3
Operation
APPLY POWER
Prior to applying power, ensure that jumpers JP1 and JP5
are in the desired position, all loads are connected properly,
and all probes are connected properly. Jumpers JP3 and
JP4 can be shunted and removed after power has been
applied.
The V
IN
power supply must be turned on or enabled first.
Likewise, it must always be disabled or turned off last. This
supply can be set from a minimum of 1.2V
DDQ
to a
maximum of 18V. After the V
IN
power supply has been
enabled, the VCC power supply may be enabled. The VCC
power supply must be 5V.
The PGOOD status LED will give a visual indication of the
V
DDQ
regulator level. Table 3 describes the two states of the
LED.
EXAMINE WAVEFORMS
Start-up is immediate following Power On Reset (POR).
Using an oscilloscope or other laboratory equipment, the
ramp-up and/or regulation of the outputs can be studied.
Loading of the outputs can be accomplished through the use
of electronic loads. Any other method, however, will work as
well.
Evaluation Board Design
General
The evaluation board is built on a 2-ounce, four layer printed
circuit board. The board is designed to support a continuous
load of 5A on the V
DDQ
rail and a simultaneous 3A
continuous load on the V
TT
rail while operating at room
temperature and under natural convection cooling. Loading
on V
REF
should not exceed 10mA.
The schematic, bill of material, and the layout plots for the
ISL6539EVAL1 evaluation board are provided at the end of
this application note.
Eval Board Performance
Power-Up
When the V
CC
voltage exceeds the POR level, the ISL6539
will begin the soft-start procedure. Figure 2 shows the start-
up of both the V
DDQ
and V
TT
rails from POR.
Figure 3 shows the start up the V
DDQ
and V
TT
rails through
the enabling of the V
DDQ
regulator.
LED
CONDITION
RESULT
CR1
Green
V
OUT1
WITHIN PGOOD RANGE
(89%-115% of nominal value)
Red
V
OUT1
OUTSIDE PGOOD RANGE
(89-115% of nominal value)
TABLE 3. PGOOD STATUS LED CONDITION INDICATOR
FIGURE 2. POR SOFT-START, VCC = VIN
FIGURE 3. ENABLED SOFT-START
Timebase: 500µs/DIV
V
DDQ
500mV/DIV
V
IN
1V/DIV
V
TT
500mV/DIV
Timebase: 500µs/DIV
V
DDQ
500mV/DIV
V
IN
1V/DIV
V
TT
500mV/DIV
V
EN
5V/DIV
Application Note 1278