to ensure that the DS2745

transitions from SLEEP to ACTIVE mode when the battery is charged. If the bus is not pulled up, the DS2745

remains in SLEEP and cannot accumulate the charge current. This caution statement applies particularly to on a

battery that is charged on a standalone charger.

VOLTAGE MEASUREMENT

Battery voltage is measured at the VIN input with respect to VSS over a range of 0 to 4.992V (VIN pin is limited to

VDD voltage) and with a resolution of 4.88mV. The result is updated every 440ms and placed in the VOLTAGE

register in two’s compliment form. Voltages above the maximum register value are reported as 7FFFh.

Figure 4. VOLTAGE REGISTER FORMAT

MSB—Address 0C

S 29 28 27 26 25

MSb

“S”: sign bit(s), “X”: reserved

24 23

LSb

LSB—Address 0D

22 21 20 X X X X X

MSb

LSb

Units: 4.88mV

The input impedance of VIN is sufficiently large (>15M) to be connected to a high impedance voltage divider in

order to support multiple cell applications. The pack voltage should be divided by the number of series cells to

present a single cell average voltage to the VIN input. Note that the first voltage measurement made after the

DS2745 is powered or after the ACR register is written will not be valid. The host should wait one measurement

cycle after either of these two conditions occur before reading voltage.

TEMPERATURE MEASUREMENT

The DS2745 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C.

Temperature measurements are updated every 440ms and placed in the Temperature Register in two’s

complement form.

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