IXDP631 Ver la hoja de datos (PDF) - IXYS CORPORATION
Número de pieza
componentes Descripción
Fabricante
IXDP631 Datasheet PDF : 7 Pages
| |||
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
© 1998 IXYS All rights reserved
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, VOL, 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
I - 19
Share Link: 