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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+3.3V
VIN
VCC
CPVOUT
D1
BOOT
C4
Q1
UGATE
ISL6526,
L
ISL6526A
PHASE
Q2
LGATE
FB
C1
COMP
C2
R2
FIGURE 2. OUTPUT VOLTAGE SELECTION
Overcurrent Protection
The overcurrent function protects the converter from a shorted
output by using the upper MOSFET ON-resistance, r
to monitor the current. This method enhances the converter’s
efficiency and reduces cost by eliminating a current sensing
resistor.
The overcurrent function cycles the soft-start function in a
hiccup mode to provide fault protection. A resistor (R
programs the overcurrent trip level (see “Typical Application -
3.3V Input” on page 3 and “Typical Application - 5V Input” on
page 3). An internal 20µA (typical) current sink develops a
voltage across R
that is referenced to V
OCSET
voltage across the upper MOSFET (also referenced to V
exceeds the voltage across R
, the overcurrent function
OCSET
initiates a soft-start sequence.
Figure 3 illustrates the protection feature responding to an
overcurrent event. At time t0, an overcurrent condition is
sensed across the upper MOSFET. As a result, the regulator
is quickly shutdown and the internal soft-start function begins
producing soft-start ramps. The delay interval seen by the
output is equivalent to three soft-start cycles. The fourth
internal soft-start cycle initiates a normal soft-start ramp of the
output, at time t1. The output is brought back into regulation
by time t2, as long as the overcurrent event has cleared.
Had the cause of the overcurrent still been present after the
delay interval, the overcurrent condition would be sensed and
the regulator would be shut down again for another delay
interval of three soft-start cycles. The resulting hiccup mode
style of protection would continue to repeat indefinitely.
8
ISL6526, ISL6526A
0V
OUT
V
OUT
+
C
OUT
R1
R3
C3
R4
FIGURE 3. OVERCURRENT PROTECTION RESPONSE
The overcurrent function will trip at a peak inductor current
(I
PEAK)
I
,
PEAK
DS(ON)
where I
typical). The OC trip point varies mainly due to the MOSFET
r
DS(ON)
normal operating load range, find the R
)
OCSET
Equation 3 with:
1. The maximum r
temperature.
. When the
IN
2. The minimum I
)
IN
3. Determine I
where ΔI is the output inductor ripple current.
For the ripple current, see Equation 11 in “Output Inductor
Selection” on page 11.
A small ceramic capacitor should be placed in parallel with
R
OCSET
presence of switching noise on the input voltage.
Current Sinking
The ISL6526, ISL6526A incorporate 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 ISL6526, ISL6526A 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 input
rail of the regulator. If there is nowhere for this current to go,
V
(2.5V)
OUT
INTERNAL SOFT-START FUNCTION
DELAY INTERVAL
t1
t0
TIME
determined by Equation 3:
I
x R
OCSET
OCSET
---------------------------------------------------- -
=
r
(
)
DS ON
is the internal OCSET current source (20µA
OCSET
variations. To avoid overcurrent tripping in the
OCSET
at the highest junction
DS(ON)
from the specification table.
OCSET
>
I
I
+
for
(
)
PEAK
PEAK
OUT MAX
to smooth the voltage across R
OCSET
t2
(EQ. 3)
resistor from
(
ΔI
)
--------- -
,
2
in the
FN9055.10
November 24, 2008