To prevent a transformer from saturation, the V-t product must be greater than the maximum V-t product applied by the device. The maximum voltage delivered by the device is the nominal converter input plus 10%. The maximum time this voltage is applied to the primary is half the period of the lowest frequency at the specified input voltage. Therefore, the minimum V-t product for the transformer is determined through:

Taking an example of f_min as 138kHz for ISO7741TA-Q1 and 363kHZ for ISO7741TB-Q1 with a 5V supply, the following equations yield the minimum V-t products of:

${\mathrm{V}\mathrm{t}}_{\mathrm{m}\mathrm{i}\mathrm{n}}\ge \frac{5.5\mathrm{V}}{2\times 138\mathrm{k}\mathrm{H}\mathrm{z}}=20\mathrm{V}\mathrm{\mu }\mathrm{s}$ for ISO7741TA-Q1 applications, and
${\mathrm{V}\mathrm{t}}_{\mathrm{m}\mathrm{i}\mathrm{n}}\ge \frac{5.5\mathrm{V}}{2\times 363\mathrm{k}\mathrm{H}\mathrm{z}}=7.6\mathrm{V}\mathrm{\mu }\mathrm{s}$ for ISO7741TB-Q1 applications

Common V-t values for low-power center-tapped transformers range from 22Vμs to 150Vμs with typical footprints of 10mm x 12mm. However, transformers specifically designed for PCMCIA applications provide as little as 11Vμs and come with a significantly reduced footprint of 6mm x 6mm only.

While Vt-wise all of these transformers can be driven by the device, other important factors such as isolation voltage, transformer wattage, and turns ratio must be considered before making the final decision.