L9662 datasheet(33/80 Pages) STMICROELECTRONICS

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L9662

Functional description

Note:

SPI MISO sent in the next SPI transmission.

The device can only deploy a channel when the FEN function is active. Once the drivers are

active the device shall keep the drivers on for the required duration regardless of the FEN

state. Once completed, a status bit will be set to indicate firing is complete.

3.4.2

Firing current measurement

All channels have a 7 bit current measurement register that is used to measure the amount

of time the current is above IMEAS during firing. The maximum measurement for each

channel is 3.175 ms nominal based on a bit weight of 25 ms. The current measurement

begin incrementing once the current has exceeded 95% of the nominal target value. The

count will continue to increment from the stored value until either a clear command has

been issued for that channel or all ‘1’s are present in the corresponding channel

measurement register. If all ‘1’s are present for a channel’s measurement register and

another firing sequence has been issued the register shall remain all ‘1’s. Only if a clear

command has been issued will that particular register be reset to all ‘0’s. All other channels

shall keep the stored measurement count. During firing the current measurement register

cannot be cleared. After a clear command has been issued for a channel then the channel is

ready to count if the current exceeds the specified level. After a POR or software reset the

device shall reset all 8 measurement registers to all ‘0’s.

A “real-time” current measurement status of all the channels is available. If a current limit

status request is sent then the device shall report in the next SPI transfer whether the

current is above or below IMEAS for each of the channels. The current status results can be

read at any time and shall correctly report whether current is flowing. The content of the

internal current status register is captured on the falling edge of chip select during the SPI

response. The internal status register is updated at a nominal sample time of 25 μs and is

independent of SPI transfers.

For this circuit there is continuously being performed compensation of the comparator to

remove offset errors, which is independent from SPI commands. Compensation is

performed every 12.8 μs based on the internal clock.

3.4.3

Fire enable (FEN) function description

The Fire Enable (FEN) function is the result of the FENx input OR’d with the internal FEN

latch. If the FEN latch is not enabled and the FENx pin is low then activation of the FET

drivers are disabled except as indicated during the MOS test. All internal diagnostic

Table 11. SPI1 MOSI/MISO response

SPI1 MOSI

SPI1 MISO

Response

Configuration

Commands

SPI fault response

MOSI register mode messages shall be ignored

Deployment Commands Command mode

Execute for channels not in deployment; no effect

to deploying channel

Diagnostic Commands

SPI fault response

MOSI diagnostic mode messages shall be

ignored

Monitor Commands

Status response

Execute for all channels

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