freeradius chap auth with ldap

How freeradius does chap auth using ldap server ? In pap, it binds with user's clear password to ldap server, and ldap server sends success bind if pawword is true. When using chap, how it can bind to ldap server? Does it send chap password to the ldap server? Is it needed another software with freeradius+ldap server(for example 389 DS) for doing chap authentication?