Bhagavad Gita · Jnana Vijnana YogaChapter 7, Shloka 1 (7.1)

Shankaracharya — "refuge in me alone". Mayi vakṣyamāṇa-viśeṣaṇe parameśvare āsaktaṃ manaḥ — one whose mind is fixed on the Supreme Lord with the qualities about to be described; mad-āśrayaḥ — an ordinary person, for some human goal, takes refuge in the agnihotra, austerity, charity and the like, ayaṃ tu yogī mām eva āśrayaṃ pratipadyate hitvā anyat sādhanāntaram — but this yogi gives up other means and takes refuge in me alone. Samagraṃ … vibhūti-bala-śakty-aiśvaryādi-guṇa-saṃpannaṃ mām — me "in full", endowed with glory, strength, power, sovereignty and other qualities.

Acharya Ramanuja — separation is unbearable. Mat-priyatvātirekeṇa … viśleṣe sati tat-kṣaṇād eva viśīryamāṇa-svabhāvatayā mayi sugāḍhaṃ baddha-manāḥ — because of intense love for me, one whose mind is deeply bound to me, being of such a nature that it falls apart the moment it is separated from my nature, qualities, divine play (lila) and glory; svayaṃ ca mayā vinā viśīryamāṇatayā mad-āśrayaḥ mad-ekādhāraḥ — and because without me one falls apart, I alone am one's support.

The difference: Shankara — refuge = giving up other means and taking shelter in Ishvara; Ramanuja — love so deep that in separation a person "falls apart" (linking to kṣaṇa-mātra-viyogāsahatā in 6.47).