Dual, 2-Wire Hall-Effect Sensor Interface

with Diagnostics

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11

Hall Sensor Protection from Supply Transients

If the VBAT 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 VBAT 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 (IIN < 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 (VIN > VBAT

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

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

than 1V above VBAT, 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 3).

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

11

0

0

VBAT 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

OE

ERR

OUT1

OUT2

BAT

BAT

GND

OTHER

CIRCUITRY

RISET

BATTERY

REVERSE-POLARITY DIODE

FOR MAX9921s

REVERSE-POLARITY DIODE

FOR OTHER CIRCUITRY

RISET

ISET

MAX9921

IN1

IN2

GND

DIAG

OE

ERR

OUT1

OUT2

Figure 3. Several MAX9921s Connected to a Common Reverse-Polarity Diode