How to set number of characters in input field ?

I am creating an input field dynamically (via CL_WD_INPUT_FIELD).

I am binding the value (via BIND_VALUE) to an attribute with type CHAR30.

I want to give the possibility to enter a number with 4 digits (0 - 9999).

Is it possible to restrict the number of characters that can be entered to 4 (although the BIND_VALUE attribute has a type CHAR30, that allows 30)?

I have tried it via set_length, bind_length but it seems that the length of the BIND_VALUE attribute overrules the length information...