33887 datasheet(23/37 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33887

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

The 33887 Simplified Internal Block Diagram shown in

Figure 2, page 2, is a fully protected monolithic H-Bridge with

Enable, Fault Status reporting, and High-Side current sense

feedback to accommodate closed-loop PWM control. For a

DC motor to run, the input conditions need be as follows:

Enable input logic HIGH, D1 input logic LOW, D2 input logic

HIGH, FS flag cleared (logic HIGH), one IN logic LOW and

the other IN logic HIGH (to define output polarity). The 33887

can execute dynamic braking by simultaneously turning on

either both high-side MOSFETs or both low-side MOSFETs

in the output H-Bridge; e.g., IN1 and IN2 logic HIGH or IN1

and IN2 logic LOW.

The 33887 outputs are capable of providing a continuous

DC load current of 5.0 A from a 28 V V+ source. An internal

charge pump supports PWM frequencies to 10 kHz. An

external pull-up resistor is required at the FS pin for fault

status reporting. The 33887 has an analog feedback (current

mirror) output pin (the FB pin) that provides a constant-

current source ratioed to the active high-side MOSFET. This

can be used to provide “real time” monitoring of load current

to facilitate closed-loop operation for motor speed/torque

control.

Two independent inputs (IN1 and IN2) provide control of

the two totem-pole half-bridge outputs. Two disable inputs

(D1 and D2) provide the means to force the H-Bridge outputs

to a high-impedance state (all H-Bridge switches OFF). An

EN pin controls an enable function that allows the 33887 to

be placed in a power-conserving sleep mode.

The 33887 has undervoltage shutdown with automatic

recovery, active current limiting, output short-circuit latch-

OFF, and overtemperature latch-OFF. An undervoltage

shutdown, output short-circuit latch-OFF, or overtemperature

latch-OFF fault condition will cause the outputs to turn OFF

(i.e., become high impedance or tri-stated) and the fault

output flag to be set LOW. Either of the Disable inputs or V+

must be “toggled” to clear the fault flag.

Active current limiting is accomplished by a constant OFF-

time PWM method employing active current limiting threshold

triggering. The active current limiting scheme is unique in that

it incorporates a junction temperature-dependent current limit

threshold. This means the active current limiting threshold is

“ramped down” as the junction temperature increases above

160

°C, until at 175°C the current will have been decreased to

about 4.0 A. Above 175

°C, the overtemperature shutdown

(latch-OFF) occurs. This combination of features allows the

device to remain in operation for 30 seconds at junction

temperatures above 150

°C for nonrepetitive unexpected

loads.

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