Linear Technology LTC6804-1 - Current Measurement with a Hall Effect Sensor; Current Measurement with a Shunt Resistor

LTC6804-1/LTC6804-2
66
680412fc
For more information www.linear.com/LTC6804-1
applicaTions inForMaTion
CURRENT MEASUREMENT WITH A HALL EFFECT
SENSOR
The LTC6804 auxiliary ADC inputs (GPIO pins) may be
used for any analog signal, including those from various
active sensors that generate a compatible voltage. One
such example that may be useful in a battery management
setting is the capture of battery current. Hall-effect sensors
are popular for measuring large battery currents since the
technology provides a non-contact, low power dissipation
solution. Figure 38 shows schematically a typical Hall
sensor that produces two outputs that proportion to the
V
CC
provided. The sensor is powered from a 5V source
Figure 38. Interfacing a Typical Hall-Effect Battery
Current Sensor to Auxiliary ADC Inputs
and produces analog outputs that are connected to GPIO
pins or inputs of the MUX application shown in Figure 32.
The use of GPIO1 and GPIO2 as the ADC inputs has the
possibility of being digitized within the same conversion
sequence as the cell inputs (using the ADCVAX com
-
mand), thus synchronizing cell voltage and cell current
measurements.
C
URRENT MEASUREMENT WITH A SHUNT RESISTOR
It is possible to measure the battery current on the LTC6804
GPIO pins with a high performance current sense ampli
-
fier and a shunt. Figure 39 shows 2 LTC6102s being
used to measure the discharge and charge currents on a
12-
cell batter
y stack. To achieve a large dynamic range
while maintaining a high level of accuracy the LTC6102
is required. The circuit shown is able to accurately mea
-
sure ±
200Amps to 0.1Amps. The offset of the
LTC6102
will only contribute a 20mA error. To maintain a very low
sleep current the V
DRIVE
is used to disable the LTC6102
circuits so that they draw no current when the LTC6804
goes to sleep.
CHARGER
–
+
–
+
+
–
+
–
L
O
A
D
V
OUT D
= I
DISCHARGE
• R
SENSE
( )
WHEN I
DISCHARGE
≥ 0DISCHARGING:
R
OUT(D)
R
IN(D)
V
OUT C
= I
CHARGE
• R
SENSE
( )
WHEN I
CHARGE
≥ 0CHARGING:
R
OUT(C)
R
IN(C)
680412 F39
V
BATTSTACK
R
IN(D)
100Ω
LTC6102
LTC6804 V
–
LTC6804 V
–
V
DRIVE
V
DRIVE
R
IN(C)
100Ω
R
IN(D)
100Ω
LTC6102
LTC6804 V
+
V
OUT(C)
R
OUT(C)
4.02k
R
OUT(D)
4.02k
V
OUT(D)
GPIO 1GPIO 2
R
IN(C)
100Ω
I
CHARGE
R
SENSE
0.5mΩ
I
DISCHARGE
V
+
V
–
OUT
–INS+IN
V
+
V
–
OUT
–INS +IN
–INF –INF
V
REG
0.1µF
V
REG
0.1µF
1µF1µF
Figure 39. Monitoring Charge and Discharge Currents with a LTC6102
680412 F38
LEM DHAB
CH2 ANALOG → GPIO2
V
CC
5V
GND ANALOG_COM → V
–
CH1 ANALOG0 → GPIO1
A
B
C
D