DS2740 Просмотр технического описания (PDF) - Maxim Integrated

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DS2740

High-Precision Coulomb Counter

Maxim Integrated 

DS2740

POWER MODES

The DS2740 has two power modes: Active and Sleep. While in Active mode, the DS2740 operates as a

high-precision coulomb counter with current and accumulated current measurement blocks operating

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

allowed to all registers. PIO pin is active. In Sleep mode, the DS2740 operates in a low-power mode with

no current measurement activity. Serial access to current, accumulated current, and status/control

registers is allowed if VDD > 2V.

The DS2740 operating mode transitions from SLEEP to ACTIVE when:

1) DQ > VIH, and VDD > UV threshold, or

2) VDD rises from below UV threshold to above UV threshold.

The DS2740 operating mode transitions from ACTIVE to SLEEP when:

1) VDD falls to UV threshold, or

2) SMOD = 1 and DQ < VIL for 2s.

CURRENT MEASUREMENT

In the Active mode of operation, the DS2740 continually measures the current flow into and out of the

battery by measuring the voltage drop across a low-value current-sense resistor, RSNS. To extend the input

range for pulse-type load currents, the voltage signal can be filtered by adding a capacitor between the

IS1 and IS2 pins. The external capacitor and two internal resistors form a lowpass filter at the input of the

ADC. The voltage-sense range at IS1 and IS2 is ±51.2mV. The input converts peak signal amplitudes up

to 102mV as long as the continuous or average signal level (post filter) does not exceed ±51.2mV over

the conversion cycle period. The ADC samples the input differentially at IS1 and IS2 with an 18.6kHz

sample clock and updates the current register at the completion of each conversion cycle. Conversion

times for each resolution option are listed in the tables below. Two resolution options are available.

Figure 3 describes the current measurement register format and resolution for each option. “S” indicates

the sign bit(s).

Figure 3. CURRENT REGISTER FORMAT

DS2740U: Units: 1.5625μV/RSNS, 15-bit + sign resolution, 3.5s conversion period.

DS2740BU: Units: 6.250μV/RSNS, 13-bit + sign resolution, 0.875s conversion period.

MSB—Address 0Eh

LSB—Address 0Fh

S 214 213 212 211 210 29 28

MSb

LSb

Full-scale magnitude: ±51.2mV

27 26 25 24 23 22 21 20

MSb

LSb

5 of 16

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