LTC6802-1_1 LINER [Linear Technology], LTC6802-1_1 Datasheet - Page 30

• Manufacturer Part Number: LTC6802-1_1
• Description: Multicell Battery Stack Monitor
• Manufacturer: LINER [Linear Technology]

LTC6802-1
APPLICATIONS INFORMATION
Cell-Voltage Filtering
The LTC6802-1 employs a sampling system to perform
its analog-to-digital conversions and provides a conver-
sion result that is essentially an average over the 0.5ms
conversion window, provided there isn’t noise aliasing with
respect to the delta-sigma modulator rate of 512kHz. This
indicates that a lowpass filter with useful attenuation at
500kHz may be beneficial. Since the delta-sigma integra-
tion bandwidth is about 1kHz, the filter corner need not
be lower than this to assure accurate conversions.
Series resistors of 100Ω may be inserted in the input
paths without introducing meaningful measurement
error, provided only external discharge switch FETs are
being used. Shunt capacitors may be added from the cell
inputs to V
Note that this filtering is not compatible with use of the
internal discharge switches to carry current since this
would induce settling errors at the time of conversion as
any activated switches temporarily open to provide Kelvin
mode cell sensing. As a discharge switch opens, cell wiring
resistance will also form a small voltage step (recovery
of the small IR drop), so keeping the frequency cutoff of
the filter relatively high will allow adequate settling prior
to the actual conversion. A guard time of about 60μs is
provided in the ADC timing, so a 16kHz LP is optimal and
offers about 30dB of noise rejection.
No resistor should be placed in series with the V
Because the supply current flows from the V
resistance on this pin could generate a significant conver-
sion error for CELL1.
30
Figure 13. Adding RC Filtering to the Cell Inputs
(One Cell Connection Shown)
–
, creating RC filtering as shown in Figure 13.
100Ω
100Ω
100nF
100nF
7.5V
C(n)
S(n)
C(n – 1)
68021 F13
–
pin, any
–
pin.
The V
monitored cell group. A decoupling network of 20Ω /100nF
is recommended.
READING EXTERNAL TEMPERATURE PROBES
Using Dedicated Inputs
The LTC6802-1 includes two channels of ADC input, V
and V
(tempco about –4%/°C generally) or diodes (–2.2mV/°C
typical) located within the cell array. Sensors can be
powered directly from V
60μA total).
For sensors that require higher drive currents, a buffer op
amp may be used as shown in Figure 15. Power for the
sensor is actually sourced indirectly from the V
Figure 15. Buffering V
+
TEMP2
Figure 14. Driving Thermistors Directly from V
pin is powered from the top cell potential of the
LTC6802-1
LTC6802-1
, that are intended to monitor thermistors
V
V
TEMP2
TEMP1
V
V
V
V
TEMP2
TEMP1
REG
REF
V
NC
V
V
REG
REF
NC
−
V
−
REF
REF
for Higher-Current Sensors
as shown in Figure 14 (up to
1μF
+
–
LT6000
1μF
NTC
10k
100k
10k
100k
NTC
68021 F14
NTC
10k
REF
100k
68021 F15
10k
100k
NTC
REG
TEMP1
68021fa
pin