ltc4015 battery charger does not charge

This is the first product based on LTC4015 in our teamand now we meet a trouble. Please give some valuable advice to us.

 System information:

Vin 18V 0.5A

Battery 2S, Voltage is 8V

No load and MAIN_LINE_P is NC

 Problem:

  1. The LTC4015 does not charge batteries;
  2. I2C read register OK, but no Vin no telemetry data.

SYSTEM_STATUS is 0x2AC70010 1010 1100 0111

CHEM_CELLS is 0x22

CHARGER_STATE is 0x40

CHARGE_STATUS is 0

SCHEMATIC:

SW pin wave form:

TG pin wave form:

BG pin wave form: