L9945 datasheet(128/144 Pages) STMICROELECTRONICS

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Table 46. Open Load output voltage

Symbol

Parameter

Min.

Typ.

Max.

Unit

VOUT_OL

Vout node voltage in case of open load

2.25

2.5

2.75

Note:

Vout corresponds to DRNx pin for LS NMOS and HS PMOS configurations, while it's SNGPx pin for HS NMOS

configuration.

Regulator current capability IDIAG can be programmed via diag_i_config_xx bit as follows:

Table 47. Vout regulator current capability IDIAG

diag_i_config_xx

Min.

Max.

Unit

100

µA

0.6

A higher current capability allows compensating the leakage of external devices (FET, recirculation diodes, etc.)

The current limitation feature allows distinguishing between OL and STB/STG faults:

•

In case of open load, the regulator is able to drive Vout around VOUT_OL and the OL fault is flagged;

•

In case of STB/STG fault, due to the limited current capability, the regulator has no effect on Vout.

Therefore, output node voltage stays below VLVT (STG on LS) or above VOL (STB on HS).

Refer to Figure 37 and Figure 39 for OL regulator operation in HS configuration.

Refer to Figure 38 and Figure 39 for OL regulator operation in LS configuration.

6.4.4

Fast charge/discharge currents

To reliably detect a fault, the Vout voltage must be stable before the settling time tDIAG expires.

In case of STB/STG faults, high current capability of battery and ground supplies guarantee fast Vout settling.

In case of open load, Vout must be brought in the [VLVT; VOL] range before tDIAG expires to guarantee fault

detection. The device implements internal fast charge/discharge currents to allow settling of Vout in a time suitable

for detection:

•

When the HS transistor is switched OFF, a fast discharge current IFAST_DIS rapidly decreases Vout down to

VOL to help the OL regulator detect an eventual open load fault (see Figure 37 and Figure 39). IFAST_DIS is

enabled in the case:

–

The HS channel has been just switched OFF;

–

The settling time tDIAG is still running;

–

Vout is above VOL.

•

When LS transistor is switched OFF, a fast charge current IFAST_CHG rapidly increases Vout up to VLVT to

help the OL regulator detect an eventual open load fault (see Figure 38 and Figure 39). IFAST_CHG is

enabled in the case:

–

The LS channel has been just switched OFF;

–

The settling time tDIAG is still running;

–

Vout is below VLVT.

L9945

Safety & diagnostics

DS12275 - Rev 10

page 128/144

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