ISL6558EVAL1Z Intersil, ISL6558EVAL1Z Datasheet - Page 14

• Manufacturer Part Number: ISL6558EVAL1Z
• Description: EVAL BOARD 1 FOR ISL6558
• Manufacturer: Intersil

Specifications of ISL6558EVAL1Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3. Transient Response with Lo = 650nH and
Added C300 (1000µF)
As shown in Figure 19, the input current is seen to be as
high as 26A, which could cause the input source to
overcurrent trip. Adding an 1000µF input capacitor
parallel to C3 helps supply currents to the converter at
load transients and reduces the peak current by much
as 10A, as shown in Figure 23. Placing the 1000µF
capacitor at the input side of L1 is not as effective on
reducing the input peak current as in previous case, as
shown in Figure 24. In addition, cutting down the input
inductance value, at the cost of higher input current
slew rate, is another possible way to reduce the input
peak current due to load transients. Note that the
effective input inductance seen by the converter is
higher than the on-board input inductor due to the long
source leads of the bench power supply. Hence, users
would see different input current waveforms because of
the difference of the effective input inductance of their
bench setups.
FIGURE 23. TRANSIENT RESPONSE WITH ADDED
FIGURE 24. TRANSIENT RESPONSE WITH ADDED
1000µF IN PARALLEL WITH C3
1000µF AT INPUT CONNECTORS
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O
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I
O
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14
O
(28A/DIV)
(28A/DIV)
Application Note 1029
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OVERCURRENT AND SHORT CIRCUIT
When the converter is momentarily shorted or
overloaded, as shown in Figure 25, the converter runs
hiccup mode with a very narrow duty cycle and long
switching period. PGOOD stays low during the
overcurrent period; it indicates the output voltage is
within regulation limits after the short is removed and
the output completes a soft-start interval.
As shown in Figure 26, the converter can sustain a
permanent short circuit remaining in hiccup modes with
a frequency of 44Hz. The average load current and the
average power dissipation in each power component are
reduced significantly; thus, the converter can stay at a
short without causing any permanent damage or thermal
issues.
FIGURE 25. OVER-LOADED OUTPUT WAVEFORMS
FIGURE 26. SHORT-CIRCUIT WAVEFORMS
V
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PGOOD
PGOOD
V
O
July 31, 2009
AN1029.3