ltc6803g-3 Linear Technology Corporation, ltc6803g-3 Datasheet - Page 37

• Manufacturer Part Number: ltc6803g-3
• Description: Ltc6803-1/ltc6803-3 - Multicell Battery Stack Monitor
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
the LTC6803-1 and LTC6803-3 were chosen to facilitate
this physical separation. There is no more than 5.5V
between any two adjacent pins. The package body is used
to separate the highest voltage (e. g., 43.2V) from the low-
est voltage (0V). As an example, Figure 27 shows the DC
voltage on each pin with respect to V
battery cells are connected to the LTC6803-3.
ADVANTAGES OF DELTA-SIGMA ADCS
The LTC6803 employs a delta-sigma analog-to-digital
converter for voltage measurement. The architecture of
delta sigma converters can vary considerably, but the
common characteristic is that the input is sampled many
times over the course of a conversion and then filtered or
averaged to produce the digital output code. In contrast,
a SAR converter takes a single snapshot of the input
voltage and then performs the conversion on this single
sample. For measurements in a noisy environment, a
delta sigma converter provides distinct advantages over
a SAR converter.
Figure 27. Typical Pin Voltages for Twelve 3.6V Cells
–
when twelve 3.6V
42.5V
42.5V
42.5V
43.2V
43.2V
43.2V
39.6V
39.6V
32.4V
32.4V
28.8V
28.8V
25.2V
25.2V
14.4V
14.4V
21.6
21.6
36V
36V
18V
18V
CSBO
SDOI
SCKO
V
C12
S12
C11
S11
C10
S10
C9
S9
C8
S8
C7
S7
C6
S6
C5
S5
C4
S4
+
LTC6803-3
While SAR converters can have high sample rates, the full-
power bandwidth of a SAR converter is often greater than
1MHz, which means the converter is sensitive to noise out
to this frequency. And many SAR converters have much
higher bandwidths—up to 50MHz and beyond. It is pos-
sible to filter the input, but if the converter is multiplexed
to measure several input channels a separate filter will be
required for each channel. A low frequency filter cannot
reside between a multiplexer and an ADC and achieve a
high scan rate across multiple channels. Another conse-
quence of filtering a SAR ADC is that any noise reduction
gained by filtering the input cancels the benefit of having
a high sample rate in the first place, since the filter will
take many conversion cycles to settle.
For a given sample rate, a delta-sigma converter can
achieve excellent noise rejection while settling completely
in a single conversion—something that a filtered SAR con-
verter cannot do. Noise rejection is particularly important
in high voltage switching controllers, where switching
noise will invariably be present in the measured voltage.
V
V
V
GPIO2
GPIO1
WDTB
TEMP2
TEMP1
680313 F27
MODE
V
CSBI
SCKI
V
SDO
TOS
REG
SDI
REF
NC
C0
S1
C1
S2
C2
S3
C3
V
–
0V TO 5.5V
0V TO 5.5V
0V TO 5.5V
0V TO 5.5V
0V TO 5.5V
0V TO 5.5V
0V TO 5.5V
0V TO 5.5V
0V TO 5.5V
5V
3.1V
1.5V
1.5V
0V
0V
0V
3.6V
3.6V
7.2V
7.2V
10.8V
10.8V
LTC6803-1/LTC6803-3
37
680313f