Datasheet

5 7 9 11 13 15 17 19 21 23 25 27 29

100

EFFICIENCY (%)

LOAD CURRENT (A)

36V

48V

72V

OUT

= 3.3V

Over Current Protection

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9 Over Current Protection

The evaluation board is configured with hiccup over-current protection. In the event of an output overload

(approximately 38A) the unit will discharge the SS capacitor, which disables the power stage. After a

delay, programmed by the RES capacitor, the SS capacitor is released. If the overload condition persists,

this process is repeated. Thus, the converter will be in a loop of shot bursts followed by a sleep time in

continuous overload conditions. The sleep time reduces the average input current drawn by the power

converter in such a condition and allows the power converter to cool down.

10 Performance Characteristics

Once the circuit is powered up and running normally, the output voltage is regulated to 3.3V with the

accuracy determined by the feedback resistors and the voltage reference. The frequency of operation is

selected to be 420 kHz, which is a good comprise between board size and efficiency, see Figure 3. for

efficiency curves.

Figure 3. Application Board Efficiency

When applying power to the LM5045 evaluation board a certain sequence of events occurs. Soft-start

capacitor values and other components allow for a minimal output voltage for a short time until the

feedback loop can stabilize without overshoot. Figure 4 shows the output voltage during a typical start-up

with a 48V input and a load of 25A. There is no overshoot during start-up.

AN-2111 LM5045 Evaluation Board SNVA468C–February 2011–Revised May 2013

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