increased to 68nF, resulting in a lower peak input current
of 350mA with a VOUT ramp time of 1.6ms. CSS or RSS can
be increased further for an even slower ramp, if desired.
Diode D2 serves to quickly discharge CSS when VSS is
driven low to shut down the device. D2 can be omitted,
resulting in a “soft-stop” slow discharge of the output
Figure 8. RSS = 15k, CSS = 33nF; VOUT Reaches – 5V in 1ms;
Input Current Peaks at 500mA
Figure 9. RSS = 15k, CSS = 68nF; VOUT Reaches – 5V in 1.6ms;
Input Current Peaks at 350mA
Figure 10. Suggested Component Placement.
Note Cut in Ground Copper at D1’s Cathode
APPLICATIO S I FOR ATIO
A Schottky diode is recommended for use with the LT1931/
LT1931A. The Motorola MBR0520 is a very good choice.
Where the input to output voltage differential exceeds 20V,
use the MBR0530 (a 30V diode). These diodes are rated to
handle an average forward current of 0.5 A. In applications
where the average forward current of the diode exceeds
0.5A, a Microsemi UPS5817 rated at 1A is recommended.
The high-speed operation of the LT1931/LT1931A de-
mands careful attention to board layout. You will not get
advertised performance with careless layout. Figure 10
shows the recommended component placement. The
ground cut at the cathode of D1 is essential for low noise