def _int_to_bin_str(value):
    """
    This function returns the integer value in binary string of length 16.
    :param value: integer value to be converted to binary string.
    :return: None if 0 > value > 2^16-1
    """
    if 0 < value < (2**16):
        bits = bin(value)[2:]
        return ('0'*16)[len(bits):] + bits
    else:
        None