LTC6803-2_15 Datasheet, PDF (18/40 Pages) Linear Technology – Multicell Battery Stack Monitor

LTC6803-2/LTC6803-4
OPERATION
An example to calculate the PEC is listed in Table 1 and
Figure 4. The PEC of the 1 byte data 0x01 is computed as
0xC7 after the last bit of the byte streamed in. For multiple
byte data, PEC is valid at the end (LSB) of the last byte.
LTC6803 calculates PEC byte for any command or data
received and compares it with the PEC byte following the
command or data. The command or data is regarded as
valid only if the PEC bytes match. LTC6803 also attaches
the calculated PEC byte at the end of the data it shifts out.
Broadcast Commands: A broadcast command is one to
which all devices on the bus will respond, regardless of
device address. See the Bus Protocols and Commands
sections. With broadcast commands all devices can be
sent commands simultaneously. This is useful for ADC
conversion and polling commands. It can also be used
with write commands when all parts are being written with
the same data. Broadcast read commands should not be
used in the parallel configuration.
Address Commands: An address command is one in which
only the addressed device on the bus responds. The first
byte of an address command consists of 4 bits with a
value of 1000 and 4 address bits. Following the address
command is its PEC byte. The third and fourth bytes are
the command byte and its PEC byte respectively. See the
Bus Protocols and Commands section.
Polling Methods: For ADC conversions, three methods can
be used to determine ADC completion. First, a controller
can start an ADC conversion and wait for the specified
conversion time to pass before reading the results. The
second method is to hold CSBI low after an ADC start
command has been sent. The ADC conversion status will
be output on SDO (Figure 5). A problem with the second
method is that the controller is not free to do other serial
communication while waiting for ADC conversions to
complete. The third method overcomes this limitation.
The controller can send an ADC start command, perform
other tasks, and then send a poll ADC converter status
(PLADC) command to determine the status of the ADC
conversions (Figure 6). For OV/UV interrupt status, the poll
interrupt status (PLINT) command can be used to quickly
determine whether any cell in a stack is in an overvoltage
or undervoltage condition (Figure 6).
Table 1. Procedure to Calculate PEC Byte
CLOCK
CYCLE DIN
IN0
IN1
IN2
0
0
0
1
0
1
0
1
1
0
2
0
0
1
1
3
0
0
0
1
4
0
0
0
0
5
0
0
0
0
6
0
0
0
0
7
1
1
1
1
8
PEC[7]
0
1
0
0
0
0
0
0
1
PEC[6]
1
0
0
0
0
0
0
1
1
PEC[5]
0
0
0
0
0
0
1
1
0
PEC[4]
0
0
0
0
0
1
1
0
0
PEC[3]
0
0
0
0
1
1
0
0
0
PEC[2]
0
0
0
1
1
0
0
0
1
PEC[1]
0
1
1
1
0
0
0
0
1
PEC[0]
1
0
1
0
0
0
0
0
1
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