MC3334(V2) Просмотр технического описания (PDF) - Motorola => Freescale
Номер в каталоге
Компоненты Описание
производитель
MC3334 Datasheet PDF : 6 Pages
| |||
MC3334 MCC3334 MCCF3334
CIRCUIT DESCRIPTION
The MC3334 high energy ignition circuit was designed to
serve aftermarket Delco five–terminal ignition applications.
This device, driving a high voltage Darlington transistor, offers
an ignition system which optimizes spark energy at minimum
power dissipation. The IC is pinned–out to permit thick film or
printed circuit module design without any crossovers.
The basic function of an ignition circuit is to permit build–up
of current in the primary of a spark coil, and then to interrupt
the flow at the proper firing time. The resulting flyback action
in the ignition coil induces the required high secondary
voltage needed for the spark. In the simplest systems, fixed
dwell angle produces a fixed duty cycle, which can result in
too little stored energy at high RPM, and/or wasted power at
low RPM. The MC3334 uses a variable DC voltage
reference, stored on CDwell, and buffered to the bottom end of
the reluctor pickup (S1) to vary the duty cycle at the spark
coil. At high RPM, the MC3334 holds the output “off” for
approximately 1.0 ms to permit full energy discharge from the
previous spark; then it switches the output Darlington
transistor into full saturation. The current ramps up at a slope
dictated by Vbat and the coil L. At very high RPM the peak
current may be less than desired, but it is limited by the
coil itself.
As the RPM decreases, the ignition coil current builds up
and would be limited only by series resistance losses. The
MC3334 provides adjustable peak current regulation sensed
by RS and set by RD1, in this case at 5.5 A, as shown in
Figure 2. As the RPM decreases further, the coil current is
held at 5.5 A for a short period. This provides a reserve for
sudden acceleration, when discharge may suddenly occur
earlier than expected. The peak hold period is about 20% at
medium RPM, decreasing to about 10% at very low RPM.
(Note: 333 Hz = 5000 RPM for an eight cylinder four stroke
engine.) At lower Vbat, the “on” period automatically stretches
to accommodate the slower current build–up. At very low Vbat
and low RPM, a common condition during cold starting, the
“on” period is nearly the full cycle to permit as much coil
current as possible.
The output stage of the IC is designed with an OVP circuit
which turns it on at Vbat ≈ 30 V (VCC ≈ 22 V), holding the
output Darlington off. This protects the IC and the Darlington
from damage due to load dump or other causes of
excessive Vbat.
Component Values
Pickup – series resistance = 800 Ω ± 10% @ 25°C
inductance = 1.35 H @ 1.0 kHz @ 15 Vrms
Coil
– leakage L = 0.6 mH
primary R = 0.43 Ω ± 5% @ 25°C
primary L = 7.5 mH to 8.5 mH @ 5.0 A
RL
– load resistor for pickup = 10 kΩ ± 20%
RA, RB – input buffer resistors provide additional
transient protection to the already clamped
inputs = 20 k ± 20%
C1, C2
– for reduction of high frequency noise and
spark transients induced in pick–up and
leads; optional and non–critical
Rbat
– provides load dump protection (but small
enough to allow operation at Vbat = 4.0 V)
= 300 Ω ± 20%
CFilter – transient filter on VCC, non–critical
CDwell – stores reference, circuit designed for 0.1 µF
± 20%
RGain – RGain/RD1 sets the DC gain of the current
regulator = 5.0 k ± 20%
RD2
RS
– RD2/RD1 set up voltage feedback from RS
– sense resistor (PdAg in thick film techniques)
= 0.075 Ω ± 30%
RDrive
– low enough to supply drive to the output
Darlington, high enough to keep VCE(sat) of
the IC below Darlington turn–on during load
dump = 100 Ω ± 20%, 5.0 W
RD1
– starting with 35 Ω assures less than 5.5 A,
increasing as required to set 5.5 A
RD1
=
IO(pk) RS–Vref
Vref – 1.4
– (≈ 100 Ω)
RD2 RGain
General Layout Notes
The major concern in the substrate design should be to
reduce ground resistance problems. The first area of concern
is the metallization resistance in the power ground to module
ground and the output to the Rdrive resistor. This resistance
directly adds to the VCE(sat) of the IC power device and if not
minimized could cause failure in load dump. The second
concern is to reference the sense ground as close to the
ground end of the sense resistor as possible in order to
further remove the sensitivity of ignition coil current to ground
I.R. drops.
All versions were designed to provide the same pin–out
order viewed from the top (component side) of the board or
substrate. This was done to eliminate conductor
cross–overs. The standard MC3334 plastic device is
numbered in the industry convention, counter–clockwise
viewed from the top, or bonding pad side. The MCCF3334
“flip” or “bump” chip is made from reversed artwork, so it is
numbered clockwise viewed from its bump side. Since this
chip is mounted face down, the resulting assembly still has
the same counter–clockwise order viewed from above the
component surface. All chips have the same size and
bonding pad spacing. See Figure 4 for dimensions.
MOTOROLA ANALOG IC DEVICE DATA
3
Share Link: 