LTC6804-1 Datasheet, PDF(65/72 Page) Linear Technology

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LTC6804-1 Datasheet, PDF (65/72 Pages) Linear Technology – Multicell Battery Monitors

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LTC6804-1/LTC6804-2

APPLICATIONS INFORMATION

USING THE LTC6804 WITH LESS THAN 12 CELLS

If the LTC6804 is powered by the battery stack, the

minimum number of cells that can be monitored by the

LTC6804 is governed by the supply voltage requirements

of the LTC6804. The sum of the cell voltages must be at

least 11V to properly bias the LTC6804. Figure 40 shows

an example of the LTC6804 when used to monitor eight

cells with best cell measurement synchronization. The 12

cells monitored by the LTC6804 are split into two groups

of 6 cells and are measured using two internal multiplexers

and two ADCs. To optimize measurement synchronization

in applications with less than 12 Cells the unused C pins

should be equally distributed between the top of the second

NEXT HIGHER GROUP

OF 8 CELLS

V+

LTC6804

C12

S12

C11

S11

C10

S10

mux (C12) and the top of the first mux (C6). If there are an

odd number of cells being used, the top mux should have

fewer cells connected. The unused cell channels should

be tied to the other unused channels on the same mux

and then connected to the battery stack through a 100Î©

resistor. The unused inputs will result in a reading of 0V

for those cells channels. It is also acceptable to connect

in the conventional sequence with all unused cell inputs

at the top.

CONNECTING MULTIPLE LTC6804-1 ON THE SAME PCB

When connecting multiple LTC6804-1 devices on the

same PCB, only a single transformer is required between

the LTC6804â1 isoSPI ports. With multiple LTC6804-1

devices on the same PCB, the noise rejection requirements

are significantly lower and the isolation requirements are

simplified. For this reason, a single transformer should be

adequate to provide the required isolation and noise rejec-

tion between ICs on the battery stack. Figure 41 shows an

example application that has multiple LTC6804-1s on the

same PCB, communicating to the bottom MCU through

a LTC6820.

CONNECTING A MCU TO AN LTC6804-1 WITH AN

isoSPI DATA LINK

A separate device, the LTC6820, will convert standard

4-wire SPI into a 2-wire isoSPI link that can communi-

cate directly with the LTC6804. An example is shown in

Figure 42. The LTC6820 can be used in applications to

easily provide isolation between the controller and the

stack of LTC6804s. The LTC6820 also enables system

configurations that have the BMS controller at a remote

location relative to the LTC6804 ICs and the battery pack.

CONFIGURING THE LTC6804-2 IN A MULTI-DROP

isoSPI LINK

Vâ

NEXT LOWER GROUP

OF 8 CELLS

680412 F40

Figure 40. 8 Cell Connection Scheme

The addressing feature of the LTC6804-2 allows multiple

devices to be connected to a single isoSPI master by

multi-dropping them along one twisted pair essentially

creating a large parallel SPI network. An example multi-

drop system is shown in Figure 43 , the twisted pair

should be terminated only at the beginning (master) and

680412f

For more information www.linear.com/LTC6804-1

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