i need var in where

I am getting a variable in php , but I can not use it to define where.

include( "../extensions/Editor-1.3.3/php/DataTables.php" );

$var2=$_POST['ID_CAMPO'];

use
    DataTables\Editor,
    DataTables\Editor\Field,
    DataTables\Editor\Format,
    DataTables\Editor\Join,
    DataTables\Editor\Validate;

$editor = Editor::inst( $db, 'ING_VALOR_CAMPO' )
    ->pkey('ID')
    ->fields(           
        field::inst( 'ID'),
        Field::inst( 'ID_CAMPO'),
        Field::inst( 'ID_ASEGURADORA'),
        Field::inst( 'VAL_CAMPO') ->validator('Validate::required'),
        Field::inst( 'DESC_VALOR') ->validator('Validate::required'),
        Field::inst( 'SECUENCIA') ->validator('Validate::required')     
             )
    ->where( 'ID_CAMPO', $var2 )       
    ->process($_POST)
    ->json();