ISL6558EVAL2 Intersil, ISL6558EVAL2 Datasheet - Page 5

• Manufacturer Part Number: ISL6558EVAL2
• Description: EVAL BOARD W/6605 DRVRS ISL6558
• Manufacturer: Intersil
• Series: Endura™r

Specifications of ISL6558EVAL2

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.35V
• Current - Output: 30A
• Voltage - Input: 4.5 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: HIP6609, ISL6558
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

Figure 4 shows the efficiency for various frequencies and
airflow conditions.
Different combinations of upper and lower MOSFETs have
been evaluated at Vin = 5V and Fsw = 500kHz with 200LFM
airflow, as shown in Table 5. The last combination with one
Hitachi HAT2164 upper FET and two Siliconix Si4842DY
lower FETs provides high efficiency and good thermal
performance with some space and cost reduction.
OUTPUT SOFT-START AND TURN-OFF
As the control voltage VCC5 reaches the POR rising
threshold (4.38V nominal) of the ISL6558, the FS/EN pin is
released from ground; the output begins a monotonic rise
comprised of 2048 digital steps, as shown in Figure 4. At the
end of the soft-start interval, the PGOOD signal transitions to
indicate the output voltage is within specification.
TABLE 5. EFFICIENCY WITH DIFF. UPPER & LOWER MOSFETs
#
1
2
3
4
FIGURE 4. EFFICIENCY FOR VARIOUS FREQUENCY AND
92
91
90
89
88
87
86
85
FIGURE 5. SOFT-START WAVEFORMS
UPPER FET
HAT2168 x2
HAT2168 x1
HAT2168 x2
HAT2164 x1
5
AIRFLOW AT V
10
F
SW
F
SW
= 465K, 200 LFM
PGOOD
V
IN
= 500K, 200 LFM
=VCC5
15
IN
LOWER FET
Si4842DY x2
Si4842DY x2
HAT2164 x2
HAT2164 x2
5
=5V
Iout (A)
F
SW
= 500K, 0 LFM
V
20
O
25
EFFICIENCY
89.85%
87.94%
89.50%
88.90%
Application Note 1044
30
As shown in Figure 6, the converter is disabled when the
control voltage (VCC5) is pulled below the POR falling
threshold (3.88V nominal) of the ISL6558. The PGOOD
signal falls low indicating the output voltage is out of
regulation. The ISL6609 enters Tri-State® and holds both
upper and lower drive signals low. The L-C resonant tank is
broken and cannot cause negative ringing at the output
since the lower FETs are turned off, blocking any negative
current.
TRANSIENT RESPONSES
A transient load generator is populated on the board to
evaluate the response of the converter at high-speed load
transients. Current setting of the generator provides about
6.5A load step with 160A/µs on the rising edge and 210A/µs
on the falling edge without output droop configuration.
The input current rises/falls at a speed limited by the input
inductor and capacitors during step-up/step-down transients.
Figure 7 shows a very low ramping up speed (0.02A/µs) of
the input current at the load transient condition. This is due
to a large effective input inductance seen by the converter.
The effective input inductance is the sum of the on-board
input inductance and the inductance of the long source leads
of the bench power supply.
The transient performance at different operating conditions
has been summarized in Table 6. Little difference is noted for
various line and load conditions. Note that the ripple portion
has been included.
INPUT VOLTAGE/LOAD CURRENT
TABLE 6. TRANSIENT RESPONSE (6.5A STEP)
FIGURE 6. TURN-OFF WAVEFORMS
4.5V/25A
5.0V/25A
5.5V/25A
4.5V/0A
5.0V/0A
5.5V/0A
V
O
PGOOD
V
IN
=VCC5
I
OUT
STEP-UP/DOWN
21.9mV/21.9mV
21.9mV/21.9mV
21.9mV/23.1mV
22.5mV/21.9mV
21.9mV/21.2mV
23.8mV/24.4mV
April 4, 2006
AN1044.2