Problem with THS1007 ADC four channel configuration.

I have changed the reference supply from external to internal and found
the ADC ( THS1007 ) is working for the below hardware configuration.

The ADC with single channel ( channel 1 ) configured.

The internal reference voltages are enabled and input pulse is fed to
the ADC ( THS1007), through a capacitor for AC
coupling.

The pulse width is about 20uS in 1mS pulse period & The amplitude level
is varied from 40mV to 900mV.

  The ADC input pin is
probed and it is seen that the voltage swing is
from 2.2V to 3.1V. // ( i.e,)
from 2.2V to 2.2V + input voltage swing 0V
to 900mV

When the ADC is tested with four channel configuration, it is observed
that the SYNC pulse output is not as expected as mentioned in the
datasheet and It is observed like those for Two channel configuration, ( i.e,  after
becoming HIGH, it again falls LOW immediate after one clock cycle of CONV CLK).

Following is the configuration followed for testing Four channel
operation.

 1. Written 0x401 ( reset)

  2. Written 0x400 ( reset clear )

  3. Written 0x098 ( Configuration data for 4 channel operation into control register 0 )

 4. Written 0x4B0 ( Configuration data for control register 1, tried with 0x4C0 also )

Kindly clarify the reason for this SYNC pulse behavior even though the
ADC is configured for the 4 channel configuration.