LTC6802IG-2 LINER [Linear Technology], LTC6802IG-2 Datasheet - Page 26

• Manufacturer Part Number: LTC6802IG-2
• Description: Multicell Addressable Battery Stack Monitor
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
LTC6802-2
Internal Protection Diodes
Each pin of the LTC6802-2 has protection diodes to help
prevent damage to the internal device structures caused
by external application of voltages beyond the supply rails
as shown in Figure 9.
The diodes shown are conventional silicon diodes with a
forward breakdown voltage of 0.5V. The unlabeled Zener
diode structures have a reverse-breakdown characteristic
which initially breaks down at 12V then snaps back to a 7V
clamping potential. The Zener diodes labeled Z
higher voltage devices with an initial reverse breakdown

V
C12
S12
C11
S11
C10
S10
C9
S9
C8
S8
C7
S7
C6
S6
C5
S5
C4
S4
C3
S3
C2
S2
C1
S1
V
+
–
Figure 9. Internal Protection Diodes
Z
Z
Z
CLAMP
CLAMP
CLAMP
LTC6802-2
V
CLAMP
GPIO2
GPIO1
WDTB
MODE
MMB
CSBI
SCKI
SDO
TOS
SDI
68022 F09
A3
A2
A1
A0
are
of 30V snapping back to 25V. The forward voltage drop
of all Zeners is 0.5V. Refer to this diagram in the event of
unpredictable voltage clamping or current flow. Limiting
the current flow at any pin to ±10mA will prevent damage
to the IC.
Cell-Voltage Filtering
The LTC6802-2 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.
Figure 10. Adding RC Filtering to the Cell Inputs
(One Cell Connection Shown)
+
–
, creating RC filtering as shown in Figure 10.
100
100
100nF
100nF
6.2V
Cn
Sn
Cn – 1
68021 F10
68022fa