LTC7001 Bootstrapped Error

Hi. everyone.

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

Issue :

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.