ISL6558EVAL2 Intersil, ISL6558EVAL2 Datasheet - Page 12

• Manufacturer Part Number: ISL6558EVAL2
• Description: EVAL BOARD W/6605 DRVRS ISL6558
• Manufacturer: Intersil
• Series: Endura™r

Specifications of ISL6558EVAL2

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.35V
• Current - Output: 30A
• Voltage - Input: 4.5 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: HIP6609, ISL6558
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

from reacting to undervoltage or overvoltage conditions at
the proper time.
If the output voltage is not the same as the internal 0.8V
reference, then a resistor divider scaled like the FB resistors
is required as shown is Figure 8. Otherwise, the output
voltage should be tied directly back to the VSEN pin without
a resistor divider.
PGOOD SIGNAL
The undervoltage comparator and overvoltage latch feed
into the power good monitor and are NOR’d together. If
either indicates a fault, the power good monitor triggers the
PGOOD output low. A high on this open drain pin indicates
proper output voltage.
Application Guidelines
Layout Considerations
Layout is very important in high frequency switching
converter design. With MOSFETs switching efficiently at
greater than 100kHz, the resulting current transitions from
one device to another cause voltage spikes across the
interconnecting impedances and parasitic circuit elements.
These voltage spikes can degrade efficiency, radiate noise
into the circuit, and lead to device overvoltage stress.
Careful component layout and printed circuit design
minimizes the voltage spikes in the converter.
As an example, consider the turnoff transition of the PWM
upper MOSFET. Prior to turnoff, the upper MOSFET was
carrying the channel current. During turnoff, current stops
flowing in the upper MOSFET and is picked up by the lower
MOSFET. Any inductance in the switched current path
generates a large voltage spike during the switching interval.
Careful component selection, tight layout of the critical
components, and short, wide circuit traces minimize the
magnitude of voltage spikes.
FIGURE 8. VSEN RESISTOR DIVIDER CONFIGURATION
V
OUT
R
R
FB
FB
R
R
OS
12
OS
VSEN
FB
DROOP
ISL6558
ISL6558
There are two sets of critical components in a DC-DC
converter using a ISL6558 controller and HIP660x gate
drivers. The switching components are the most critical
because they switch large amounts of energy, and therefore
tend to generate equally large amounts of noise. Next are
the small signal components which connect to sensitive
nodes or supply critical bypassing current and signal
coupling.
A multi-layer printed circuit board is recommended. Figure 9
shows the connections of the critical components for one
output channel of the converter. Note that capacitors C
and C
capacitors. Dedicate one solid layer, usually the middle layer
of the PC board, for a ground plane and make all critical
component ground connections with vias to this layer.
Dedicate another solid layer as a power plane and break this
plane into smaller islands of common voltage levels. Keep
the metal runs from the PHASE terminal to the output
inductor short. The power plane should support the input
power and output power nodes. Use copper filled polygons
on the top and bottom circuit layers for the phase nodes.
Use the remaining printed circuit layers for small signal
wiring. The wiring traces from the HIP660x driver to the
power MOSFET gates and source should be sized to carry
at least 1A of current.
The switching components and HIP660x gate drivers should
be placed first. Locate the input capacitors close to the
power switches. Minimize the length of the connections
between the input capacitors, C
Position both the ceramic and bulk input capacitors as close
to the upper MOSFET drain as possible. Locate the output
inductors and output capacitors between the MOSFETs and
the load. Place the HIP660x gate drivers close to their
respective channel MOSFETs.
The critical small signal components include the bypass
capacitors for VCC on the ISL6558 controller as well as
those on VCC and PVCC of the HIP660x gate drivers.
Position the bypass capacitors, C
pins. It is especially important to place the feedback
resistors, R
and C
to the FB and COMP pins. Care should be taken in routing
the current sense lines such that the ISEN resistors are
close to their respective pins on the controller. Resistor R
which sets the oscillator frequency, should be positioned
near the FS/EN pin.
C
OUT
, associated with the input to the error amplifier close
could each represent numerous physical
FB
and R
OS
, and compensation components, R
IN
BP
, and the power switches.
, close to the device
June 21, 2005
FN9027.12
IN
T
C
,