Maybe this article will be useful: Detachment and Compassion in Early Buddhism
Viraaga literally means the absence of raaga: the absence of lust, desire, and craving for existence. Hence, it denotes indifference or non-attachment to the usual objects of raaga, such as material goods or sense pleasures. Non-attachment is an important term here if the Pali is to be meaningful to speakers of English. It is far more appropriate than "detachment" because of the negative connotations "detachment" possesses in English.
The word which Thanissaro Bhikkhu translated as "dispassion", e.g. starting this sutta, is virāgā.
In fact, at least three strands of meaning in the term "compassion" can be detected in the texts: a prerequisite for a just and harmonious society; an essential attitude for progress along the path towards wisdom; and the liberative action within society of those who have become enlightened or who are sincerely following the path towards it. All these strands need to be looked at if the term is to be understood and if those who accuse Buddhist compassion of being too passive are to be answered correctly.
IMO a simple analogy might be that a doctor doesn't need to be ill in order to help their patients -- it's better if they're not.
I also recommend this article on the Brahmaviharas in general (including compassion and equanimity): The Four Sublime States by Nyanaponika Thera.
There's also for example this essay, Toward a Threshold of Understanding, which says that it's a mistake to see Buddhism as "indifference" toward the world:
he Pontiff describes Nibbana as "a state of perfect indifference with regard to the world," adding that in Buddhism salvation means "above all, to free oneself from evil by becoming indifferent to the world, which is the source of evil" (p.86). By such statements he represents Buddhism to his readers as a quietistic doctrine of withdrawal which can address the momentous problems that face humanity today only by politely turning its back on them. This is hardly a satisfactory depiction of Early Buddhism, in which transcendence of the world is stressed, let alone of Mahayana Buddhism, in which the bodhisattva's compassionate activity on behalf of the world becomes the guiding ideal.
The Pali word that the Pope interprets as "indifference" is presumably upekkha. The real meaning of this word is equanimity, not indifference in the sense of unconcern for others. As a spiritual virtue, upekkha means equanimity in the face of the fluctuations of worldly fortune. It is evenness of mind, unshakeable freedom of mind, a state of inner equipoise that cannot be upset by gain and loss, honor and dishonor, praise and blame, pleasure and pain. Upekkha is freedom from all points of self-reference; it is indifference only to the demands of the ego-self with its craving for pleasure and position, not to the well-being of one's fellow human beings. True equanimity is the pinnacle of the four social attitudes that the Buddhist texts call the "divine abodes": boundless loving-kindness, compassion, altruistic joy, and equanimity. The last does not override and negate the preceding three, but perfects and consummates them.
If Buddhism in practice has not always lived up to the high ideals posited by the original Teaching, this is to be understood as a result of the downward gravitational pull of human nature, not as a consequence of any emphasis on apathy and indifference in the pristine Dhamma. The Buddhist texts provide ample evidence that the attainment of Nibbana does not issue in a stolid indifference to the world. The Buddha himself, the ideal model for his followers, led an active life of 45 years after his enlightenment dedicated to the uplift of humanity. Throughout Buddhist history, the great spiritual masters of the Dhamma have emulated the Awakened One's example, heeding his injunction to wander forth "for the welfare and happiness of many, out of compassion for the world, for the good, welfare, and happiness of devas and humans."