Rainbow-electronics MAX9921 Bedienungsanleitung PDF herunterladen (Seite 11)

MAX9921

Dual, 2-Wire Hall-Effect Sensor Interface

with Diagnostics

______________________________________________________________________________________ 11

Hall Sensor Protection from Supply Transients

If the V

BAT

voltage is lower than 6V or exceeds 18V,

IN1 and IN2 shut off current to both Hall sensors and

ERR, OUT1, and OUT2 go low. When V

BAT

returns to

the proper range, both IN1 and IN2 restart, following a

blanking cycle.

Hall Inputs Open Condition

If either IN1 or IN2 is open (I

< 2mA), the correspond-

ing input shuts off current to the Hall sensor. If IN1 or

IN2 is loaded, it exits the open input fault condition and

restarts the corresponding Hall input, following a blank-

ing cycle.

Hall Input Shorted to Battery

If either IN1 or IN2 is shorted to the battery (V

> V

BAT

+ 100mV), the MAX9921 shuts off current to the corre-

sponding Hall sensor. In this case, if IN1 or IN2 is more

than 1V above V

BAT

, it may back-drive current into

BAT. In such a condition, the current level in the Hall

input should not exceed 100mA. Therefore, all the

MAX9921s together can share a separate reverse-

polarity protection diode to avoid powering up other cir-

cuitry sharing a common diode (Figure 4).

INPUT OUTPUT

DIAG ERR OUT1 OUT2

DIAGNOSIS

1 0 0 0 No fault

1 0 0 1 IN1 open circuit, or IN1 open circuit and fault on IN2

1 0 1 0 IN1 shorted to battery, or IN1 shorted to battery and fault on IN2

1 0 1 1 IN1 shorted to ground, or IN1 shorted to ground and fault on IN2

1100

BAT

out of range, or power-up or restart and blanking cycle (dominant

fault masks all other faults)

1 1 0 1 IN2 open circuit

1 1 1 0 IN2 shorted to battery

1 1 1 1 IN2 shorted to ground

Table 2. Diagnostic Truth Table (Diagnostic Mode)

BAT

ISET

MAX9921

IN1

IN2

GND

DIAG

ERR

OUT1

OUT2

BAT

GND

OTHER

CIRCUITRY

ISET

BATTERY

REVERSE-POLARITY DIODE

FOR MAX9921s

REVERSE-POLARITY DIODE

FOR OTHER CIRCUITRY

ISET

MAX9921

IN1

IN2

GND

DIAG

ERR

OUT1

OUT2

Figure 4. Several MAX9921s Connected to a Common Reverse-Polarity Diode

1 2 ... 6 7 8 9 10 11 12 13 14 15

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