ADBMS1818ASWZ-R7 datasheet(75/89 Pages) AD

75 / 89 page

Data Sheet

ADBMS1818

APPLICATIONS INFORMATION

analog.com

Rev. 0 | 75 of 89

Both circuits are shown in Figure 101. The functionality of the

discharge circuits can be verified by conducting cell measurements

and comparing measurements when the discharge is off to meas-

urements when the discharge is on. The measurement taken when

the discharge is on requires that the discharge permit (DCP) bit

be set. The change in the measurement when the discharge is

turned on is calculable based on the resistor values. The following

algorithm can be used in conjunction with Figure 101 to verify each

discharge circuit:

►

Step 1: Measure all cells with no discharging (all S outputs off)

and read and store the results.

►

Step 2: Turn on S1, S7, and S13.

►

Step 3: Measure C1 to C0, C7 to C6, and C13 to C12.

►

Step 4: Turn off S1, S7, and S13.

►

Step 5: Turn on S2, S8, and S14.

►

Step 6: Measure C2 to C1, C8 to C7, and C14 to C13.

►

Step 7: Turn off S2, S8, and S14.

►

...

►

Step 17: Turn on S6, S12, and S18.

►

Step 18: Measure C6 to C5, C12 to C11, and C18 to C17.

►

Step 19: Turn off S6, S12, and S18.

►

Step 20: Read the Cell Voltage Register Groups to get the

results of Step 2 through Step 19.

►

Step 21: Compare new readings with old readings. Each cell

voltage reading must have decreased by a fixed percentage set

by RDISCHARGE and RFILTER for internal designs and RDISCHARGE1

and RDISCHARGE2 for external MOSFET designs. The exact

amount of the decrease depends on the resistor values and

MOSFET characteristics.

Figure 101. Balancing Self Test Circuit

DIGITAL COMMUNICATIONS

PEC Calculation

The PEC can be used to ensure that the serial data read from the

ADBMS1818 is valid and has not been corrupted. This feature is

critical for reliable communication, particularly in environments of

high noise. The ADBMS1818 requires that a PEC be calculated for

all data being read from and written to the ADBMS1818. For this

reason, it is important to have an efficient method for calculating the

PEC.

The C code provides a simple implementation of a lookup table

derived PEC calculation method. There are two functions. The first

function init_PEC15_Table() must only be called once when the

microcontroller starts and initializes a PEC15 table array called

pec15Table[]. This table is used in all future PEC calculations.

The PEC15 table can also be hard coded into the microcontroller

rather than running the init_PEC15_Table() function at startup. The

pec15() function calculates the PEC and returns the correct 15-bit

PEC for byte arrays of any given length.

/************************************

Permission to freely use, copy, modify, and distribute this software

for any purpose with or without fee is hereby granted, provided

that the above copyright notice and this permission notice appear

in all copies: THIS SOFTWARE IS PROVIDED “AS IS” AND ADI

DISCLAIMS ALL WARRANTIES

INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY

AND FITNESS. IN NO EVENT SHALL ADI BE LIABLE FOR ANY

SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES

OR ANY DAMAGES WHATSOEVER RESULTING FROM ANY

USE OF SAME, INCLUDING ANY LOSS OF USE OR DATA

OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLI-

GENCE OR OTHER TORTUOUS ACTION, ARISING OUT OF OR

IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS

SOFTWARE.

***************************************/

int16 pec15Table[256];

int16 CRC15_POLY = 0x4599;

void init_PEC15_Table()

{

for (int i = 0; i < 256; i++)

{

remainder = i << 7;

for (int bit = 8; bit > 0; --bit)

{

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