MAX9921 Maxim Integrated Products, MAX9921 Datasheet - Page 14

• Manufacturer Part Number: MAX9921
• Description: 2-Wire Hall-Effect Sensor Interface
• Manufacturer: Maxim Integrated Products

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Table 4. Partial List of Compatible Hall Switches
Dual, 2-Wire Hall-Effect Sensor Interface
with Diagnostics
The MAX9921 is optimized for use with 2-wire Hall-
effect switches or with 3-wire Hall-effect switches con-
nected as 2-wire (Figure 7). When using a 3-wire Hall
sensor, the resistor R is chosen so that the current
drawn by the Hall sensor crosses the MAX9921 current
threshold when the magnetic threshold of the Hall sen-
sor is exceeded.
Table 4 shows a partial list of mostly 2-wire Hall switch-
es, which can be used with the MAX9921.
Figure 7. 3-Wire Hall-Effect Switches Configured as 2-Wire
14
HAL573-6
HAL556/560/566
HAL581/584
A1140/1/2/3
3161
TLE4941/C
______________________________________________________________________________________
x_
PART
V
CC
Applications Information
Hall-Effect Sensor Selection
R
MANUFACTURER
Micronas
Micronas
Micronas
Infineon
Allegro
Allegro
IN_
MAX9921
GND
www.micronas.com
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www.allegromicro.com
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WEBSITE
The MAX9921 is optimized for use with external protec-
tion 0.01µF capacitors from both IN1 and IN2 to BAT.
These are essential to ensure robustness against auto-
motive transients. These capacitors may be tied to
GND instead of to BAT, but the connection to BAT is
recommended.
To ensure correct operation of the Hall sensor at low
input voltages, it is important to consider the voltage
drop of the MAX9921 with low battery voltages. This
dropout voltage can be calculated using the formula:
I
the Hall sensor and R
MAX9921, nominally 50Ω (see the Input Pullup
Resistance vs. V
Characteristics ). As an example, assume the use of a
HAL573 sensor, which draws a maximum current of
17mA. The dropout voltage is then 850mV and the
approximate minimum voltage supplied to the Hall sensor
is 6V - 0.85V = 5.15V, which is higher than the minimum
operating voltage of 3.75V specified for the HAL573.
HALL
is the maximum current which must be supplied to
2-wire
2-wire
2-wire
2-wire
3-wire, optimized for 2-wire use without added
resistor
2-wire
V
DROPOUT
BAT
Hall Input Bypass Capacitor
PU
graph in the Typical Operating
is the internal resistance of the
Low-Voltage Operation
= I
HALL
COMMENT
x R
PU