ISL6439IR Intersil, ISL6439IR Datasheet - Page 8

• Manufacturer Part Number: ISL6439IR
• Description: IC CTRLR PWM SYNC BUCK 16-QFN
• Manufacturer: Intersil

Specifications of ISL6439IR

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 340kHz
• Duty Cycle: 100%
• Voltage - Supply: 3.3 V ~ 5 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-VQFN Exposed Pad, 16-HVQFN, 16-SQFN, 16-DHVQFN
• Frequency-max: 340kHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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
diagrams on pages 2 and 3). An internal 20μA (typical) current
sink develops a voltage across R
V
referenced to V
overcurrent function 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 over current still been present after the
delay interval, the over current 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.
The overcurrent function will trip at a peak inductor current
(I
where I
typical). The OC trip point varies mainly due to the MOSFET
I
IN
PEAK)
PEAK
. When the voltage across the upper MOSFET (also
OCSET
+3.3V
=
determined by Equation 3:
ISL6439
FIGURE 2. OUTPUT VOLTAGE SELECTION
I
---------------------------------------------------- -
VCC
OCSET
r
is the internal OCSET current source (20μA
IN
DS ON
) exceeds the voltage across R
x R
(
CPVOUT
BOOT
UGATE
PHASE
LGATE
FB
COMP
OCSET
)
C2
D1
C4
C1
8
VIN
R2
OCSET
Q2
Q1
L
OUT
C
R4
OUT
that is referenced to
R1
C3
+
OCSET
R3
V
OCSET
ISL6439, ISL6439A
OUT
(EQ. 3)
, the
)
r
normal operating load range, find the R
the equation above with:
For an equation for the ripple current see the section under
component guidelines titled ‘Output Inductor Selection’.
A small ceramic capacitor should be placed in parallel with
R
presence of switching noise on the input voltage.
Current Sinking
The ISL6439 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 ISL6439 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,
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
DS(ON)
1. The maximum r
2. The minimum I
3. Determine I
OCSET
0V
temperature.
where ΔI is the output inductor ripple current.
FIGURE 3. OVER CURRENT PROTECTION RESPONSE
variations. To avoid overcurrent tripping in the
T0
to smooth the voltage across R
V
OUT
PEAK
Internal Soft-Start Function
(2.5V)
OCSET
DS(ON)
Delay Interval
for
I
PEAK
from the specification table.
at the highest junction
TIME
>
I
OUT MAX
(
OCSET
OCSET
T1
)
+
(
--------- -
resistor from
ΔI
2
November 5, 2008
in the
)
,
T2
FN9057.5