How to set TC275 into sleep mode

How to set TC275 into sleep mode ?

I do this :

IfxCpu_setCoreMode(&MODULE_CPU0, IfxCpu_CoreMode_sleep);
IfxCpu_setCoreMode(&MODULE_CPU1, IfxCpu_CoreMode_sleep);
IfxCpu_setCoreMode(&MODULE_CPU2, IfxCpu_CoreMode_sleep);

but it can't into sleep mode successful , I need to do anything else?
How to set TC275 into sleep mode successfully ?
Does anyone know?