ISL8105BEVAL1Z Intersil, ISL8105BEVAL1Z Datasheet - Page 10

• Manufacturer Part Number: ISL8105BEVAL1Z
• Description: EVAL BOARD ISL8105B
• Manufacturer: Intersil

Specifications of ISL8105BEVAL1Z

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 15A
• Voltage - Input: 9.6 ~ 14.4V
• Regulator Topology: Buck
• Frequency - Switching: 300kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ISL8105B
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

Another consideration for high V
duty cycles (such as 20V in to 1.0V out, for 5% duty cycle)
require component selection compatible with that choice
(such as low r
output filter). At the other extreme (for example, 20V in to
12V out), the top-side MOSFET needs to be low r
addition, if the duty cycle gets too high, it can affect the
overcurrent sample time. In all cases, the input and output
capacitors and both MOSFETs must be rated for the
voltages present.
BOOT Refresh
In the event that the TGATE is on for an extended period of
time, the charge on the boot capacitor can start to sag,
raising the r
has a circuit that detects a long TGATE on-time (nominal
100µs), and forces the BGATE to go high for one clock
cycle, which will allow the boot capacitor some time to
recharge. Separately, the OCP circuit has a BGATE pulse
stretcher (to be sure the sample time is long enough), which
can also help refresh the boot. But if OCP is disabled (no
current sense resistor), the regular boot refresh circuit will
still be active.
Current Sinking
The ISL8105B incorporates a MOSFET shoot-through
protection method which allows a converter to sink current
as well as source current. Care should be exercised when
designing a converter with the ISL8105B when it is known
that the converter may sink current.
When the converter is sinking current, it is behaving as a
boost converter that is regulating its input voltage. This
means that the converter is boosting current into the V
If there is nowhere for this current to go, such as to other
distributed loads on the V
protection device, or other methods, the capacitance on the
V
voltage level of the V
voltage level of the LX is increased to a level that exceeds
the maximum voltage rating of the ISL8105B, then the IC will
experience an irreversible failure and the converter will no
longer be operational. Ensuring that there is a path for the
current to follow other than the capacitance on the rail will
prevent this failure mode.
Application Guidelines
Layout Considerations
As in any high-frequency switching converter, layout is very
important. Switching current from one power device to another
can generate voltage transients across the impedances of the
interconnecting bond wires and circuit traces. These
interconnecting impedances should be minimized by using
wide, short printed circuit traces. The critical components
should be located as close together as possible using ground
plane construction or single point grounding.
IN
bus will absorb the current. This situation will allow
DS(ON)
DS(ON)
of the top-side MOSFET. The ISL8105B
IN
bottom-side MOSFET, and a good LC
rail (also LX) to increase. If the
IN
rail, through a voltage limiting
10
IN
is duty cycle. Very low
DS(ON)
IN
rail.
. In
ISL8105B
Figure 7 shows the critical power components of the
converter. To minimize the voltage overshoot/undershoot,
the interconnecting wires indicated by heavy lines should be
part of ground or power plane in a printed circuit board. The
components shown in Figure 8 should be located as close
together as possible. Please note that the capacitors C
and C
Locate the ISL8105B within three inches of the MOSFETs,
Q
source connections from the ISL8105B must be sized to
handle up to 1A peak current.
Proper grounding of the IC is important for correct operation
in noisy environments. The GND pin should be connected to
a large copper fill under the IC which is subsequently
connected to board ground at a quiet location on the board,
typically found at an input or output bulk (electrolytic)
capacitor.
Figure 8 shows the circuit traces that require additional
layout consideration. Use single point and ground plane
construction for the circuits shown. Locate the resistor,
R
current source is only 21.5µA. Minimize the loop from any
pulldown transistor to reduce antenna effect. Provide local
decoupling between VBIAS and GND pins as described
BSOC
1
ISL8105B
FIGURE 7. PRINTED CIRCUIT BOARD POWER AND
FIGURE 8. PRINTED CIRCUIT BOARD SMALL SIGNAL
and Q
O
BGATE/BSOC
, close to the BGATE/BSOC pin as the internal BSOC
each represent numerous physical capacitors.
ISL8105B
GND
2
BGATE
. The circuit traces for the MOSFETs’ gate and
TGATE
PGND
GROUND PLANES OR ISLANDS
LAYOUT GUIDELINES
LX
GND
LX
C
V
BOOT
BIAS
BOOT
+V
BIAS
V
Q
Q
RETURN
IN
2
1
C
VBIAS
C
Q
+V
IN
Q
1
2
IN
L
O
L
C
O
C
O
O
V
OUT
April 15, 2010
FN6447.2
V
IN
OUT