TPIC44L01, TPIC44L02, TPIC44L03

4CHANNEL SERIAL AND PARALLEL LOW SIDE PREFET DRIVER

14

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

open load

The TPIC44L01, TPIC44L02, and TPIC44L03 monitor the drain of each power FET for open circuit conditions

that may exist. The 60-

µA current source is provided to monitor open load fault conditions. Open-load faults are

only detected when the power FET is turned off. When load impedance is open or substantially high, the 60-

µA

current source has adequate drive to pull the drain of T1 below the fault reference threshold on the detection

reporting of open-load fault conditions. The onboard deglitch timer starts running when the TPIC44L01,

TPIC44L02, and TPIC44L03 gate output to the power FET transitions to the off state. The timer provides a 60-

µs

time is only enabled for the first 60

µs after the FET has been turned off. After the deglitch delay time, the drain

is checked to verify that it is greater than the fault reference voltage. When it is less than the reference voltage,

a fault is flagged to the microcontroller through FLT that an open-load fault condition exists. The microcontroller

can then read the serial port on the TPIC44L01, TPIC44L02, and TPIC44L03 to isolate which channel reported

the fault condition. Fault bits 0–3 distinguish faults for each of the output channels. Figure 15 illustrates the

operation of the open-load detection circuit. This feature provides useful information to the microcontroller to

isolate system failures and warn the operator that a problem exists. Examples of such applications would be

a warning that a light bulb filament may be open, solenoid coils may be open, etc.

NORMAL

_

+

N-Channel

Load

VBAT

T1

External

TPIC44L01/L02/L03

1.25 V

Deglitch

FLT

Input From

TPIC44L01/L02/L03

60

µA

U1

t(STBFM)

Glitches

Input

DRAIN0–

DRAIN3

FLT

OPEN-LOAD

NORMAL

GATE0–

GATE3

Input

DRAIN0–

DRAIN3

FLT

GATE0–

GATE3

t(STBFM)

Figure 15