Ragdoll bounces up when apply gravity(due to joint constraint)

Hello, I am new to PhysX. And recently I am working on construct a ragdoll using rigidbodyDynamics and D6Joint. I have setup all the joints. The problem I am facing right now is when apply gravity, the ragdoll falls off, and due to the joint constraints between upper and lower legs, the ragdoll bounces high(which is an unexpected behaviour). and also the rigidbody of it tweak togathor at some point which causes that problem.
I have tried setting the drive like this:
j->setDrive(PxD6Drive::eSLERP, PxD6JointDrive(0, 1000, FLT_MAX, true));
but does not work well. Could u guys give me some advices about how to solve this problem?