Correct Wiring for FRDM-MC33771BTPL EVB with 14-Cell Battery Pack – Balancing and ISENSE Questions

[AbdullahMohamed]

I’m working on a Battery Management System (BMS) graduation project using NXP tools:
- Master: KL25Z
- Transceiver: FRDM-MC33664EVB
- Slave: FRDM-MC33771BTPL EVB (connected to battery cells).

### Current Setup:
1. Battery Pack: 14 Li-ion cells in series (as shown in the attached image).
2. Wiring to Slave Pins:
- Positive terminal of the entire pack (Cell 1+) → Split into 4 wires → Connected to pins 1, 2, 3 (and pin 4 left open).
- Intermediate connections:
- Cell 1- (Cell 2+) → Pin 5
- Cell 2- (Cell 3+) → Pin 7
- ... (continuing sequentially).
- CB Pins: Left unconnected (no external balancing resistors).
- ISENSE Pins: Currently floating (unsure how to wire the shunt resistor shown in the image).

### Questions:
1. Wiring Validation: 
- Is this wiring correct, or could it risk damaging the board?
- The datasheet implies CB pins are only needed with external balancing resistors. Since I’m using the MC33771B’s internal balancing, can I leave CB pins disconnected?

2. ISENSE Resistor:
- The attached image shows a 100A/75mV shunt resistor (127g, 104, 7.7).
- How should I wire this to the ISENSE+/- pins? Is this resistor suitable for current sensing?

3. Jumper Wires: 
- I’m using 22 AWG jumper wires (rated 1A). Given the battery pack’s potential current, could this be a hazard? Should I use thicker wires (e.g., 16 AWG)?

4. General Advice:
- Any critical dos/don’ts when connecting the battery pack directly (without an emulator)?

 

 

Attachments:
- Image of battery pack wiring.
- Shunt resistor specs.

[JozefKozon]

Dear Abdallah,

please consider to sign for NDA (Non-Disclosure Agreement) with NXP. Then you would be able to download the confidential documents. To sign a new NDA with NXP please create a new case here and an NXP representative for NDA matters will help you with the process.

### Current Setup:
1. Battery Pack: 14 Li-ion cells in series (as shown in the attached image).
2. Wiring to Slave Pins:
- Positive terminal of the entire pack (Cell 1+) → Split into 4 wires → Connected to pins 1, 2, 3 (and pin 4 left open).
- Intermediate connections:
- Cell 1- (Cell 2+) → Pin 5
- Cell 2- (Cell 3+) → Pin 7
- ... (continuing sequentially).
- CB Pins: Left unconnected (no external balancing resistors).
- ISENSE Pins: Currently floating (unsure how to wire the shunt resistor shown in the image).

[A] If you have 14 Cells, then all pins should be connected to the battery pack. Please download and refer to the FRDM33771BTPLEVB schematic. You can download the schematic from the FRDM33771BTPLEVB product page, under the Design Files->Secure section. 

There you can also find the shunt resistor connection. Please note, you need to have signed NDA with NXP and you need to be registered on the nxp.com to be able to download any confidential file, including the design files. 

### Questions:
1. Wiring Validation: 
- Is this wiring correct, or could it risk damaging the board?
- The datasheet implies CB pins are only needed with external balancing resistors. Since I’m using the MC33771B’s internal balancing, can I leave CB pins disconnected?

2. ISENSE Resistor:
- The attached image shows a 100A/75mV shunt resistor (127g, 104, 7.7).
- How should I wire this to the ISENSE+/- pins? Is this resistor suitable for current sensing?

[A1/2] If you have 14 Cells, all the CB pins and CT pins must be connected. Each Cell is controlled individually by the MC33771B. Please refer to the FRDM33771BTPLEVB schematic and/or to the MC33771B full datasheet. Shunt resistor connection is also described in there. Full datasheet is available in the MC33771B product page, under the Documentation->Secure section. 

3. Jumper Wires: 
- I’m using 22 AWG jumper wires (rated 1A). Given the battery pack’s potential current, could this be a hazard? Should I use thicker wires (e.g., 16 AWG)?

[A] Maximum allowed balancing current for the MC33771B is 300mA per channel/Cell. The FRDM33771BTPLEVB is designed, not to exceed this current. If you haven't made any modification to the board, there will never be higher current, than 300mA per channel/Cell. The 1A wires are sufficient for this board.

4. General Advice:
- Any critical dos/don’ts when connecting the battery pack directly (without an emulator)?

[A] Please download the refer to the FRDM33771BTPLEVB schematic for the Cells in the battery pack connection. 

With Best Regards,

Jozef

[AbdullahMohamed]

Thank you for your response, Jozef, but I regret to inform you that I have tried repeatedly to sign the NDA and have been unable to obtain it because I am a university student and I need the information for my graduation project to be able to run the project. The NDA requires company information and does not accept the university. What should I do? I contacted support, customer service, and sent emails, but I have not reached any results.

Tell me what to do.

[JozefKozon]

Dear Abdallah,

I understand your situation, but unfortunately I/we in NXP cannot share confidential information without signed NDA. From previous cases, Universities can sign NDA with NXP, but your University must be willing to sign it and then follow the NDA rules. If your University do not want to sign the NDA, you can have only the public information. 

I apologize for inconvenience. 

With Best Regards,

Jozef

[AbdullahMohamed]

Do the ISENSE pins of the MC33771B need to be connected, or can they be left unconnected?

[JozefKozon]

Dear Abdallah,

if you don't want to use the ISENSE pins, please connect them to the GND.

If you want to use the ISENSE pins, then a shunt and external circuitry need to be used as described in the section 13.2.4 in the MC33771 datasheet. 

With Best Regards,

Jozef

[AbdullahMohamed]

Thank you very much