Single Element, Tooth Detecting Speed Sensor IC

ATS601

11

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Operating Modes

Startup Hysteresis Mode

After power-on, a minimum amount of peak-to-peak magnetic

movement is required before the ATS601 will begin generating

output edges. This required signal movement threshold is referred

to as the startup hysteresis. There are two programmable options

for this startup hysteresis threshold. With narrow (N option)

startup hysteresis, the device will switch to a farther air gap, but

will have reduced immunity to magnetic overshoot, thus limiting

its close air gap capability. With wide (W option) startup hyster-

esis, the device will have a reduced maximum air gap capability,

but improved magnetic overshoot immunity. After the magnetic

signal exceeds the startup hysteresis value for the first time, the

device will transition to Calibration mode.

Calibration Mode

In Calibration mode, the ATS601 uses threshold based switching

with continuous update. This ensures that all teeth and valleys

are captured correctly, but provides slightly reduced accuracy

relative to Running mode. The device stays in Calibration mode

long enough to correctly capture enough peaks to fill the Running

mode threshold memory. This corresponds to three output edges

with the single-tooth update (1 option) and nine edges with the

four-tooth update (4 option). After Calibration mode is complete,

the device transitions to Running mode.

Running Mode

In Running mode the ATS601 uses threshold based switching

with internal hysteresis described previously, in the Thresh-

old Update and Switchpoints sections. The threshold update is

intended to optimize output switching accuracy when used with

common camshaft targets, including cases with runout and nar-

row target valleys.

Stop Mode

The ATS601 has an internal timer that begins counting on each

occurs, the device moves into Stop mode. Stop mode is the same

as Startup Hysteresis mode, but with a hysteresis value

determined as a percentage of the previously measured target

amplitude. Stop mode ensures no missed or extra output

edges, even during situations with large temperature drifts and

no target rotation.

Watchdog

The ATS601 has a peak detector continuously tracking the mag-

netic signal. If a sudden large signal change causes the sensor IC

output to stop switching but the peak detector continues to detect

valid signal movement, the watchdog will be fired. In case of a

watchdog event, the sensor IC performs a self-reset and returns to

the initial Startup Hysteresis mode to regain output switching.