MAX9921AUB+ Maxim Integrated Products, MAX9921AUB+ Datasheet - Page 12

• Manufacturer Part Number: MAX9921AUB+
• Description: IC SENSOR HALL EFFECT 10-MSOP
• Manufacturer: Maxim Integrated Products
• Type: Hall Effect Sensorr

Specifications of MAX9921AUB+

• Input Type: Voltage
• Output Type: Logic
• Interface: 2-Wire
• Current - Supply: 1.3mA
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The Hall input shorted-to-ground fault is effectively a
latched condition if the input remains loaded by the Hall
switch when the shorting condition is removed. The cur-
rent required to power the Hall switch is shut off and only
a 50µA pullup current remains. The Hall input can be
manually re-energized or it can be re-energized by the
ECU. A falling edge at DIAG initiates a restart with a
blanking cycle of any Hall input that has been shut down
due to the shorted-to-ground condition. During startup or
restart, it is possible for a Hall input to charge up an exter-
nal capacitance of 0.02µF without tripping into a shorted-
to-ground latched state. All other fault conditions are not
latched and when these other faults are removed, ERR
goes high and the Hall input is again functional.
Figure 4 shows the behavior of the MAX9921 when a
Hall input is open. Figure 5 shows the behavior of the
MAX9921 when the open input is reconnected to a Hall
sensor. Figures 4 and 5 demonstrate how a shorted-to-
ground Hall input can be reset.
Dual, 2-Wire Hall-Effect Sensor Interface
with Diagnostics
Figure 4. Hall Input Ramps to Open-Circuit Fault When Short to Ground is Relieved
12
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Manual Method for Re-Energizing Hall Sensor
V
I
IN_
IN_
50µA
and Means for Diagnosing an Intermittent
14V
0V
0A
DISCONNECTED
FROM SENSOR
HALL INPUT
Hall Input Short-to-Ground
GROUND FAULT
Hall Sensor Connection
HALL INPUT
INDICATED
SHORT TO
5mV/ms
HALL INPUT
OPEN-CIRCUIT
FAULT INDICATED
Resetting a shorted-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
3) Reconnect the Hall input to the Hall sensor.
The MAX9921 restarts the Hall input with a blanking
cycle. If the Hall input is disconnected from the Hall
sensor for 10ms, it allows the Hall input to be pulled up
by the 50µA pullup current to register the open-input
fault condition. Then, reconnecting the Hall input to the
Hall sensor restarts the Hall input with a blanking cycle.
This provides a manual means of re-energizing a Hall
input without having to resort to the ECU to reset it. This
also demonstrates that an intermittent connection to a
Hall sensor can recover without intervention of the ECU.
This gives the ECU a means of diagnosing an intermit-
tent connection to a Hall sensor by using the diagnostic
mode to detect a diagnostic sequence of “open-circuit”
to “blanking cycle” to “no fault.”
input fault condition).
V
BAT
- 25mV
TIME
TIME