From their website:
How often can I request samples from TI?
TI accepts a limited number of sample requests from each user. The maximum number of requests varies by user and depends upon what type of TI customer you are.
You can enter additional requests. If you are over the limit, TI will hold your request for review. TI may accept or reject escalated requests. You will receive an email notice of the decision. Accepted requests are processed as normal. Rejected requests are not processed and you will receive a rejection confirmation email message.
Regardless of your TI customer type, you will need to validate your email address with us by following the instructions in an email you receive after creating a myTI profile. If your sample request or access is denied, it may be that you have not validated your email address or TI has associated your account with some type of abusive behavior.