4
load and the PGOOD signal transitions high once the soft-
start cycle is complete.
Under most circumstances an overcurrent event will remain
until the fault is found and removed. The ISL6553 will
continue to cycle through the same delay time and soft-start
cycle sequence until that time. The worst-case power
delivered during overcurrent cycling is less than that of
normal operation due to the addition of delay time. Indefinite
overcurrent cycling does not create any thermal issues.
Efficiency
The performance of the ISL6553EVAL1 board loaded from
5A to 30A is plotted in Figure 8. The measurements were
made at thermal equilibrium under room temperature
conditions with no air flow.
Adapting Circuit Performance
This evaluation board showcases one solution to meet the
present requirements of voltage regulator modules powering
Intel Pentium III processors. The balance between meeting
specifications and cost can be tilted depending on the
performance expectations desired. For example,
implementation cost could be reduced if additional
motherboard space is available. The OSCON output
capacitors could be replaced with less costly aluminum
capacitors with higher ESR, but more than four capacitors
would be required to meet the same transient specifications.
Efficiency could be improved by selecting MOSFETs with a
slightly lower r
DS(on)
and comparable total gate charge.
Summary
The ISL6553EVAL1 is an adaptable evaluation tool which
showcases the performance of the ISL6553 / HIP6601A chip
set. Designed to meet the performance requirements of
Intel’s VRM-8.5 specification, the board allows the user the
flexibility to configure the board for current as well as future
microprocessor offerings.
The following pages provide a schematic of the board, bill of
materials and layout drawings to support implementation of
this solution.
References
Intersil documents are available on the web at
http://www.intersil.com/.
[1] ISL6553 Data Sheet, Intersil Corporation, FN4931
[2] HIP6601A/HIP6603A Data Sheet, Intersil Corporation,
FN4819
[3] HIP6602A Data Sheet, Intersil Corporation, FN4902
FIGURE 7. RESPONSE TO TEMPORARY OUTPUT SHORT
5ms/div
Core Voltage (1V/div)
Output Current (20A/div)
PGOOD (5V/div)
PWM1 (5V/div)
0V
0A
0V
0V
FIGURE 8. EFFICIENCY vs LOAD CURRENT
OUTPUT CURRENT (A)
10
15
20
25
30
5
70
75
80
85
90
95
EFFICIE
N
CY
(%)
Application Note AN9961
