MC33099 View Datasheet(PDF) - Motorola => Freescale
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MC33099 Datasheet PDF : 13 Pages
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MC33099
APPLICATION CIRCUIT DESCRIPTION
Introduction
The MC33099 is an alternator voltage regulator designed
with internal level shifting resistors to control the voltage in a
12V automotive system that uses a 3 phase alternator with a
rotating field winding. The system shown in Figure 1 includes
an alternator with its associated field coil, stator coils and
rectifiers, an automotive battery, a fault indicator lamp, an
ignition switch, a field flyback diode and the MC33099.
The 12V system voltage (Vbat) is connected to a Remote
input by a remote wire which provides the IC regulator with an
external Kelvin connection directly to the battery to provide
Remote voltage, Vrem. The system voltage at the Batt
terminal is also sensed by an internal Local IC connection as
Local voltage Vl. The Local connection is provided in the
event the remote wire or remote connection becomes faulty
such as being resistive, an open or shorted to ground.
The Phase input is normally connected to a tap on one
corner of the alternator’s stator winding which provides an
AC phase voltage (Vph) for the IC to determine the rotational
frequency (fph) of the alternator rotor. Two frequency
comparators (F1 and F2) monitors voltage Vph to determine
a phase rotation detection frequency (f1) and a Low/High
RPM transition phase frequency (f2) respectively. A phase
filter pin 13 is provided for externally providing a filter
capacitance for filtering phase input noise.
The regulated DC system set voltage (Vset) is achieved by
employing feedback to compare a ratioed value of Vset to an
internal IC bandgap voltage reference having a negative
temperature coefficient (TC). The gate drive of an external
N–channel MOSFET is regulated by the IC to control the field
current in the alternator field coil as an alternating ON or OFF
state dependent on load current conditions affecting voltage
Vset. The external MOSFET receives gate–to–source voltage
drive from between the Gate and Source output terminals of
the IC. The gate–source voltage is a Pulse Width Modulated
(PWM) waveform having a variable ON/OFF duty cycle ratio
which is determined by an analog or a digital duty cycle
control circuitry which responds to variations in the system
voltage due to variations in system load current. The PWM
waveform has a duty cycle regulation output frequency of
about 395 Hz (fdc) defined by an 8 bit division of an internal
101 kHz oscillator clock frequency (fosc). The Gate voltage at
the Gate pin is due to a charge pump gate voltage (Vg)
generated by voltage multiplication using an internal charge
pump voltage regulator. The high gate–source voltage
applied to the external MOSFET during the ON cycle of the
PWM waveform minimizes a low drain–to–source ON
resistance (Rds(ON)) and accociated drain–source voltage
Vd(SAT) to maximize the field current while minimizing the
associated power dissipation in the MOSFET.
A unique feature of the MC33099 is the combinational use
of analog and digital duty cycle controllers to provide a Load
Response Control (LRC) duty cycle function when rotor
frequency fph is less than frequency f2. A classic analog duty
cycle function is provided at the Gate output when frequency
fph is greater than frequency f2. During the LRC mode when
f1 < fph < f2, a sudden decrease in the system voltage due to
a sudden increase in system load current will cause the
analog duty cycle to rapidly increase to as great as 100%.
However, the LRC circuitry causes the digital duty cycle to
increase to 100% at a controlled predetermined LRC rate and
overrides the analog duty cycle. Thus the alternator response
time is decreased in the LRC mode, and prevents the
alternator from placing a sudden high torque load on the
automobile engine during this slow RPM mode. This can
occur when a high current accessory is switched on to the
12V system, producing a sudden drop in system voltage.
When frequency fph is greater than frequency f2, the slow
LRC response is not in effect and the analog duty cycle
controller controls the PWM voltage waveform applied to the
external MOSFET to regulate the system voltage. By
selectively coupling the LRC1 and LRC2 terminals to ground,
or leaving them open, the user can program four different
LRC rates (Rlrc1–Rlrc4) from 9.37 %/sec to 37.4 %/sec.
During an initial ignition ON and engine start up the LRC rate
is also in effect to minimize alternator torque loading on the
engine during start, even when a Wide Open Throttle (WOT)
condition (fph > f2) occurs.
An internal N–Channel MOSFET is provided on the IC to
directly drive lamp current as a fault indicator. The fault lamp
is connected between the low side of the ignition switch and
the Lamp Drain terminal of the IC. A fault is indicated during
an undervoltage battery condition when frequency fph is
greater than frequency f2, during an overvoltage battery
condition, and when frequency fph is less than frequency f1.
Frequency fph < f1 when an insufficient alternator output
voltage results, or a slow or non–rotating rotor occurs due to
a slipping or broken belt. An external Lamp Gate pin is also
provided for the internal lamp driver to allow the user to
override the internal IC fault logic and externally drive the
internal lamp drive MOSFET.
When a lose wire or battery terminal corrosion causes the
Remote voltage to decrease but is not a Remote Open
condition, the system voltage will increase, causing an
overvoltage Lamp fault indication, and is regulated at a
secondary value of about 18.5V.
During a system load dump condition, load dump
protection circuitry prevents gate–to–source drive to the
external MOSFET and to the internal lamp drive MOSFET.
This insures that neither the field current nor the lamp current
is activated during load dump conditions. A drain–to–gate
voltage clamp is also provided for the internal lamp driver for
further protection of this driver during load dump.
An ignition pin (IGN) is provided to activate the regulator
from the standby mode into a normal operating mode when
the ignition switch is ON and an ignition voltage (Vign) is
greater than a power up/down ignition threshold voltage
(VTign). When the ignition switch is OFF, voltage Vign is less
than voltage VTign, and the regulator is switched into a low
current standby mode, when frequency fph < f1. The IGN pin
can either be coupled to the low side of the ignition switch, or
to the low side of the lamp. When the IGN pin is connected to
the low side of the lamp, the lamp must be shunted by a
resistor to insure that ignition ON is sensed, even with an
OPEN lamp fault condition. When the lamp in ON, lamp
current is polled OFF periodically at an ignition polling
frequency in order for the IGN pin to periodically sense that
the ignition voltage is high even though the lamp is ON. An
ignition input pull–down current (Iign) is provided to pull
voltage Vign to ground when the IGN terminal is OPEN, or
terminated on a high resistance.
Two ground terminals are provided by the MC33099 to
separate sensitive analog circuit ground (AGND) from noisy
digital and high current ground (Gnd).
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