MAX11068 datasheet(21/82 Pages) MAXIM

21 / 82 page

12-Channel, High-Voltage Sensor, Smart

Data-Acquisition Interface

For every module in the battery pack, a 1Fs communi-

cation delay is incurred while the scan command is for-

warded up the SMBus ladder. Therefore, the difference

in the scan completion time from the first module to the

last module in a chain is no more than 1Fs x (no. of mod-

ules in the chain - 1) as shown in Figure 11.

Taking the module conversion time and combining it with

the communication delay, the overall sampling window

of the system can be calculated:

Sampling window = 11.3Fs + (5.67Fs + (no. of cells

enabled per module -1) x 3.83Fs) x 2 phases + ((no. of

modules per pack - 1) x 1Fs per module)

So, for a battery pack that uses 12 cells per module and

a system with four modules (total cell count = 48), the

sampling window would be:

Sampling Window = 11.3 + (5.67 + 11 x 3.83Fs) x 2 +

((4 Modules -1) x 1Fs)

Sampling Window = (106.9Fs) + (3Fs) = 109.9Fs

Thus, from the time the first device receives the scan

command until the last device completes its measure-

ment conversion, 109.9Fs elapse.

The final aspect of the measurement conversion is the

retrieval of data from all devices. A READALL command

is the only way to transfer data from each device. Since

up to 12 cells are measured, the READALL command

must be performed for each cell whose data must be

transferred. For each READALL command, there are 5

total bytes of overhead. These include the broadcast

address byte, the command code byte (register address

to be read), the I2C address byte, the data check byte,

and the packet-error check (PEC) byte. Each of these

bytes has an acknowledge bit associated with it. The

plus 2 acknowledge bits. Finally, the overall data stream

consists of 3 more bits, start, stop, and repeated start.

Thus, for a read of a single register from all modules, the

total bit count is:

READALL bit count = 3 + 5 x 8 + 5 + no. of modules x

(2 x 8 + 2) = 120

Figure 11. Measurement Scan Timing for a Multimodule System

SCAN AT t0

COMMAND FORWARDING

DELAY = 1µs

MODULE N

tALL MODULES = (NO. OF MODULES X 1µs) + 107µs

MODULE 5

tALL MODULES

MODULE 1

MODULE 2

MODULE 3

MODULE 4

MAX11068

Maxim Integrated

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