Analog Integrated Circuit Device Data

10

Freescale Semiconductor

33099

TYPICAL APPLICATIONS

Modulated (PWM) waveform having a variable ON/OFF duty

cycle ratio that is determined by an analog or a digital duty

cycle control circuitry that responds to variations in the

system voltage due to variations in system load current. The

PWM waveform has a duty cycle regulation output frequency

generated by voltage multiplication using an internal charge

pump voltage regulator. The high GATE-to-source voltage

applied to the external MOSFET during the ON cycle of the

PWM waveform minimizes a low drain-to-source ON

associated power dissipation in the MOSFET.

A unique feature of the 33099 is the combinational use of

analog and digital duty cycle controllers to provide a Load

Response Control (LRC) duty cycle function when rotor

cycle function is provided at the GATE output when

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 12

V system, producing a sudden drop in system voltage. When

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 pins to ground or leaving them

ON and engine start-up, the LRC rate is also in effect to

minimize alternator torque loading on the engine during start,

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 pin of the IC. A fault is indicated during an

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 loose wire or battery pin 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 18.5 V.

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 ensures 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

greater than a power up/down ignition threshold voltage

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 ensure 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

terminated on a high resistance.

Two ground pins are provided by the 33099 to separate

sensitive analog circuit ground (AGND) from noisy digital and

high-current ground (GND).

ALTERNATOR REGULATOR BIASING AND

POWER UP/DOWN

The biasing of the regulator is derived from the BAT pin

provides bias to a bandgap shunt voltage regulator. The

approximately 2.0 V with an internal negative temperature

coefficient (-TC) as well as a 1.25 V Zero Temperature

Coefficient (OTC) reference voltage. Additional bias currents

and reference voltages, including a charge pump GATE

mode, having a standby drain current of about 0.7 mA

voltage regulators and bias currents are either terminated or

addition, all logic is reset in the standby mode.

After switching the ignition switch to the ON position,

Ignition Delay circuit. After an Ignition start Delay Time of

500 ms, the Ignition Delay circuit activates additional current