I designed BMS(Battery Management System) and used the LTC7001 for charge and discharge FET control.
Application Condition :
1. BAT_OUT : 60 ~ 84V Li-ion Battery
2. B+_LOAD : Motor inverter (Peak DC 100A)
3. CHARGE+ : Li-ion Charger 83V 25A CCCV
4. +12V : Always supplied
5. LOAD_IN : MCU control (3.3V On/Off) - Always turn-on when discharge conditions.
6. CHG_IN : MCU control (3.3V On/Off - Always turn-on when the charger is connected.
7. LOAD FET Part : Total 5ea LTC7001 & OnSemi FDBL0630N150 N-ch MOSFET (Peak Current 20A/1ch)
8. Charge FET Part : Total 2ea LTC7001 & OnSemi FDBL0630N150 N-ch MOSFET (Peak Current 12.5A/1ch)
Test Condition :
1. BAT_OUT : 72V was supplied using power supply.
2. B+_LOAD : No Load
3. CHARGE+ : Not Connected
CHG_IN On / Off was repeated (5s cycle) while 72V was supplied to BAT_OUT and +12V was supplied.
The first few times, 84V is output to Vgate(TGDN and TGUP), so the FET is turned on. However, after this, only 72V is output to Vgate and it does not work.
LOAD_IN on / off works the same. There are much more charging parts than the discharge part.
In some cases, only 12V is output to Vgate or FET dies.
I have replaced over 30 LTC7001 so far and the same thing happens.
I can not really understand. Please help me.
You can't use five controllers in parallel to discharge the battery to the load. The same is true for charging. These controller may not turn ON the FET at the same time and load current may not share equally. See my suggestions below.
1. Use one controller for charging and one controller for discharging.
2. Use one ultra low Rds(ON) FET if possible. If not, use multiple FETs in parallel configuration connected to one controller.
3. Use 0 to 10 ohm, 1206 resistor that is connected to TGUP and FET gate pin. You don't want to slow down the FET turn ON speed.
4. Add multiple Schottky diodes with 10A and 30A rating and place them close to TS pin and GND node.
5. Add multiple TVS (SMDJ90A) at the drain of the power MOSFET.
6. Populate boost diode (diode connected to VCC and BST pins) with MMBD1501A or CMPD3003 diode.
Thank you for your kind reply.
Based on your advice and datasheet, I've configured the following:
1. Is the image correct?
2. "4. Add multiple Schottky diodes with 10A and 30A rating and place them close to TS pin and GND node."
I don't know the Schottky diode connection. Do I configure 30A and 10A to be connected in series?(see diagram) Or do I configure 30A and 10A in parallel?
10A Schottky : SDT10100P5-13 (Diodes)30A Schottky : SDT30B100D1-13 (Diodes)
3. Only one Gate Driver IC (LTC7001) is used, and the FDBL0630N150 FET is planned to connect five in parallel.
Is it possible to turn-on all 5 FETs when configured as shown above?
4. Finally, I would like to hear your valuable opinion about the cause of the problem I asked.
Thanks & Best regards.
I added my recommendations to the image. See below.
I would recommend placing the Schottky diodes in parallel configuration. Place the 10A diode close to the TS pin and GND. Then place 30A diode next to 10A diode since it has bigger size.
For charge FET, use two FETs (FDBL0630N150) in parallel with boost cap of 0.22uF. For load FET, use 6 FETs in parallel (FDBL0200N100) with boost cap of 0.47uF and VCC cap of 4.7uF.
One controller can drive 5 or 6 FETs with appropriately sized boost capacitor.
My educated guest would be that turn off speed of the FET is slow with 220K resistor. This causes failure of the MOSFET.
Thank you for your advice ...
I ordered the part again and received it today.I will inform you of the test result after work.Thank you.
I changed the circuit as you advised:
The following problems occurred during the test.
The gate was turned on with the electronic load set to 5A. Then one of the six FETs burst-out.
1. Gate turn-on to Load 20A is OK
2. Load 5A to Gate turn-on is Failure
I thought the TGUP time was too short to fail. So I added 100K to RG and 22nF / 100V to CG, referring to Figure 5. Powering Large Capacitive Loads in the datasheet.
However, even if the load was set at 0.5A, the output voltage dropped to 42V. (Input power: 72V 10A)
After that the RG value was changed to 4.7kohm, and the voltage dropped in the 2A load even if 10ohm and CG were removed. Especially when CG is present, there is an output voltage drop even at lower current settings. (< 1.5A)
I have to discharge up to 100A. However, there is no problem if the gate turn-on time is less than 1 second because it is not PWM.
I hope to receive your valuable feedback once more. Also, if possible, can you suggest some ways?