HIP6311A

FN9035 Rev 1.00

Page 13 of 16

July 2004

As discussed previously, the voltage drop across each Q2

pin. This pin is held at virtual ground, so the current into ISEN

is:

Example: From the previous conditions,

= 100A,

= 25.49A,

= 4m



= 2.04K and

Channel Frequency Oscillator

The channel oscillator frequency is set by placing a resistor,

this resistor next to the pin. If this pin is also used to disable the

converter, it is also important to locate the pull-down device

next to this pin.

Layout Considerations

MOSFETs switch very fast and efficiently. The speed with

which the current transitions from one device to another

causes 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 over-voltage stress. Careful component layout and

printed circuit design minimizes the voltage spikes in the

converter. Consider, as an example, the turnoff transition of

the upper PWM MOSFET. Prior to turnoff, the upper MOSFET

was carrying channel current. During the 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. Contact Intersil for evaluation

board drawings of the component placement and printed circuit

board.

There are two sets of critical components in a DC-DC

converter using a HIP6311A controller and a HIP6601 gate

driver. The power components are the most critical because

they switch large amounts of energy. Next are small signal

components that connect to sensitive nodes or supply critical

bypassing current and signal coupling.

The power components should be placed first. Locate the input

capacitors close to the power switches. Minimize the length of

power switches. Locate the output inductors and output

capacitors between the MOSFETs and the load. Locate the

gate driver close to the MOSFETs.

The critical small components include the bypass capacitors

for VCC and PVCC on the gate driver ICs. Locate the bypass

device. It is especially important to locate the resistors

associated with the input to the amplifiers close to their

respective pins, since they represent the input to feedback

should also be located next to the associated pin. It is

respective terminals of the HIP6311A.

A multi-layer printed circuit board is recommended. Figure 11

shows the connections of the critical components for one output

could each represent numerous physical 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

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 driver IC to the MOSFET gate

and source should be sized to carry at least one ampere of

current.

50

100

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500 1,000

5,000 10,000

2,000

1

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1,000