How to transfer with the help of php to MS SQL prepared statement variables indicating the type and their length?

Question

PHP

I am using PDO for the sqlsrv driver. The mssql profiler shows that all queries come to the database with varchar variables, which means that the database has to do an implicit conversion.
It seems that sqlsrv has constants that allow you to specify the type of a variable, but as far as I understand, these constants do not work with PDO.
Are there options other than to drop pdo?