ATS344 datasheet(11/36 Pages) ALLEGRO

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High-Precision Linear Hall-Effect Sensor IC with Two-Wire

Current-Mode PWM Output and an Integrated Rare-Earth Pellet Package

ATS344

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

The programmable parameters determine the output temperature

compensation, YTC, according to the following formula:

YTC (%FSO) = YAD (%FSO)

+ [(TC1SENS (m%/°C) × ΔTA (°C)+

(TC2SENS (m%/°C2) × ΔTA (°C)2]

× YAD (%FSO)

+ TC1_OFFSET (G/°C)

× ΔTA (°C)

(1)

where:

YAD is the input from the analog subsystem via the A-to-D

converter;

TC1SENS is the first-order Sensitivity temperature coefficient, set

by either TC1_SENS_HOT, or TC1_SENS_CLD depending on

TA;

TC2SENS is the second-order Sensitivity temperature coefficient,

set by either TC2_SENS_HOT, or TC2_SENS_CLD depending

on TA;

TC1_OFFSET is the first-order Offset temperature coefficient (to

convert units from G/°C, divide the value by SensInit);

ΔTA is the change in ambient temperature from 25°C (for exam-

ple: at 150°C, ΔTA = 150°C – 25°C = 125°C, or at –40°C,

ΔTA = –40°C – 25°C = –65°C).

FINAL SENSITIVITY (GAIN) ADJUSTMENT

The ATS344 has a programmable parameter to adjust Sensitiv-

ity, SENSDC. The programmable parameter SENSDC, is used in

block 6 of Figure 4, for a fine adjustment of the Sensitivity. The

value of this 12-bit parameter, applied in the digital subsystem,

is multiplied to the factory Sensitivity value (see equation 3). For

example, SENSDC = 0 has a multiplier value of 4, SENSDC =

2047 has multiplier value of 8, and SENSDC = 2048 has a multi-

plier value of approximately 0. Refer to the EEPROM Customer-

Programmable Parameter Reference section for more information

on parameter SENSDC.

OUTPUT OFFSET FINE ADJUSTMENT

The ATS344 DSP subsystem also includes a parameter to adjust

the Quiescent Output, or offset. It is adjusted by the parameter

QVODC that controls the QOUT_FINE value. This program-

mable parameter, QVODC, is used as a fine adjustment to the

Quiescent Output and determines the value for QOUT_FINE, 6

in Figure 4. The value of QVODC is a percentage of the FSO.

It is programmable to add or subtract as much as 50% of FSO.

Refer to the EEPROM Customer-Programmable Parameter

Reference section for more information on parameter QVODC.

The QVODC parameter is programmed in the factory, in order to

be calibrated to a reference target. The customer should reference

and adjust this value.

The output of the digital subsystem, YDA, after applying the

parameters for f ine adjustment of Sensitivity and offset is shown

in equation 3. This value is prior to the clamps.

YDA (%FSO) = SENS_MULT × YTC (%FSO)

+ QOUT_F INE (%FSO)

(2)

Sens (%FSO/G) = SENSDC

× Factory Sensitivity

(3)

where SENS_MULT is the multiplication factor from 0 to 8 set

by the parameter SENSDC. The initial Sensitivity, Sensinit, is

defined with a SENS_MULT default of 4.

OUTPUT POLARITY SETTING

The OUTPUT_INVERT parameter sets the device output signal

polarity with respect to the sensed magnetic response polarity.

The default (0) is depicted in Figure 3, referenced to Figure 2,

where the sensor is moving relative to the target. Setting the

parameter to 1 inverts the output value.

OUTPUT CLAMPS SETTING

The ATS344 digital subsystem contains programmable clamp

features, to adjust the normal operating output range; see 8 in

Figure 4. The ATS344 output clamps are initially set to 0%

and 100% of FSO, for low and high output clamp respectively.

The programmable EEPROM parameters, CLAMP_HIGH and

CLAMP_LOW are available to adjust limits for the normal

operating output. The ATS344 Diagnostic outputs levels are not

bound by these parameters.

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