The reference design is categorized into five sections to explain the design in terms of the application:

• DCDC power
• Cell monitor, NTC, and digital isolator
• Connectors
• Daisy chain
• Wireless

Figure 3-1 TIDA-020076 Schematic: DCDC Power

Two methods can power the BQ79718B-Q1: DCDC power and LDO power. This reference design includes both methods, but only one method can be selected. DCDC power provides more efficiency and LDO power has lower cost.

DCDC power is needed when the customer requires lower current consumption.

Figure 3-2 TIDA-020076 Schematic: Cell Monitor

For the main cell monitor design, an LDO power on the top right corner is needed when the DCDC power is not populated.

On the top left corner, these components provide the design for sensing the NTC outside and on the board. RT1 is the NTC on the board and RT2 is PTC on the board. Select one of these components.

S1, S2, S3, and S4 are the switches to select the function needed. To test NTC outside, put S1 PIN1, PIN2, PIN3, PIN4, and PIN5 on. Put S1 PIN6 on to test the NTC value on the board.

GPIO0 and RX default to UART RX at reset until I2C is enabled. When unused (for example, for stack devices), short RX to AVDD or use with pullup resistor less than 20kΩ (turn S3 PIN 1 on). When used as UART RX, pull up to AVDD with larger than 70kΩ (turn off S1 PIN1).

AVDD remains on during SHUTDOWN mode when a large resistor (greater than 70kΩ) is connected between GPIO0 and RX and AVDD. AVDD allows an external device such as wireless RX and TX to be powered in SHUTDOWN.

AVDD turns off when the device is in SHUTDOWN mode when GPIO0 pullup resistor is less than 20kΩ.

To test wireless, the power supply for WBMS LDO is LDOIN or WL_PWR. Turn S4 PIN1 or keep R8 populated.

J25 is not needed to perform any test or measurement outside. The caps from GPIO to GND are needed for ESD protection.

In the middle of this page, D1 and D12 are the LEDs for FAULT and DVDD. D7 and D8 are needed when the customer requires more strict EMC test conditions.

On the bottom left, U7 is the digital isolator when there is a need for isolated UART communication requirement. J3 and J7 are the output connectors for these isolated signals.

Figure 3-3 TIDA-020076 Schematic: Connectors

On the left of the connector page, this section shows the design of the BB pin. The BB pin is used to bypass or to sense the voltage of the bus bar. When the BB pin is used, populate only 1 pair of capacitors; otherwise, keep all the capacitors and resistances unpopulated.

The balance resistance value in CB RC string is decided by the balance current requirement and the VC RC string can be adjusted based on the EMC test result. D9, D10, D4, D5, D6, and D13 need to be populated when the EMC test cannot pass.

The 0Ω resistances between each channel, VBATP and GND are only populated when the channels are not used. Change the 0Ω resistances to 10kΩ, then 0Ω can be used as the resistor ladder to divide the input voltage to each channel.

J9 and J11 are used as the input voltage connector when the 0Ω resistances are changed to 10kΩ resistor ladder.

Figure 3-4 TIDA-020076 Schematic: Daisy Chain

Two different daisy chain setups exist: transformer isolation and capacitor isolation. Select different populated devices to select different isolation types.

Figure 3-5 TIDA-020076 Schematic: Wireless

The core device of the wireless part is CC2662. The power supply of this device is 3.3V, so a 3.3V LDO is needed. Also, a 5V to 3.3V level shifter is needed for the UART communication. The watchdog is used for functional safety requirements. JTAG connector J1 is used to download the software to CC2662.

J4 and J6 are used only when performing the measurement. J2 is used to measure the wireless signal.