L9374LF datasheet(42/80 Pages) STMICROELECTRONICS

42 / 80 page

Circuit description

L9374LF

42/80

DocID025414 Rev 1

Figure 26. Diagram under current

Figure 27. Diagram openload

4.8.2

Openload

Openload detection is done in the off-state through a multiplexed pull-down resistor, RPD

(see Figure 4). RPD is multiplexed onto each output node sequentially at a fixed 125kHz

rate. The output voltage is measured while RPD is connected to the output. Voltages below

VOL (Table 15) indicate an off-state Open load condition. Multiplexing RPD reduces the

overall “leakage” current while providing a substantial pull-down current to verify open load

status. There is a counter that “debounces” the open load detection similar to the

undercurrent filter counter. Open load is reported in the SPI status registers (bit D0 of

registers 1 - 4, 5.2.2: Output status Q1... Q4 (address 1 to 4)) and is cleared once read.

4.8.3

Overload

If the measured load current is higher than the overcurrent threshold (IOCx, Table 15) a

failure is detected. The overcurrent detection is measured in on state only. This failure is

filtered for tOL (20μs typ., Table 18). After tOL the output is shut down immediately and all of

the set point and control variables are set to zero. This disables the output from further

actuation until the appropriate status registers are read and cleared (refer to 5.2.2). Once

the appropriate SPI status registers are read the offending output(s) are released to be

driven again. This failure detection is used for all outputs.

The overcurrent bit is latched upon an overcurrent detection and reset after reading the

corresponding SPI register.

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