ISL6526EVAL2

Manufacturer Part NumberISL6526EVAL2
DescriptionEVALUATION BOARD QFN ISL6526
ManufacturerIntersil
ISL6526EVAL2 datasheet
 


Specifications of ISL6526EVAL2

Main PurposeDC/DC, Step DownOutputs And Type1, Non-Isolated
Voltage - Output2.5VCurrent - Output5A
Voltage - Input3.3 ~ 5VRegulator TopologyBuck
Frequency - Switching300kHzBoard TypeFully Populated
Utilized Ic / PartISL6526Lead Free Status / RoHS StatusContains lead / RoHS non-compliant
Power - Output-  
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(such as to other distributed loads on the rail or through a
voltage limiting protection device), the capacitance on this
rail will absorb the current. This situation will allow the
voltage level of the input rail to increase. If the voltage level
of the rail is boosted to a level that exceeds the maximum
voltage rating of any components attached to the input rail,
then those components may experience an irreversible
failure or experience stress that may shorten their lifespan.
Ensuring that there is a path for the current to flow other than
the capacitance on the rail will prevent this failure mode.
Application Guidelines
Layout Considerations
Layout is very important in high frequency switching
converter design. With power devices switching efficiently at
300kHz or 600kHz, the resulting current transitions from one
device to another cause voltage spikes across the
interconnecting impedances and parasitic circuit elements.
These voltage spikes can degrade efficiency, radiate noise
into the circuit, and lead to device overvoltage stress.
Careful component layout and printed circuit board design
minimize the voltage spikes in the converters.
As an example, consider the turn-off transition of the PWM
MOSFET. Prior to turn-off, the MOSFET is carrying the full load
current. During turn-off, current stops flowing in the MOSFET
and is picked up by the lower MOSFET. Any parasitic
inductance in the switched current path generates a large
voltage spike during the switching interval. Careful component
selection, tight layout of the critical components, and short, wide
traces minimize the magnitude of voltage spikes.
There are two sets of critical components in a DC/DC
converter using the ISL6526, ISL6526A. The switching
components are the most critical because they switch large
amounts of energy, and therefore tend to generate large
amounts of noise. Next are the small signal components
which connect to sensitive nodes or supply critical bypass
current and signal coupling.
A multi-layer printed circuit board is recommended. Figure 4
shows the connections of the critical components in the
converter. Note that capacitors C
and C
IN
represent numerous physical capacitors. Dedicate one solid
layer (usually a middle layer of the PC board) for a ground
plane and make all critical component ground connections
with vias to this layer. Dedicate another solid layer as a
power plane and break this plane into smaller islands of
common voltage levels. Keep the metal runs from the
PHASE terminals to the output inductor short. The power
plane should support the input power and output power
nodes. Use copper filled polygons on the top and bottom
circuit layers for the phase nodes. Use the remaining printed
circuit layers for small signal wiring. The wiring traces from
the GATE pins to the MOSFET gates should be kept short
and wide enough to easily handle the 1A of drive current.
9
ISL6526, ISL6526A
ISL6526, ISL6526A
FIGURE 4. PRINTED CIRCUIT BOARD POWER PLANES
The switching components should be placed close to the
ISL6526, ISL6526A first. Minimize the length of the connections
between the input capacitors, C
placing them nearby. Position both the ceramic and bulk input
capacitors as close to the upper MOSFET drain as possible.
Position the output inductor and output capacitors between the
upper MOSFET and lower MOSFET and the load.
The critical small signal components include any bypass
capacitors, feedback components, and compensation
could each
OUT
components. Position the bypass capacitor, C
the VCC pin with a via directly to the ground plane. Place the
PWM converter compensation components close to the FB
and COMP pins. The feedback resistors for both regulators
should also be located as close as possible to the relevant
FB pin with vias tied straight to the ground plane as required.
Feedback Compensation
Figure 5 highlights the voltage-mode control loop for a
synchronous-rectified buck converter. The output voltage
(V
) is regulated to the Reference voltage level. The
OUT
error amplifier (Error Amp) output (V
the oscillator (OSC) triangular wave to provide a pulse
width modulated (PWM) wave with an amplitude of V
+3.3V V
IN
VCC
C
VCC
CPVOUT
C
BP
C
IN
GND
D1
BOOT
C
BOOT
Q1
UGATE
L
OUT
V
PHASE
PHASE
Q2
C
LGATE
OUT
COMP
C
2
C
1
R
2
R
1
FB
C
R
3
3
R4
KEY
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT PLANE LAYER
VIA CONNECTION TO GROUND PLANE
AND ISLANDS
, and the power switches by
IN
, close to
BP
) is compared with
E/A
November 24, 2008
OUT
at
IN
FN9055.10