I had a hard time finding 1m datasets for LTC so I wrote some code to pull all of it from 2017 until 2018 on the GDAX exchange. I cannot guarantee the accuracy of this data. Use at your own risk.
The format is a SQLite3 database. It should be easy to export to a CSV if necessary. Use 7-zip to extract.
Bitcoin 1m data going back further than 2016 can be downloaded from Kaggle.