L9958 datasheet(23/38 Pages) STMICROELECTRONICS

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L9958

Diagnostics and protections

5.3

Off-state diagnosis

This diagnostic is performed in any off-state condition, just after ignition key-on or during an

off-state phase occurring after an on-state phase of the bridge.

5.3.1

Off-state detection scheme

In order to avoid any wrong diagnostic, a filtering time "Tdiag_off" is applied before

performing the detection if the bridge was in on-state before. This filtering time is not applied

in case of detection after key on.

Figure 18. Off-state detection scheme

5.3.2

Open load detection

An equivalent resistor of 100 k

 (typ.) is targeted for open-load detection.

In order to avoid any unwanted supply of the bridge through the high-side transistor body

diode during off-state measurement, the current source is connected only if Vs is higher

than the Vs under-voltage threshold.

Figure 19. Open load detection

The diagnostic is based on a closed loop voltage control on OUT1 and associated current

measurement.

A voltage amplifier forces a constant voltage on OUT1 through two current sources (high-

side source and low-side current sink). The OUT2 is pulled-down through a constant current

sink. Based on the current flowing out of the amplifier (Ip – In) compared to several current

thresholds, open-load as well as short-circuit to ground and battery can be detected.

L9958 Datasheet(PDF) 23 Page - STMicroelectronics