Power modes, Current measurement, Figure 3. current register formats – Rainbow Electronics DS2740 User Manual
Page 4
DS2740
4 of 15
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 V
DD
> 2V.
The DS2740 operating mode transitions from SLEEP to ACTIVE when:
1)
DQ > V
IH
, and V
DD
> UV threshold, or
2)
V
DD
rises from below UV threshold to above UV threshold.
The DS2740 operating mode transitions from ACTIVE to SLEEP when:
1)
V
DD
falls to UV threshold, or
2)
SMOD = 1 and DQ < V
IL
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, R
SNS
. 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 75mV 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 FORMATS
DS2740: 15-bit + sign resolution, 3.5s conversion period.
MSB—Address 0E
LSB—Address 0F
S
2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSb
LSb
MSb
LSb
Units: 1.5625
mV/Rsns
DS2740B: 13-bit + sign resolution, 0.875s conversion period.
MSB—Address 0E
LSB—Address 0F
S
S
S
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSb
LSb
MSb
LSb
Units: 6.250
mV/Rsns