How cryptographic hardware accelerator is secure?

I am using cryptographic hardware accelerator of am335x. As per documentation it unloads the cryptographic operations from the main CPU and hence increases the performance. But from the security point of view how is it useful. In the documentation of 'self encrypted disks'(SED) it is given that the encryption key can not be accessed outside the dedicated processing chip. Hence any malware can not access the keys from RAM. Is it true in the case of am335x? Or are those keys stored in RAM?