ISL6522EVAL1 Intersil, ISL6522EVAL1 Datasheet - Page 7

• Manufacturer Part Number: ISL6522EVAL1
• Description: EVALUATION BOARD ISL6522
• Manufacturer: Intersil

Specifications of ISL6522EVAL1

• Main Purpose: DC/DC, Step Down
• Voltage - Input: 10.8 ~ 13.2V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: ISL6522
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Voltage - Output: -
• Power - Output: -
• Frequency - Switching: -
• Outputs And Type: -

Overcurrent Protection
The overcurrent function protects the converter from a
shorted output by using the upper MOSFETs on-resistance,
r
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. An internal 200µA
(typical) current sink develops a voltage across R
DS(ON)
t
0
V
VOLTAGE
OSC(MIN)
15A
10A
4V
2V
5A
0A
t
t
Where:
0V
1
SoftStart
=
to monitor the current. This method enhances the
C
----------- V
I
FIGURE 4. OVERCURRENT OPERATION
SS
SS
FIGURE 3. SOFT-START INTERVAL
C
I
V
V
∆V
V
⋅
=
SS
t
SS
OSC(MIN)
IN
OUTSteadyState
1
OSC
OSC MIN
t
2
= Soft Start Current = 10µA
= Input Voltage
= Soft Start Capacitor
–
t
(
1
= Peak to Peak Oscillator Voltage = 1.9V
t
2
=
= Bottom of Oscillator = 1.35V
C
-----------
)
I
SS
TIME (20ms/DIV)
SS
CLAMP ON V
STEADY STATE
7
= Steady State Output Voltage
⋅
V
------------------------------------------------ ∆V
OUT
SteadyState
V
IN
COMP
V
SOFT START
RELEASED AT
⋅
OCSET
V
COMP
V
OUT
OSC
OCSET
TIME
that
)
ISL6522
is reference to V
MOSFET (also referenced to V
across R
sequence. The soft-start function discharges C
10µA current sink and inhibits PWM operation. The soft-start
function recharges C
the error amplifier clamped to the SS voltage. Should an
overload occur while recharging C
inhibits PWM operation while fully charging C
complete its cycle. Figure 4 shows this operation with an
overload condition. Note that the inductor current increases
to over 15A during the C
overcurrent trip. The converter dissipates very little power
with this method. The measured input power for the
conditions of Figure 4 is 2.5W.
The overcurrent function will trip at a peak inductor current
(I
where I
is typical). The OC trip point varies mainly due to the
MOSFETs r
in the normal operating load range, find the R
from the equation above with:
The maximum r
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 ISL6522 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 ISL6522 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
that is being down-converted. If there is nowhere for this current
to go, such as to other distributed loads on the V
a voltage limiting protection device, or other methods, the
capacitance on the V
situation will cause the voltage level of the V
the voltage level of the rail is boosted to a level that exceeds the
maximum voltage rating of the MOSFETs or the input
capacitors, damage may occur to these parts. If the bias
voltage for the ISL6522 comes from the V
I
1. The minimum I
2. Determine
PEAK
PEAK)
OCSET
where ∆I is the output inductor ripple current.
=
OCSET
determined by:
OCSET
to smooth the voltage across R
I
-------------------------------------------------- -
OCSET
DS(ON)
r
DS ON
is the internal OCSET current source (200µA
I
DS(ON)
, the overcurrent function initiates a soft-start
PEAK
IN
•
(
. When the voltage across the upper
R
OCSET
variations. To avoid overcurrent tripping
OCSET
IN
SS
)
for I
bus will absorb the current. This
at the highest junction temperature.
, and PWM operation resumes with
SS
PEAK
from the specification table.
charging interval and causes an
IN
>
I
) exceeds the voltage
OUT MAX
SS
, the soft-start function
(
IN
OCSET
IN
IN
)
rail, then the
rail, the voltage
+
rail to increase. If
OCSET
(
SS
∆I
IN
SS
) 2 ⁄
in the
rail, through
to 4V to
March 10, 2006
with a
,
resistor
FN9030.8