function getStartAndEndDate($week, $year) {
$dto = new DateTime();
$dto->setISODate($year, $week);
$ret['week_start'] = $dto->format('Y-m-d');
$dto->modify('+6 days');
$ret['week_end'] = $dto->format('Y-m-d');
return $ret;
}
$week_array = getStartAndEndDate(1,2020);
print_r($week_array);