33899 datasheet(13/26 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33899

FUNCTIONAL DESCRIPTION

FUNCTIONAL PIN DESCRIPTION

ENABLE INPUTS (EN1, EN2)

Logic [0] in either of the Enables (EN1 or EN2) disables all

four of the output drivers (refer to Table 6). While either EN1

or EN2 is at logic [1], the 33899 is still capable of detecting

open circuit and short circuit faults on all of the outputs

interfacing with the external load(s). The EN1 and EN2 inputs

have 50

μA pull-downs to ground that disable the outputs

when open circuit conditions occur.

Table 6. Enable Truth Table

INPUT CONTROL OF H-BRIDGE (PWM)

The PWM input pin controls the sequencing of the

PWM’ing high side and low side MOSFETs. A logic [1]

commands the appropriate low side MOSFET (M2 or M4) ON

and the appropriate high side MOSFET (M1 or M3) OFF. A

logic [0] commands the appropriate low side MOSFETs (M2

or M4) OFF and the appropriate high side MOSFETs (M1 or

M3) ON. The high and low side MOSFETs that are PWM’ed

are determined by the commanded direction (FWD or REV).

If a shorted condition exists, the particular output MOSFET

will be latched off after 5.0

μs to 10 μs. Subsequent PWM

edges will retry to turn on the same MOSFET. Only when a

thermal fault is reached are all outputs latched off until the

clear fault bit is set by the microprocessor. Any PWM high to

low to high pulse that is shorter than 500ns keeps the low-

side MOSFET from starting to turn off. The rising edge of this

short pulse re-enables the low side MOSFET if the pulse

width is at least 200

μs long (if a short circuit latch-off had

occurred during the previous positive PWM pulse). The PWM

input has a 50

μA pull-down to ground that disables all the

outputs should an open circuit condition occur.

Figure 7. 33899 Operation in Current Reversal

EN1

EN2

Status

Disabled (Sleep Mode)

Disabled (Standby Mode)

Enabled (Run Mode)

Forward Current

Reverse Current

Current in Load

reverses polarity

Both High Side

FET’s ON until

next PWM Rising

Edge

Load Current

Low Side FET

Body Diode

High Side FET

Body Diode

PWM

FWD

REV

33899 Datasheet(PDF) 13 Page - Freescale Semiconductor, Inc

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