Código HTML:
$shhd = mysql_query("SELECT SEC_TO_TIME(SUM(TIME_TO_SEC(horas_des))) AS hoursd FROM gclaudia WHERE fecha BETWEEN '$desde' AND '$hasta'");
Código PHP:
while($productos2 = mysql_fetch_array($shhd))
$hora = date(" H",$productos2['hoursd']());
$min= date(" i",$productos2['hoursd']());
$min_dec = ($min * 100) / 60 ;
$pdf->Cell(25,8,$hora.','.$min_dec,0);