L9908 datasheet(91/152 Pages) STMICROELECTRONICS

91 / 152 page

OFDn_EN1

OFDn_EN0

Description

Pull-up current enabled, pull-down current disabled

Pull-down current enabled, pull-up current disabled

Off-State diagnosis disabled

The OFD is automatically enabled when the OFD_EN bit is set and INLn/INHn = 0 [n = 1,2,3]. Once enabled, the

OFD circuit is stopped as soon as a 0 → 1 transition of INHn/INLn is detected.

Depending on the external load condition, the OFD configuration and detection shall follow the next table:

Table 85. OFD fault detection table

Condition

OFD_EN[1:0]

Error flag

Description

3-Phase OFD

[Three phase load]

OFD1 = 10

OFD2 = 01

OFD3 = 10

HS2_OFD = X(1)

LS1_OFD = 0

LS2_OFD = 0

LS3_OFD = 0

Short to ground on one or multiple motor phases

HS2_OFD = 0

LS1_OFD = 1

LS2_OFD = 1

LS3_OFD = 1

Short to battery on one or multiple motor phases

HS2_OFD = X(1)

LS1_OFD = 0

LS2_OFD = 1

LS3_OFD = 1

Open connection on motor phase 1 (SHS_1)

HS2_OFD = X(1)

LS1_OFD = 0

LS2_OFD = 1

LS3_OFD = 0

Open connection on motor phase 2 (SHS_2)

HS2_OFD = X(1)

LS1_OFD = 1

LS2_OFD = 1

LS3_OFD = 0

Open connection on motor phase 3 (SHS_3)

HS2_OFD = 1

LS1_OFD = 1

LS2_OFD = 1

LS3_OFD = 1

No fault

1. X = do not care.

Note:

•

The OFD circuit can detect a SCB or SCG condition affecting the three phases in general, due to the low

DC resistance of the motor it cannot identify at which phase the failure is present.

•

Correct functionality of OFD is based on a current mismatch between pull-up and pull-down current. In

case of additional external pull-up/down contribution the following inequation must be satisfied:

IPU_TOTx>IPD_TOT_PHy+IPD_TOT_PHz

(21)

Where:

Ipu_totx is the equivalent pull-up current injected into the phase x (assuming phase x being configured as

OFD_EN = 01)

Ipd_toty and Ipd_totz are the equivalent pull-down currents injected respectively into the phase y and z

(assuming phase y and z being configured as OFD_EN = 10)

L9908

Functional description

DS13546 - Rev 5

page 91/152

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