33899 datasheet(21/26 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33899

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Fault Detection During ON State

While the H-Bridge circuit is in operation (i.e., when a high

side MOSFET is ON), the 33899 is capable of detecting both

shorts to VIGNP and shorts to ground. A short will cause the

appropriate MOSFETs to current limit. The current limit is

active for numerous retry periods until an over-temperature

condition is reached, at which time all outputs are turned

OFF.

All ON-state faults must be present for a period of time that

exceeds the fault time before the 33899 will consider them

valid. Once they are valid, they are latched until the SPI has

reported these faults to the microcontroller via the DO pin and

a logic [1] is written to the FLTCLR bit.

In order for the user to be certain that all detectable ON-

state faults have been reported, a minimum ON time is

required for the low side MOSFET. For example, if the PWM

frequency is 11kHz, ON-state fault detection would not be

guaranteed for duty cycles of less than 11%.

Thermal Shutdown

The H-Bridge has thermal protection circuitry. A thermal

fault sets the thermal shutdown bits (and any other faults that

may be present at that time) and latches off. The H-Bridge will

remain disabled until the microprocessor sets the FLTCLR bit

(refer to Table 8, page 22).

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