IXDP630PI datasheet(6/7 Pages) IXYS

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IXDP630

IXDP631

IXDP630 RC Oscillator Component

Details

The IXDP630 oscillator has only two

external components. Rosc should be

a precision, high frequency resistor.

The material used in carbon compo-

sition resistors is hydroscopic (it

absorbs water), causing resistors

above 100 kΩ to 1 MΩ to change value

with relative humidity. This is on top of

initial tolerance and temperature

coefficient deviations, and so is not

recommended. Instead, precision

metal film or carbon film resistor

construction is preferred, with initial

tolerances of 1 % and better with

temperature coefficients of ±100 ppm.

The construction of Cosc is also critical

to circuit operation. Cosc should be a

good quality monolithic ceramic (single

or multilayer) or a metallized polypropy-

lene timing capacitor. If ceramic techno-

logy is chosen, be sure to consider

temperature coefficient and tolerance. It

is the minimum capacitor value that is

critical, not the part number rated

capacitance. A Z5U ceramic has an

initial tolerance of +80/-20 %, and a

temperature variation of +30/-80 %

over temperature. An X7R is ±10 %

initial tolerance, ±10 % over

temperature. An NPO is ±5 % initial

tolerance, ±5 % over temperature

(although tighter selections are readily

available in NPO).

If film technology is chosen, polypropy-

lene is one of the best choices.

Tolerances down to 1 % and 2 % are

standard and temperature coefficient is

±100 ppm.

The layout of the external components

is also critical. The components should

be as close to the device as possible,

minimizing stray capacitance and

inductance.

Fig. 5. Recommended Crystal

Oscillator Components

IXDP631 Crystal Oscillator

Component Details

The IXDP631 oscillator requires three

external passive components, in

addition to the crystal. The crystal is

chosen with a frequency below fclk

(min). The capacitors and resistor

(illustrated earlier in Fig. 5) follow rules

similar to the RC oscillator option. The

resistor should be metal or carbon film,

although its accuracy and stability do

not significantly affect oscillator

frequency accuracy. The capacitors

should be monolithic ceramic

construction (CK05, or similar) with

X7R or better characteristics.

Grounding, Interfacing and Noise

Immunity

Due to the very high level of currents

that are switched at high speed in a

typical motor control power circuit,

voltage transients (V = L di/dt) can

cause serious problems. Fast digital

circuits respond to transients instead of

legitimate inputs, disturbing inverter

operation or causing outright failure.

Bypassing and Decoupling

As with any high speed logic compo-

nent, the IXDP630/631 should be

bypassed with a good quality (mono-

lithic ceramic or film) capacitor designed

specifically for bypass application.

Decoupling is normally not required.

The IXDP630 does not generate

sufficient supply line current ripple to be

a significant noise source when

properly bypassed, and it is capable of

rejecting normal supply line noise.

Logic Levels

All inputs to the IXDP630 and IXDP631

(except XTLIN on the IXDP631) are

HCMOS Schmitt Trigger compatible.

On the IXDP631, the XTLIN pin is

different because the crystal oscillator

circuit cannot tolerate a Schmitt input.

The hysteresis inherent in Schmitt

Trigger inputs greatly improves the

reliability of digital communications. It

can reject ground bounce of up to 2 V,

and induced voltages in digital signal

traces of 1 V.

Power Circuit Noise Generation

In a typical transistor inverter, the

output MOSFET may switch on or off

with di/dt ≥ 500A/µs. Referring to Fig. 6,

and assuming that the MOSFET

Source Terminal has a 1 inch path on

the PCB to system ground, a voltage as

high as 13.5 V can be developed:

V = 27 nH 500A/µs = 13.5 V

If the MOSFET switches 25 A, the

transient will last as long as (25/500) µs

or 50 ns, which is much more than the

typical 6 or 7 ns propagation delay of a

74 HC series gate.

Caution: If one set of digital circuits is

tied to system ground, and one to local

ground, it is clear that such a transient

would cause spurious outputs. In an

inverter, the consequences of such an

error could be catastrophic. Turning a

transistor on at the wrong time could

easily cause it to explode, with the

potential for equipment damage and

operator injury -- clearly undesirable.

Fig. 6. Power circuit noise generation

Methods of Correcting these

Problems

The first step is to use a logic family

with inherent noise immunity. Standard

TTL (or any of its derivatives, including

74HCT CMOS) is a poor choice

because of the logic levels these fami-

lies employ. In particular, V

OL, VIL are too

close to ground to reject the levels of

ground noise common to power circuits.

74HC logic is significantly superior, and

the older 4000 series CMOS is even

better. Unfortunately, in modern motor

controls, especially those that employ

microprocessors, the speeds of the

4000 series CMOS are no longer

adequate. In most cases 74HC logic is

the only viable alternative.

Layout

The second, and most important step is

the printed circuit board (PCB) layout.

The PCB is a very important compo-

nent in any power circuit, and there is a

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