In AD8542's D/S, DMAX is 97%. Would it be available both charge mode and discharge mode ? We consider DC in as +48V and DC out as +1.5V for battery. In this case the maximum duty would be 96.8% at discharge mode. How much is minimum on time at charge mode (buck converter) ?
The max duty cycle is available for both charge and discharge modes. The minimum on time in either mode is determined by 100% - DMAX then shortening it further by 2*DT, where DT is the dead time (see Fig 46 in data sheet). DT is programmed with a resistor to DT pin using either Fig 28 or equation on page 32 of the data sheet.
Hope this helps.