Dual, 2-Wire Hall-Effect Sensor Interface

with Diagnostics

______________________________________________________________________________________

13

14V

VIN_

IIN_

0V

VBAT - 500mV

8V

4mA/

µs

11.5mA

0A

TIME

TIME

HALL INPUT

RECONNECTED

TO HALL SENSOR

Figure 5. Hall Input Re-Energized When Open Input is Reconnected to Hall Sensor

MAX9921 ACTIONS

FAULT

DESCRIPTION

CRITERION

ERR

OUTPUT

HALL INPUT RESPONSE

COMMENT/RECOVERY

VBAT < 6V

—

Asserted low

Shutoff current to both Hall

sensors

Both IN1 and IN2 are restarted with blanking

cycle when VBAT returns to proper range.

VBAT > 18V

—

Asserted low

Shutoff current to both Hall

sensors

Both IN1 and IN2 are restarted with blanking

cycle when VBAT returns to proper range.

Hall input open

IIN < 2mA

Asserted low

Shutoff current to

corresponding Hall sensor

When a Hall input is again loaded, terminating

open input condition, the Hall input are restarted

with blanking cycle.

Hall input shorted

to battery

VIN > VBAT due

to external

reverse-battery

protection

diode

Asserted low

Shutoff current to

corresponding Hall sensor

If a Hall input is pulled more than 1V above

VBAT, the input may back drive current into the

BAT supply and pull VBAT up with it. In this

condition, current levels in the Hall inputs should

never exceed 100mA. For this reason, it is

recommended that one or more MAX9921s be

powered together and share a reverse-polarity

diode separate from other circuitry.

Hall input shorted

to ground

IIN > 23mA

Asserted low

Shutoff current to

corresponding Hall sensor.

50µA of pullup current is

sourced to IN1 or IN2 to

aid in troubleshooting.

A falling edge at DIAG initiates a restart with a

blanking cycle of any Hall input that has been

shut off due to a short to ground. See the Hall

Input Short-to-Ground section.

Table 3. Summary of Fault Protection and Recovery