5.1.5. LTC6813-1-based 18-Cell Slave v1.1.3 and above

5.1.5.1. Overview

Important

The following description only applies for the LTC6813-1-based 12 cell BMS-Slave Board hardware versions 1.1.3 to above.

Hint

All connector pinouts described below follow the Convention for Molex Micro-Fit 3.0 Connector Pin Numbering.

5.1.5.2. Specifications

5.1.5.2.1. Electrical Ratings

The current consumption from the module has been measured at 64.8 V module voltage, which is equivalent to a cell voltage of 3.6 V per cell. No sense lines have been connected from this measurement (as the impact of cell voltage sensing is negligible on the current consumption).

The DC supply current has been measured with a voltage of 12 V and no VBAT or cells connected.

Table 5.41 Electrical Ratings

Description	Minimum	Typical	Maximum	Unit
Battery Module Voltage	16	–	90	V
Single Battery Cell Voltage	0	–	5	V
Temperature Sensor Inputs	–	10k	–	\({\Omega}\)
Analog Inputs (pin headers)	0	–	5	V
Digital Inputs/Outputs (pin headers)	0	–	5	V
External DC Supply	8	12	24	V
Current consumption: Primary in sleep, Secondary in sleep	–	13.35	–	\({\mu}A\)
Current consumption: Primary active, Secondary in sleep	–	11.66	–	mA
Current consumption: Primary active, Secondary active	–	22.35	–	mA
DC supply current: Primary in sleep, Secondary in sleep	–	3.3	–	mA
DC supply current: Primary active, Secondary in sleep	–	112.0	–	mA
DC supply current: Primary active, Secondary active	–	211.6	–	mA

5.1.5.2.2. Mechanical Dimensions

Table 5.42 Mechanical Dimensions

Description	Value	Unit
Width	100	mm
Length	160	mm
Height	15	mm
Weight	88	g

5.1.5.2.3. Block Diagram

The block diagram of the BMS-Slave Board is shown in Fig. 5.6

Fig. 5.6 BMS-Slave Board 18-Cell Block Diagram

5.1.5.2.4. Schematic and Board Layout

More information about the board schematic and layout files can be found in section Design Resources.

5.1.5.3. Functions

The following general description applies to both, the primary and the secondary of the BMS-Slave Board. If there are any differences in hardware between the primary and the secondary they will be marked as such.

5.1.5.3.1. Cell Voltage Measurement

The cell voltage sense lines are input on the connector X200. The pinout is described in Table 5.43.

Table 5.43 Cell voltage sense connector

Pin	Signal	Direction	Description
1	VBAT-	Input	Battery module negative terminal
2	CELL_0+	Input	Cell 0 positive terminal
3	CELL_2+	Input	Cell 2 positive terminal
4	CELL_4+	Input	Cell 4 positive terminal
5	CELL_6+	Input	Cell 6 positive terminal
6	CELL_8+	Input	Cell 8 positive terminal
7	CELL_10+	Input	Cell 10 positive terminal
8	CELL_12+	Input	Cell 12 positive terminal
9	CELL_14+	Input	Cell 14 positive terminal
10	CELL_16+	Input	Cell 16 positive terminal
11	VBAT+	Input	Battery module positive terminal
12	not connected	-	-
13	CELL_0-	Input	Cell 0 negative terminal
14	CELL_1+	Input	Cell 1 positive terminal
15	CELL_3+	Input	Cell 3 positive terminal
16	CELL_5+	Input	Cell 5 positive terminal
17	CELL_7+	Input	Cell 7 positive terminal
18	CELL_9+	Input	Cell 9 positive terminal
19	CELL_11+	Input	Cell 11 positive terminal
20	CELL_13+	Input	Cell 13 positive terminal
21	CELL_15+	Input	Cell 15 positive terminal
22	CELL_17+	Input	Cell 17 positive terminal
23	not connected	-	-
24	not connected	-	-

Each of these lines is fused with a fast acting 250 mA surface-mount fuse (F301 - F319) on the board except of the VBAT+ and VBAT- lines which are fused with a value of 500 mA (F300 and F320). This essentially is important for an evaluation environment. The VBAT+ and VBAT- connection is used for the internal power supply of the slave board. If the battery module does not contain these separate wires to the positive and negative module terminal the solder jumpers SJ300 and SJ301 have to be shorted. In this case the slave will be supplied through the sense lines CELL_0- and CELL_11+. Running the slave in this configuration could result in cell measurement errors due to voltage drop on the sense wires.

The cell input lines are filtered by a grounded or differential capacitor filter: both possibilities are provided on the PCB of the BMS-Slave Board. More information on the corner frequency of this filtering can be found in the schematic. The grounded capacitor filter should be used in environments affected with a high noise as it offers a high level of battery voltage ripple rejection. The differential capacitor filter can be used when noise is less frequent or the design is subjected to cost optimization.

5.1.5.3.2. Passive Cell Balancing

The passive balancing circuit is realized by a parallel connection of two 130 \({\Omega}\) discharge-resistors that can be connected to each single cell in parallel. The MOSFET switches (T1500 - T1517) that control the connection to the cells are controlled by the primary LTC6813-1 monitoring IC. The LTC6813-1 on the secondary unit does not support balancing. The resistor value of 2x 130 \({\Omega}\) results in a balancing current of about 55 mA at a cell voltage of 3.6 V. This current results in a power dissipation of about 0.2W per balancing channel (at 3.6 V).

5.1.5.3.3. Global Cell Balancing Feedback

In order to check the proper function of the balancing process or to detect a malfunction in the balancing control circuit, a global balancing feedback signal is connected to the LTC6813-1. This allows the system to check whether any balancing action is currently taking place at any time. The feedback signal is connected to the GPIO3 of the LTC6813-1. The signal remains in a logic zero state until any balancing action on any cell starts.

5.1.5.3.4. Temperature Sensor Measurement

The cell temperature sensors are connected to the connectors X201 (primary) and X202 (secondary). The pinout is identical for the primary and secondary unit and is described in Table 5.44.

Table 5.44 Temperature sensor connector

Pin	Signal	Direction	Description
1	T-SENSOR_0	Input	NTC Sensor 0 terminal 1
2	T-SENSOR_1	Input	NTC Sensor 1 terminal 1
3	T-SENSOR_2	Input	NTC Sensor 2 terminal 1
4	T-SENSOR_3	Input	NTC Sensor 3 terminal 1
5	T-SENSOR_4	Input	NTC Sensor 4 terminal 1
6	T-SENSOR_5	Input	NTC Sensor 5 terminal 1
7	T-SENSOR_6	Input	NTC Sensor 6 terminal 1
8	T-SENSOR_7	Input	NTC Sensor 7 terminal 1
9	FUSED_VBAT-	Input	NTC Sensor 0 terminal 2
10	FUSED_VBAT-	Input	NTC Sensor 1 terminal 2
11	FUSED_VBAT-	Input	NTC Sensor 2 terminal 2
12	FUSED_VBAT-	Input	NTC Sensor 3 terminal 2
13	FUSED_VBAT-	Input	NTC Sensor 4 terminal 2
14	FUSED_VBAT-	Input	NTC Sensor 5 terminal 2
15	FUSED_VBAT-	Input	NTC Sensor 6 terminal 2
16	FUSED_VBAT-	Input	NTC Sensor 7 terminal 2

Standard 10 \({k\Omega}\) NTC resistors are recommended for use. When using other values than these, the series resistors (R100-R107) on the board may have to be adjusted. Please note that the accuracy of the internal voltage reference VREF2 decreases heavily with a load of over 3 mA. Using 8x 10 \({k\Omega}\) NTC resistors with the corresponding 10 \({k\Omega}\) series resistors results in a current of 1.2mA (at 20 °C) which is drawn from VREF2.

Each 8 temperature sensors are connected to an analog multiplexer. The analog multiplexer can be controlled via I²C by the LTC6813-1 (7-bit address: 0x4C). In order to ensure fast settling times after switching the multiplexer input, the output signal of the multiplexer is buffered by an operational amplifier. Finally the analog voltage of the selected sensor is measured on the GPIO1 pin of the LTC6813-1.

5.1.5.3.5. On-board EEPROM

The primary unit as well as the secondary unit of the foxBMS BMS-Slave board is equipped with an EEPROM IC (IC801). The EEPROM for example can be used for storing data such as calibration values. Similar to the analog multiplexers, the EEPROM device is connected to the I²C bus of the LTC6813-1 (7-bit address: 0x50).

5.1.5.3.6. On-board Ambient Temperature Sensor

For an additional monitoring of the ambient temperature an on-board temperature sensor is used. This temperature sensor can be read by the LTC6813-1 via the I²C bus (7-bit address: 0x48). It is possible to program an alert temperature. Once the measured temperature reaches this alert temperature the alert pin of the IC is set to a logic low level. Currently this signal is not used on the BMS-Slave board, but it is accessible on the connector X404.

5.1.5.3.7. Additional Inputs and Outputs

Several additional analog and digital inputs and outputs are provided on the BMS-Slave board via pin headers. Each 16 analog inputs are provided on connector X400 (primary) and X401 (secondary). The pinout for the connectors for the primary and secondary unit is identical and is described in Table 5.45.

Table 5.45 Connector for analog inputs

Pin	Signal	Direction	Description
1	ANALOG-IN_0	Input	Analog input 0
2	ANALOG-IN_1	Input	Analog input 1
3	ANALOG-IN_2	Input	Analog input 2
4	ANALOG-IN_3	Input	Analog input 3
5	ANALOG-IN_4	Input	Analog input 4
6	ANALOG-IN_5	Input	Analog input 5
7	ANALOG-IN_6	Input	Analog input 6
8	ANALOG-IN_7	Input	Analog input 7
9	ANALOG-IN_8	Input	Analog input 8
10	ANALOG-IN_9	Input	Analog input 9
11	ANALOG-IN_10	Input	Analog input 10
12	ANALOG-IN_11	Input	Analog input 11
13	ANALOG-IN_12	Input	Analog input 12
14	ANALOG-IN_13	Input	Analog input 13
15	ANALOG-IN_14	Input	Analog input 14
16	ANALOG-IN_15	Input	Analog input 15
17	+3.0V_VREF2	Output	LTC6813-1 3.0V voltage reference
18	FUSED_VBAT-	Output	GND

Each 8 analog inputs are connected to an analog multiplexer. The analog multiplexers can be controlled via I²C by the LTC6813-1 (7-bit addresses: 0x4D and 0x4E). In order to ensure fast settling times after switching the multiplexer input, the output signals of the multiplexers are buffered by operational amplifiers. Finally the analog voltage of the selected sensor can be measured on the GPIO2 pin of the LTC6813-1.

Each 8 digital inputs/outputs are provided on the connectors X402 (primary) and X403 (secondary). The pinout for the connectors for the primary and secondary unit is identical and is described in Table 5.46.

Table 5.46 Connector for digital IOs

Pin	Signal	Direction	Description
1	DIGITAL-IO_0	Input/Output	Digital input/output 0
2	DIGITAL-IO_1	Input/Output	Digital input/output 1
3	DIGITAL-IO_2	Input/Output	Digital input/output 2
4	DIGITAL-IO_3	Input/Output	Digital input/output 3
5	DIGITAL-IO_4	Input/Output	Digital input/output 4
6	DIGITAL-IO_5	Input/Output	Digital input/output 5
7	DIGITAL-IO_6	Input/Output	Digital input/output 6
8	+5.0V_VREG	Output	LTC6813-1 5.0V regulated voltage
9	FUSED_VBAT-	Output	GND

Each 8 digital inputs/outputs are connected to an I²C controlled port expander (7-bit address: 0x20). The direction of the inputs/outputs as well as the logic levels on the pins can be selected by register settings. Each of the 8 digital inputs/outputs has a discrete pull up resistor that for example can be used for directly connecting a tactile switch.

5.1.5.3.8. isoSPI Daisy Chain Connection

The data transmission between the slaves and between the slaves and the basic board takes place using the isoSPI interface. The isoSPI signals are input/output on the connectors X500/X501 (primary) and X502/X503 (secondary). The isoSPI ports are bidirectional, that means they can be used in forward and reverse direction. The isoSPI connections are isolated galvanically using pulse transformers (TR1400). The voltage amplitude of the differential signal can be adjusted by setting resistors (see paragraph Daisy Chain Communication Current).

The pinout of the isoSPI connectors is described in Table 5.47 and Table 5.48.

Table 5.47 isoSPI Daisy Chain Input Connectors

Pin	Daisy Chain
1	IN+ (Primary/Secondary LTC6813-1)
2	IN- (Primary/Secondary LTC6813-1)

Table 5.48 isoSPI Daisy Chain Output Connectors

Pin	Daisy Chain
1	OUT+ (Primary/Secondary LTC6813-1)
2	OUT- (Primary/Secondary LTC6813-1)

5.1.5.3.9. Hardware Settings / Options

5.1.5.3.9.1. Software Timer

The internal software timer of the LTC6813-1 can be enabled/disabled by a dedicated external pin (SWTEN, pin 36 of the LTC6813-1). In order to support all features, the foxBMS BMS-Slave board offers a possibility to switch the software timer. The software timer is enabled in the standard configuration, which means pin 36 is pulled to VREG via a zero-ohm resistor (R1407). The timer can be disabled by removing the resistor R1407 and placing a zero-ohm resistor to R1406.

5.1.5.3.9.2. Daisy Chain Communication Current

The daisy chain communication current can be set by the resistors R1400 and R1402. The default value is 820 \({\Omega}\) for R1402 and 1.2 \({k\Omega}\) for R1400. This values result in a bias current of approximately 1mA and a differential signal amplitude of 1.18 V. Theses values are suitable for high noise environments with cable lengths of over 50m. More information can be found in the LTC6813-1 data sheet.

5.1.5.3.9.3. Status LED

The status LEDs LD1400 show the current mode of each, the primary and secondary LTC6813-1. The LED is on in STANDBY, REFUP or MEASURE mode, whereas the LED is off in SLEEP mode. The LED can be disabled by removing the resistor R1403 next to the LED.

5.1.5.3.9.4. GPIO Extension Connector

The internal GPIO lines 1 to 5 of the primary or secondary LTC6813-1 can be connected to the GPIO extension pin header X404 via optional zero-ohm resistors. In the standard configuration these resistors are not placed. Of course it is possible to place each both resistors for a parallel connection of the internal signals to the GPIO extension connector. For more information see the corresponding page of the schematics. The placement of the resistors and the resulting connection is shown in Table 5.49.

Table 5.49 GPIO extension connector

GPIO	connect to pin header	connect to internal function
1	R1408	R1409 (default)
2	R1410	R1411 (default)
3	R1412	R1413 (default)
4	R1414	R1415 (default)
5	R1416	R1417 (default)

The pinout of the extension connector X404 is described in Table 5.50.

Table 5.50 Extension connector

Pin	Signal	Direction	Description
1	+3.0V_VREF2_0	Output	Primary LTC6813-1 3.0V reference voltage 2
2	+3.0V_VREF2_1	Output	Secondary LTC6813-1 3.0V reference voltage 2
3	+5.0V_VREG_0	Output	Primary LTC6813-1 5.0V regulated voltage
4	+5.0V_VREG_1	Output	Secondary LTC6813-1 5.0V regulated voltage
5	PRIMARY-GPIO1-OPT	Input/Output	Primary LTC6813-1 GPIO1
6	SECONDARY-GPIO1-OPT	Input/Output	Secondary LTC6813-1 GPIO1
7	PRIMARY-GPIO2-OPT	Input/Output	Primary LTC6813-1 GPIO2
8	SECONDARY-GPIO2-OPT	Input/Output	Secondary LTC6813-1 GPIO2
9	PRIMARY-GPIO3-OPT	Input/Output	Primary LTC6813-1 GPIO3
10	SECONDARY-GPIO3-OPT	Input/Output	Secondary LTC6813-1 GPIO3
11	PRIMARY-GPIO4-OPT	Input/Output	Primary LTC6813-1 GPIO4
12	SECONDARY-GPIO4-OPT	Input/Output	Secondary LTC6813-1 GPIO4
13	PRIMARY-GPIO5-OPT	Input/Output	Primary LTC6813-1 GPIO5
14	SECONDARY-GPIO5-OPT	Input/Output	Secondary LTC6813-1 GPIO5
15	PRIMARY-WDT	Output	Primary LTC6813-1 watchdog output
16	SECONDARY-WDT	Output	Secondary LTC6813-1 watchdog output
17	PRIMARY-TEMP-ALERT	Output	Primary board temp. sensor alarm output
18	SECONDARY-TEMP-ALERT	Output	Secondary board temp. sensor alarm output
19	FUSED_VBAT-	Output	GND
20	FUSED_VBAT-	Output	GND

The GPIO lines 6 to 9 are wired to the connector X405 permanently. There is no internal function for this GPIO lines. The pinout of the extension connector X405 is described in Table 5.51.

Table 5.51 Additional GPIO extension connector

Pin	Signal	Direction	Description
1	PRIMARY-GPIO6	Input/Output	Primary LTC6813-1 GPIO6
2	SECONDARY-GPIO6	Input/Output	Secondary LTC6813-1 GPIO6
3	PRIMARY-GPIO7	Input/Output	Primary LTC6813-1 GPIO7
4	SECONDARY-GPIO7	Input/Output	Secondary LTC6813-1 GPIO7
5	PRIMARY-GPIO8	Input/Output	Primary LTC6813-1 GPIO8
6	SECONDARY-GPIO8	Input/Output	Secondary LTC6813-1 GPIO8
7	PRIMARY-GPIO9	Input/Output	Primary LTC6813-1 GPIO9
8	SECONDARY-GPIO9	Input/Output	Secondary LTC6813-1 GPIO9

5.1.5.3.10. External Isolated DC- Supply

It is possible to supply the BMS-Slave Board by an external DC power supply with a voltage range of 8 V to 24 V. The DC input is protected against reverse voltage and over-current (with a 1.25 A fuse). The external DC supply has to be connected on connector X1001 or X1002 (both connectors are in parallel for daisy chaining the supply). The pinout of the connectors X1001 and X1002 is shown in Table 5.52.

Table 5.52 External DC supply connector

Pin	Signal	Direction	Description
1	DC+	Input	positive supply terminal
2	DC-	Input	negative supply terminal