is desired to power down the whole system in a fault condition, then WDO may be tied to the KILL pin. In this case, WDO will pull KILL low and a Hard Reset will be initiated. After 200ms, if no transition is detected on WDI, then WDO will release KILL and the system will be allowed to power up again. In this case, it is important to note that the timing capacitor (CT pin) must be sized such that the system can power up and assert a WDI transition in less than 1.5s (the watchdog timeout time) minus the hard reset time (1s for a 0.01uF CT capacitor). If a less drastic system reset is desired, then the WDO pin may be used to pull down on the EN pins of any power supplies that are to be reset. In this case, the EN pins will be forced low for 200ms after which they will be released and can be driven high if so desired. It is important to note that the EN pins are not driven with a low impedance output.
Suppressing radiated & Conducted emissions
The LTC3375 PWM switching frequency is specifically trimmed to 2MHz with a guaranteed range of 1.8MHz to 2.2MHz with a 400k RT resistor. The RT resistor can be used to program any operating frequency between 1 and 3MHz. The regulators can also be set to a forced continuous PWM operating mode to prevent operation in Burst Mode operation even at light loads. This not only keeps the frequency fixed but also reduces voltage ripple on the DC-DC output capacitors. Further the LTC3375 can be synchronized with an external clock ranging from 1 to 3 MHz through the SYNC pin to further reduce system noise.
The LTC3375 includes a special feature which allows the user to slow down the switching edge rates to reduce radiated emissions. Source suppression uses layout/component selection to prevent the