LTC6804-1/LTC6804-2
59
680412fc
For more information www.linear.com/LTC6804-1
applicaTions inForMaTion
FULLY ISOLATED POWER
A simple DC/DC flyback converter can provide isolated
power for an LTC6804 from a remote 12V power source
as shown in Figure 30. This circuit, along with the isoSPI
transformer isolation, results in LTC6804 circuitry that is
completely floating and uses almost no power from the
batteries. Aside from reducing the amount of circuitry
that operates at battery potential, such an arrangement
prevents battery load imbalance. The LTC6804 watchdog
timer requires V
REG
power to timeout. Therefore, care
must be taken to allow the LTC6804 to timeout first before
removing V
REG
power; otherwise the LTC6804 will not
enter sleep mode. A diode should be added between the
V+ and the top cell being monitored. This will prevent any
Figure 30. Powering LTC6804 from a Remote 12V Source
TEMPERATURE (°C)
–40 0
V
TEMPx
(% V
REF2
)
80
60
40
20
90
70
50
30
10
0
–20 20 6040 80
10k
NTC
10k AT 25°C
V
–
V
REF2
V
TEMP
DRIVE
V
REG
V
–
V
+
LTC6804
100nF
100V
CMHZ5265B
62V
NSV1C201MZ4
CMHD459A
PA0648NL
CMMSH1-40
GND
EN/UVLO
R
FB
LT8300
130k
100Ω
SW
V
IN
1µF
10V
4.7µF
25V
7
2
8
1
5
4
1µF
100V
22.1k
100k
12V
52V
13V
RETURN
4.7µF
25V
•
•
•
CONNECT TO TOP CELL
current from conducting through internal parasitic paths
inside the IC when the isolated power is removed.
READING EXTERNAL TEMPERATURE PROBES
Figure 31 shows the typical biasing circuit for a negative-
temperature-coefficient (NTC) thermistor. The 10kΩ at 25°C
is the most popular sensor value and the V
REF2
output stage
is designed to provide the current required to directly bias
several of these probes. The biasing resistor is selected
to correspond to the NTC value so the circuit will provide
1.5V at 25°C (V
REF2
is 3V nominal). The overall circuit
response is approximately –1%/°C in the range of typical
cell temperatures, as shown in the chart of Figure 31 .
Figure 31. Typical Temperature Probe Circuit and Relative Output
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