ISL6526EVAL1 Intersil, ISL6526EVAL1 Datasheet - Page 8

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ISL6526EVAL1

Manufacturer Part Number
ISL6526EVAL1
Description
EVALUATION BOARD SOIC ISL6526
Manufacturer
Intersil
Datasheet

Specifications of ISL6526EVAL1

Main Purpose
DC/DC, Step Down
Outputs And Type
1, Non-Isolated
Voltage - Output
2.5V
Current - Output
5A
Voltage - Input
3.3 ~ 5V
Regulator Topology
Buck
Frequency - Switching
300kHz
Board Type
Fully Populated
Utilized Ic / Part
ISL6526
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Power - Output
-
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
voltage across the upper MOSFET (also referenced to V
exceeds the voltage across R
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.
ISL6526A
+3.3V
ISL6526,
FIGURE 2. OUTPUT VOLTAGE SELECTION
VCC
OCSET
CPVOUT
BOOT
UGATE
PHASE
LGATE
FB
COMP
that is referenced to V
C2
D1
C4
OCSET
C1
8
VIN
R2
Q2
Q1
, the overcurrent function
L
OUT
C
R4
OUT
R1
C3
+
IN
. When the
R3
V
OCSET
ISL6526, ISL6526A
DS(ON)
OUT
IN
)
)
,
The overcurrent function will trip at a peak inductor current
(I
where I
typical). The OC trip point varies mainly due to the MOSFET
r
normal operating load range, find the R
Equation 3 with:
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
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,
I
DS(ON)
1. The maximum r
2. The minimum I
3. Determine I
PEAK)
PEAK
OCSET
0V
temperature.
where ΔI is the output inductor ripple current.
FIGURE 3. OVERCURRENT PROTECTION RESPONSE
=
OCSET
determined by Equation 3:
variations. To avoid overcurrent tripping in the
t0
to smooth the voltage across R
I
---------------------------------------------------- -
OCSET
V
INTERNAL SOFT-START FUNCTION
OUT
r
is the internal OCSET current source (20µA
DS ON
PEAK
x R
(
(2.5V)
DELAY INTERVAL
OCSET
DS(ON)
OCSET
for
)
I
from the specification table.
PEAK
at the highest junction
TIME
>
I
OUT MAX
(
OCSET
OCSET
t1
)
+
(
--------- -
November 24, 2008
resistor from
ΔI
2
in the
)
,
t2
FN9055.10
(EQ. 3)

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