Self-Calibrating TPOS Speed Sensor IC

Optimized for Automotive Cam Sensing Applications

ATS675LSE

11

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

AGC is activated during the Initial Calibration stage at each

power-on. The device measures the peak-to-peak application

magnetic gradient, and then the gain of the sensor IC is adjusted

date any input signal amplitude within the specified Operating

magnetic baseline. At the end of the Initial Calibration stage, the

AGC results are latched and they are not readjusted while the

device remains powered-on.

Power Supply Protection

The ATS675 provides features for protecting the device against

power supply aberrations:

Undervoltage Lockout When the supply voltage falls below

changes to Off. The device remains in that state until the volt-

target magnetic gradient have no effect until that voltage level

is restored. This prevents false signals caused by undervoltage

conditions from propagating to the output of the sensor IC.

EMC Protection The ATS675 contains an on-chip regulator

that operates throughout a wide range of supply voltage levels.

For applications using an unregulated power supply, protection

against transients may be added externally. For applications using

a regulated supply line, EMI and RFI protection may still be

required. Contact Allegro for information on EMC specification

compliance.

Operating Modes

The device provides three operating modes: TPOS, Calibration,

and Running. TPOS and Calibration initialize simultaneously at

power-on. TPOS generates immediate device output, controlling

device switching while the calibration functions are performed.

After calibration is complete, normal operation in Running mode

begins.

TPOS (True Power-On State) Operation

an output voltage corresponding to the target feature opposite the

device. It does so by comparing the existing level of the appli-

an internal threshold used to distinguish a tooth from a valley

during TPOS operation (from power-on until the end of the Initial

is evaluated as a tooth.

Calibration Mode Operation

At power-on (simultaneous with TPOS operation) Calibration

mode begins. Calibration mode is performed in two stages: the

Initial Calibration stage, followed immediately by the TPOS to

Running Mode Transition stage (see figure 7). After the second

calibration stage, Running mode begins immediately.

In Calibration mode, the operating range of the application

ATS675 electronics are adapted for optimal output switching.

Calibration is performed quickly, without reading the entire tar-

get, because the ATS675 applies the internal magnetic baseline.

Initial Calibration Stage During the Initial Calibration stage,

TPOS operation controls device output switching while calibra-

tion starts. In this stage, the peak-detecting DACs acquire the

application magnetic signal. Based on those results, the Auto-

matic Gain Control (AGC) feature calculates the normalized

Running mode switching range. This period is minimized, so

swapping to the Running mode thresholds can occur as quickly as

possible.

TPOS to Running Mode Transition Stage At the beginning

of this stage, TPOS operation terminates, and throughout this

stage the device automatically adjusts the output switching levels

from the original preset switching level to the Running mode

switchpoints. This transition takes place over one tooth, immedi-

ately swapping from TPOS to Running mode switchpoints.

Figure 7. Calibration mode waveforms.

Time

Running mode

switchpoints for

I option

TPOS switching

level

On

Output State

for HT option

Off

On

Off

On

Off

Running Mode