ISL6520IR-T Intersil, ISL6520IR-T Datasheet - Page 5

• Manufacturer Part Number: ISL6520IR-T
• Description: IC CTRLR PWM SYNC BUCK 16-QFN
• Manufacturer: Intersil

Specifications of ISL6520IR-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 340kHz
• Duty Cycle: 100%
• Voltage - Supply: 4.5 V ~ 5.5 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

Start interval and causes an over-current trip. The converter
dissipates very little power with this method. The measured
input power for the conditions of Figure 1 is only 1.5W.
The over-current function will trip at a peak inductor current
(I
where I
typical). The OC trip point varies mainly due to the
MOSFET’s r
in the normal operating load range, find the R
from the equation above with:
For an equation for the ripple current, see“Output Inductor
Selection” on page 7.
Soft-Start
The POR function initiates the soft-start sequence after the
overcurrent set point has been sampled. Soft-start clamps the
error amplifier output (COMP pin) and reference input (non-
inverting terminal of the error amp) to the internally generated
Soft-Start voltage. Figure 2 shows a typical start up interval
where the COMP/OCSET pin has been released from a
grounded (system shutdown) state. Initially, the COMP/OCSET
is used to sample the oversurrent setpoint by disabling the error
amplifier and drawing 20μA through R
current level has been sampled, the soft start function is
initiated. The clamp on the error amplifier (COMP/OCSET pin)
initially controls the converter’s output voltage during soft start.
The oscillator’s triangular waveform is compared to the ramping
error amplifier voltage. This generates PHASE pulses of
increasing width that charge the output capacitor(s). When the
internally generated Soft-Start voltage exceeds the feedback
I
PEAK
1. The maximum r
2. The minimum I
3. Determine I
PEAK)
temperature.
where ΔI is the output inductor ripple current.
=
OCSET
determined by:
I
---------------------------------------------------- -
OCSET
FIGURE 1. OVERCURRENT OPERATION
DS(ON)
r
is the internal OCSET current source (20μA
DS ON
PEAK
x R
(
OUTPUT INDUCTOR
OCSET
DS(ON)
variations. To avoid over-current tripping
OCSET
)
for
CURRENT
5A/DIV.
TIME (5ms/DIV.)
from the specification table.
at the highest junction
I
PEAK
5
>
I
OUT MAX
OCSET
(
. Once the over-
OCSET
)
+
(
--------- -
ΔI
2
)
resistor
,
(EQ. 3)
ISL6520
(FB pin) voltage, the output voltage is in regulation. This
method provides a rapid and controlled output voltage rise. The
entire startup sequence typically take about 11ms.
Application Guidelines
Layout Considerations
As in any high frequency switching converter, layout is very
important. Switching current from one power device to another
can generate voltage transients across the impedances of the
interconnecting bond wires and circuit traces. These
interconnecting impedances should be minimized by using
wide, short printed circuit traces. The critical components
should be located as close together as possible, using ground
plane construction or single point grounding.
Figure 3 shows the critical power components of the converter.
To minimize the voltage overshoot, the interconnecting wires
indicated by heavy lines should be part of a ground or power
plane in a printed circuit board. The components shown in
Figure 3 should be located as close together as possible.
Please note that the capacitors C
represent numerous physical capacitors. Locate the ISL6520
within 3 inches of the MOSFETs, Q
for the MOSFETs’ gate and source connections from the
ISL6520 must be sized to handle up to 1A peak current.
FIGURE 3. PRINTED CIRCUIT BOARD POWER AND
ISL6520
COMP/OCSET
UGATE
PHASE
LGATE
1V/DIV.
GROUND PLANES OR ISLANDS
FIGURE 2. START UP SEQUENCE
TIME (2ms/DIV.)
Q
V
Q
RETURN
2
IN
1
IN
1
and C
and Q
C
O
IN
2
may each
. The circuit traces
L
500mV/DIV.
O
V
C
OUT
O
V
OUT
April 3, 2007
FN9009.6