XML 18 R1.htm IDEA: XBRL DOCUMENT v3.21.1
Cover Page - USD ($)
$ in Billions
 12 Months Ended
Mar. 26, 2021
May 10, 2021
Cover [Abstract]    
Document Type 10-K  
Document Annual Report true  
Document Period End Date Mar. 26, 2021  
Current Fiscal Year End Date --03-26  
Document Transition Report false  
Entity File Number 001-39675  
Entity Registrant Name ALLEGRO MICROSYSTEMS, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 46-2405937  
Entity Address, Address Line One 955 Perimeter Road  
Entity Address, City or Town Manchester,  
Entity Address, State or Province NH  
Entity Address, Postal Zip Code 03103  
City Area Code 603  
Local Phone Number 626-2300  
Title of 12(b) Security Common Stock, par value $0.01 per share  
Trading Symbol ALGM  
Security Exchange Name NASDAQ  
Entity Well-known Seasoned Issuer No  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
ICFR Auditor Attestation Flag false  
Entity Shell Company false  
Entity Public Float   $ 1.3
Entity Common Stock, Shares Outstanding (in shares)   189,593,243
Documents Incorporated by Reference Portions of the registrant’s proxy statement for its 2021 Annual Meeting of Stockholders to be filed pursuant to Regulation 14A within 120 days of the end of the registrant’s fiscal year ended March 26, 2021 are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.  
Entity Central Index Key 0000866291  
Amendment Flag false  
Document Fiscal Year Focus 2021  
Document Fiscal Period Focus FY