Hex to binary with all 12 bits

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VB

hi,
i am converting a hex value to its binary equivalent,using the below function
here i am facing one problem,
i am converting a hex value ex.:0A8 it binary equivalent is 10101000
but i want the output as 000010101000.
i want all twelve bits to get displayed.

ex.:050
i want the above value as 000001010000
kindly provide me the solution
the function i have used to convert from hex to binary
Function HexStringToBinary(ByVal hexString As String) As String
Dim num As Integer = Integer.Parse(hexString, Globalization.NumberStyles.HexNumber)
Return Convert.ToString(num, 2)
End Function

as i am counting the number of bits,i need all bits
Thanks in advance

What I have tried:

i am converting a hex value to its binary equivalent,using the below function
here i am facing one problem,
i am converting a hex value ex.:0A8 it binary equivalent is 10101000
but i want the output as 000010101000.
i want all twelve bits to get displayed.

ex.:050
i want the above value as 000001010000
kindly provide me the solution
the function i have used to convert from hex to binary
Function HexStringToBinary(ByVal hexString As String) As String
        Dim num As Integer = Integer.Parse(hexString, Globalization.NumberStyles.HexNumber)
        Return Convert.ToString(num, 2)
    End Function
Thanks in advance