Ds 2 7 8 8, Stand-alone fuel-gauge ic with led display drivers, Temperature measurement – Rainbow Electronics DS2788 User Manual
Page 8: Current measurement
D
S
2
7
8
8
Temperature Measurement
The DS2788 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 (TEMP)
register in two’s complement form. Figure 4 shows the
format of the Temperature register.
Current Measurement
In the ACTIVE mode of operation, the DS2788 continu-
ally measures the current flow into and out of the bat-
tery by measuring the voltage drop across a low-value
current-sense resistor, R
SNS
. The voltage-sense range
between SNS and V
SS
is ±51.2mV. The input linearly
converts peak signal amplitudes up to 102.4mV as long
as the continuous signal level (average over the con-
version cycle period) does not exceed ±51.2mV. The
ADC samples the input differentially at 18.6kHz and
updates the Current (CURRENT) register at the com-
pletion of each conversion cycle.
The Current register is updated every 3.515s with the
current conversion result in two’s complement form.
Charge currents above the maximum register value are
reported at the maximum value (7FFFh = +51.2mV).
Discharge currents below the minimum register value
are reported at the minimum value (8000h = -51.2mV).
Stand-Alone Fuel-Gauge IC with
LED Display Drivers
8
_______________________________________________________________________________________
TEMP
READ ONLY
MSB—ADDRESS 0Ah
LSB—ADDRESS 0Bh
S
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
X
X
X
X
X
MSb
LSb
MSb
LSb
“S”: SIGN BIT(S), “X”: RESERVED
UNITS: 0.125
°C
Figure 4. Temperature Register Format
CURRENT
READ ONLY
MSB—ADDRESS 0Eh
LSB—ADDRESS 0Fh
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
“S”: SIGN BIT(S)
UNITS: 1.5625µV/R
SNS
Figure 5. Current Register Format
CURRENT RESOLUTION (1 LSB)
R
SNS
V
SS
- V
SNS
20m
15m
10m
5m
1.5625µV
78.13µA
104.2µA
156.3µA
312.5µA