33810 datasheet(22/37 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33810

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

• Max dwell time

Soft Shutdown is designed to prevent an ignition spark

while turning off the external IGBT. The Low-voltage Clamp

is activated to provide the mechanism for a soft shutdown.

GAIN SELECT BIT

The ignition coil current comparators are used to compare

the programmed NOMI and MAXI DAC value with voltage

across the external current sense resistor. When selecting a

gain of two, the ignition coil current sense resistor must be

reduced from 40m

Ω to 20mΩ.

OVERLAPPING DWELL ENABLE BIT

Overlapping dwell occurs when two or more ignition mode

drivers are commanded ON at the same time. In this

condition, with the Overlapping Dwell Bit enabled the MAXI

DAC threshold value is increased as a percentage of the

nominal programmed value. The percent increase is

determined by bit 5 through bit 7 of the DAC Command.

Table 9. Overlapping Dwell Compensation

DAC Command

Bits<b7,b6,b5>

Overlap Compensation

(%)

000

001

010

15%

011

24%

100

35% (default)

101

47%

110

63%

111

80%

MAXIMUM DWELL ENABLE BIT

Bit 8, the Maximum Dwell Enable bit allows the user to

enable the Maximum Dwell Gate Turnoff Feature. When the

Max Dwell bit is programmed as logic 0 (disabled) the device

will not perform a Low-voltage Clamp due to Max Dwell (See

Figure 9).

MAXIMUM DWELL GATE TURN OFF FEATURE

In automotive ignition systems, dwell time is defined as the

duration of time that an ignition coil is allowed to charge. The

MC33810 starts the measure of time from the gate drive ON

command. If the dwell time is greater than the Max Dwell

Timer setting (Table 10), the offending ignition gate driver is

commanded OFF. The Max Dwell Gate Turn Off Feature may

be disabled via bit 8 of the Spark Command. When the

feature is disabled, the Max Dwell fault bits are always logic

0. The Max Dwell Timer feature pertains to Ignition Mode only

and does not affect gate drivers configured as general

purpose gate drivers.

The Max Dwell gate turn off signal is a logically ANDed

with the Soft Shutdown bit to activate a Low-voltage Active

Clamp (See Figure 9).

Table 10. Maximum Dwell Timer

Spark Command

Bit<b11,b10,b9>

MAX Dwell Timer

MaxDwell (ms)

000

001

010

011

100

32 (default)

101

110

111

DAC COMMAND (DIGITAL TO ANALOG

CONVERSION COMMAND)

The DAC Command is an ignition mode command that

sets the nominal ignition coil current (NOMI) and maximum

ignition coil current (MAXI) DAC values. Bits 0 through 4 set

the NOMI threshold value and, bits 8 through 11 set the MAXI

threshold values. The DAC command and default values are

listed in the SPI Command Summary Table 20. The NOMI

output is used by the MCU as a variable in dwell and spark

control algorithms.

NOMI DAC BITS

The NOMI output signal is generated by comparing the

external current sense resistor differential voltage (Resistor

Sense Positive, Resistor Sense Negative) with the SPI

programmed NOMI DAC value. When the NOMI event

occurs, the NOMI output pin is asserted (High). The NOMI

output is only a flag to the MCU and it’s output does not affect

the gate driver.

When using a 20 mΩ resistor as the current sense resistor,

the gain select of the differential amplifier connected to RSP

and RSN, should be set to a gain of 2, via the SPI Command

Message Spark Command (Command 0100, hex 4), Control

bit 6 =1.

When using a 40m

Ω resistor as the current sense resistor,

the gain select of the differential amplifier connected to RSP

and RSN, should be set to a gain of 1, via the SPI Command

Message Spark Command (Command 0100, hex 4), Control

bit 6 =0. This is also the default value.

The NOMI output provides a means to alert the MCU when

the ignition coil primary current equals the value programmed

into the NOMI DAC.

In V10 Mode, the NOMI pin is reconfigured as a MAXI

input pin from a third MC33810 device in the system. In this

mode a NOMI input has effectively the same control as an

internal MAXI signal. Further information is provided in the

V10 Mode application section of this data sheet.

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