Hi,
The L9945 driver used in our proprietary automobile controller unit responsible for controlling actuators and pumps in exhaust system regulating harmful exhaust gases adhering to emission control policy.
Case1: OUT 2 channel:
Nominal frequency = 800 Hz, Max = 1000Hz
Short to Battery (STB)
• Function is consistent till 99.99% and no failure detected till the range.
• However, setting the frequency to maximum requirement 1000Hz caused failure even at 80% TON itself.
Short to Ground (STG)
• Failing after 98% with nominal frequency – no STG detection, detecting as open load
Open Load (OL)
• Failing after 98% with nominal frequency – no OL detection.
SPI command for channel 2: 0x26000082
Case 2: OUT 3 & OUT 7 channels: Both channels are configured as individual low side with same parameters
Nominal frequency = 10 Hz
Short to Battery (STB)
• Function is consistent till 99.97% and failure at 99.98%.
Findings!
• As per the configuration TDIAG_CONFIG_07, TOFF minimum threshold was set to 150µs. How ever, the driver already detected fault till TOFF 30µs even though threshold set to 150µs. Why and how?
Short to Ground (STG)
• Failing after 85% of TON itself with nominal frequency – no STG detection, detecting as open load
Open Load (OL)
• Failing after 85% of TON itself with nominal frequency – no OL detection.
SPI command for channel 7: 0x72C38082
SPI command for channel 3: 0x32C38083
I also checked "Criteria for configuring L9945 diagnostic parameters in automotive switching applications", states TDIAG < PWM OFF time. The least PWM OFF or TOFF time is 20µs when the duty cycle is set to 99.98% for 10Hz frequency (achieved in STB only). However, the scenario is different with STG and OL in both cases, the driver is failing consistently and sometime even at lesser duty cycle %. Please provide me any test or debug method to make the driver work at maximum efficiency.
