ZSSC3008

Sensor Signal Conditioner with Diagnostics

Data Sheet

June 14, 2011

© 2011 Zentrum Mikroelektronik Dresden AG — Rev. 1.11

All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without

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Table 2.3

Summary of Diagnostic Features

Detected Fault

Analog

Diagnostic Level

ZACwire

Delay in Detection

EEPROM signature

Lower

Generates parity error

10ms after power-on

Loss of bridge positive

Upper

Generates parity error

2ms

Loss of bridge negative

Upper

Generates parity error

2ms

Open bridge connection

Upper

Generates parity error

2ms

Bridge input short

Upper

Generates parity error

2ms

Loss of VDD

Lower

Transmissions stop

Loss of VSS

Upper

Transmissions stop

2.6.1.

EEPROM Integrity

The contents of the EEPROM are protected by an 8-bit LFSR signature (linear feedback shift register). This sig-

nature is regenerated and stored in EEPROM every time EEPROM contents are changed. This signature is gen-

erated and checked for a match after Power-On-Reset prior to entering Normal Operation Mode. If the generated

signature fails to match, the part will output a diagnostic state on the output.

In addition to an extensive temporal and code interlock mechanism used to prevent false writes to the EEPROM,

the ZSSC3008 offers an EEPROM lock mechanism for high-security applications. When EEPROM bits 105:103

are programmed with “011” or “110,” this 3-bit field will permanently disable the VPP charge pump and will not

allow further writes to the EEPROM. See Table 2.3 in section 2.6 for more information.

2.6.2.

Sensor Connection Check

Four dedicated comparators permanently check the range of the bridge inputs (BP/BN) to ensure they are within

the envelope of 0.8V to 0.85

VDD during all conversions. The two sensor inputs have a switched ohmic path to

ground and if left floating, would be discharged. If any of the wires connecting the bridge break, this mechanism

will detect it and put the ASIC in a diagnostic state. This same diagnostic feature can also detect a short between

BP/BN. See Table 2.3 in section 2.6 for more information.

2.6.3.

Sensor Short Check

If a short occurs between BP/BN (bridge inputs), it would normally produce an in-range output signal and there-

fore would not be detected as a fault. This diagnostic mode, if enabled, will deliberately look for such a short. After

the measurement cycle of the bridge, it will deliberately pull the BP bridge input to ground for 4

sec. At the end of

this 4

sec window, it will check to see if the BN input “followed” it down below the 0.8V comparator checkpoint. If

so, a short must exist between BP/BN, and the part will output a diagnostic state. The bridge will have a minimum

of 480

sec recovery time prior to the next measurement. See Table 2.3 in section 2.6 for more information.