33899 datasheet(20/26 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33899

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Figure 13. OFF-State Fault Detection Diagram

In the full or half H-Bridge mode an open, short to ignition,

or short to GND latches the appropriate SPI fault bits until the

FLTCLR bit is set. Any additional faults that occur prior to

setting FLTCLR will be ignored.

Fault Detection During OFF State

Fault detection for both the high side and low side outputs

is done during the OFF state, when either the EN1 or EN2 pin

is a logic [1], by analyzing the states of both the high side and

low side outputs interacting to the external load. S1 is pulled

up internally via a high-impedance pull-up to VCC, while S0 is

pulled down internally to ground. In a normal load state, the

low-impedance (relative to the internal pull-ups/pull-downs)

will force both load connections to about 0.5 VCC. S1 is

compared with an internal reference of 0.75 VCC nominally,

while S0 is compared to an internal reference of 0.25VCC

nominally. Table 7 indicates what status the load will be in

based on the combination of the outputs of these two

comparators.

Once any of the above faults are indicated for a period of

time exceeding the OFF-state fault timer, the fault bit will be

latched into the SPI Fault register. The OFF-state fault timer

is started when either the EN1 or EN2 pin transitions from a

logic [1] to a logic [0] (both inputs previously logic [1]) or from

a logic [0] to a logic [1] (both inputs previously logic [0]). The

OFF-state filter time is substantially longer than the ON-state

to allow energy in the load to dissipate. False open state

faults may be set when the outputs are shut down and the

load current (reverse polarity only) takes more than the OFF-

state filter time to decay to zero. The microprocessor should

clear the open state fault SPI bit and read the Fault register

again under this condition.

0.75 VCC

EN2

0.25 VCC

VCC

SGFON

SBFON

Fault

Timer

SGF

SBF

EN1

12 k

Note SGFON and SBFON are ON-State Fault.

Table 7. OFF-State Fault Detection

Load Status

<0.75 VCC

>0.25 VCC

Normal Load

<0.75 VCC

<0.25 VCC

Short to Ground

>0.75 VCC

<0.25 VCC

Open Load

>0.75 VCC

>0.25 VCC

Short to VIGNP

Load Current

(Reverse Polarity)

S0/S1 are at 2.5VDC,

No SPI Bits Set

Wake Up, Open

Fault Timer Starts

Open Fault

Timer Starts

Current in Load < 0, Erroneous

Open Fault SPI Bit Set

Goo Back

to Sleep

tFDO

EN1

EN2

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