Hall Input Short-to-Battery Condition

The MAX9621 interprets a short to battery when the volt-

age at IN1 or IN2 is higher than VBAT - 100mV. The digital

outputs go low and the analog outputs are set to zero

output current. If IN1 or IN2 is more than 1V above VBAT,

it back-drives current into BAT. The MAX9621 restarts the

Hall inputs when the Hall input is loaded again.

Hall Input Short to Ground

The Hall input short-to-ground fault is effectively a latched

condition if the input remains loaded by the Hall switch.

The current required to power the Hall switch is shut off

and only a 50μA pullup current remains. The Hall input

can be manually reenergized or it can be reenergized by

the μP. A 10μs to 20μs negative pulse at SLEEP restarts

with a blanking cycle any Hall input that has been shut

down due to the short-to-ground condition. During startup

or restart, it is possible for a Hall input to charge up an

external capacitance of 0.02μF without tripping into a

short-to-ground latched state. During the short-to-ground

fault, DOUT1 and DOUT2 are high impedance (pulled

high by the pullup resistors), while AOUT1 and AOUT2

are set to zero-output current.

Manual Method for Reenergizing Hall

Sensor and Means for Diagnosing an

Intermittent Hall Sensor Connection

Figure 3 shows the behavior of the MAX9621 when a

Hall input is open. Figure 4 shows the behavior of the

MAX9621 when the open input is reconnected to a Hall

sensor. Figures 3 and 4 demonstrate how a short-to-

ground Hall input can be reset. Resetting a short-to-

ground Hall input involves three steps:

1) Relieve the short to ground at the Hall sensor.

2) Disconnect the Hall input from the Hall sensor (open-

input fault condition).

3) Reconnect the Hall input to the Hall sensor.

The MAX9621 restarts the Hall input with a blanking

cycle. If the Hall input is disconnected from the Hall sen-

sor for 10ms, it allows the Hall input to be pulled up by

the 50µA pullup current to register the open-input fault

condition. Reconnecting the Hall input to the Hall sensor

restarts the Hall input with a blanking cycle. This provides

a manual means of reenergizing a Hall input without hav-

ing to resort to the µP to restart it. This also demonstrates

the behavior of an intermittent connection to a Hall sensor.

Figure 3. Hall Input Ramps to Open-Circuit Fault When a Short to Ground Is Relieved

Table 1. AOUT_/DOUT_ Truth Table

*If IN_ is already shorted to BAT or open during power-up,

DOUT_ goes to high-Z until IN_ is loaded.

CONDITION

AOUT_

DOUT_

IN_ Short to GND

0

High-Z

IN_ Short to BAT or IN_ Open

0

Low*

SLEEP

Low

0

High-Z

VBAT > 18V

0

Low*

14V

VIN_

VBAT - 25mV

HALL INPUT

OPEN-CIRCUIT

FAULT

5mV/ms

IIN_

50µA

0V

0A

TIME

TIME

HALL INPUT

SHORT-TO-

GROUND FAULT

HALL INPUT

DISCONNECTED

FROM SENSOR

MAX9621

Dual, 2-Wire Hall-Effect Sensor Interface

with Analog and Digital Outputs

www.maximintegrated.com

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