Prueba con esto...
Data:
l_scal_week LIKE scal-week,
l_date_low like sy-datum,
l_date_high like sy-datum.
* Semana para una fecha
CALL FUNCTION 'DATE_GET_WEEK'
EXPORTING
date = sy-datum
IMPORTING
week = l_scal_week
EXCEPTIONS
date_invalid = 1
OTHERS = 2.
IF sy-subrc <> 0.
EXIT.
ENDIF.
* Primer Dia de la Semana
CALL FUNCTION 'WEEK_GET_FIRST_DAY'
EXPORTING
week = l_scal_week
IMPORTING
date = l_date_low
EXCEPTIONS
week_invalid = 1
OTHERS = 2.
IF sy-subrc <> 0.
EXIT.
ENDIF.