ISL6441IRZ-TK Intersil, ISL6441IRZ-TK Datasheet - Page 15

• Manufacturer Part Number: ISL6441IRZ-TK
• Description: IC CTRLR PWM 1.4MHZ DUAL 28-QFN
• Manufacturer: Intersil

Specifications of ISL6441IRZ-TK

• Applications: Power Supplies
• Current - Supply: 2mA
• Voltage - Supply: 5.6 V ~ 24 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-QFN
• Rohs Compliant: YES
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ISL6441IRZ-TKTR

Base-Drive Noise Reduction
The high-impedance base driver is susceptible to system
noise, especially when the linear regulator is lightly loaded.
Capacitively coupled switching noise or inductively coupled
EMI onto the base drive causes fluctuations in the base
current, which appear as noise on the linear regulator’s
output. Keep the base drive traces away from the step-down
converter, and as short as possible, to minimize noise
coupling. A resistor in series with the gate drivers reduces
the switching noise generated by PWM. Additionally, a
bypass capacitor may be placed across the base-to-emitter
resistor. This bypass capacitor, in addition to the transistor’s
input capacitor, could bring in second pole that will
destabilize the linear regulator. Therefore, the stability
requirements determine the maximum base-to-emitter
capacitance.
Layout Guidelines
Careful attention to layout requirements is necessary for
successful implementation of an ISL6441 based DC/DC
converter. The ISL6441 switches at a very high frequency
and therefore the switching times are very short. At these
switching frequencies, even the shortest trace has
significant impedance. Also the peak gate drive current rises
significantly in extremely short time. Transition speed of the
current from one device to another causes voltage spikes
across the interconnecting impedances and parasitic circuit
elements. These voltage spikes can degrade efficiency,
generate EMI, increase device over voltage stress and
ringing. Careful component selection and proper PC board
layout minimizes the magnitude of these voltage spikes.
There are two sets of critical components in a DC/DC
converter using the ISL6441; the switching power
components and the small signal components. The
switching power components are the most critical from a
layout point of view because they switch a large amount of
energy so they tend to generate a large amount of noise.
The critical small signal components are those connected to
sensitive nodes or those supplying critical bias currents. A
multi-layer printed circuit board is recommended.
60
50
40
30
20
10
0.79
0
FIGURE 21. LINEAR CONTROLLER GAIN
0.80
FEEDBACK VOLTAGE (V)
0.81
15
0.82
0.83
0.84
0.85
ISL6441
Layout Considerations
10. Route all high speed switching nodes away from the
11. Create a separate small analog ground plane near the IC.
12. Ensure the feedback connection to output capacitor is
Component Selection Guidelines
MOSFET Considerations
The logic level MOSFETs are chosen for optimum efficiency
given the potentially wide input voltage range and output
power requirements. Two N-Channel MOSFETs are used in
each of the synchronous-rectified buck converters for the
PWM1 and PWM2 outputs. These MOSFETs should be
selected based upon r
and thermal management considerations.
1. The Input capacitors, Upper FET, Lower FET, Inductor
2. Use separate ground planes for power ground and small
3. The loop formed by Input capacitor, the top FET and the
4. Insure the current paths from the input capacitor to the
5. Place The PWM controller IC close to lower FET. The
6. Place VCC_5V bypass capacitor very close to VCC_5V
7. Place the gate drive components BOOT diode and BOOT
8. The output capacitors should be placed as close to the
9. Use copper filled polygons or wide but short trace to
and Output capacitor, should be placed first. Isolate these
power components on the topside of the board with their
ground terminals adjacent to one another. Place the input
high frequency decoupling ceramic capacitor very close
to the MOSFETs.
signal ground. Connect the SGND and PGND together
close of the IC. Do not connect them together anywhere
else.
bottom FET must be kept as small as possible.
MOSFET; to the output inductor and output capacitor are
as short as possible with maximum allowable trace
widths.
LGATE connection should be short and wide. The IC can
be best placed over a quiet ground area. Avoid switching
ground loop current in this area.
pin of the IC and connect its ground to the PGND plane.
capacitors together near controller IC.
load as possible. Use short wide copper regions to
connect output capacitors to load to avoid inductance and
resistances.
connect junction of upper FET, lower FET and output
inductor. Also keep the PHASE node connection to the IC
short. Do not unnecessarily oversize the copper islands
for PHASE node. Since the phase nodes are subjected to
very high dv/dt voltages, the stray capacitor formed
between these islands and the surrounding circuitry will
tend to couple switching noise.
control circuitry.
Connect SGND pin to this plane. All small signal
grounding paths including feedback resistors, current
limit setting resistors and SYNC/SDx pull-down resistors
should be connected to this SGND plane.
short and direct.
DS(ON)
, gate supply requirements,
May 26, 2009
FN9197.3