MAX1454_11 Datasheet, PDF(10/25 Page) Maxim Integrated Products – Precision Sensor Signal Conditioner with Overvoltage Protection

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MAX1454

Precision Sensor Signal Conditioner

with Overvoltage Protection

This index determines which FSO and offset DAC

settings get loaded from the flash memory. The

temperature-indexing boundaries are outside of the

specified Absolute Maximum Ratings to eliminate index-

ing wrap-around errors. The minimum indexing value

is 0x00, corresponding to approximately -82NC. All

temperatures below this value generate the index 0x00.

The maximum indexing value is 0xAF, corresponding

to approximately +185NC. All temperatures higher than

+185NC generate the index 0xAF.

Overvoltage, Undervoltage,

Reverse-Voltage Protection

Overvoltage protection shuts down the device when the

supply voltage is typically above 5.75V. A power-on reset

prevents erroneous operation with supply voltages below

2.4V. Reverse voltage protects the device from negative

voltages due to transients, reverse battery, etc. These

protections allow the device to withstand any supply volt-

age from -45V to +45V.

Sensor Fault Detection

When enabled, the fault-detection circuitry on the device

detects faults on the sensor inputs (IN+ and IN-). If either

one of the sensor inputs is below the input low threshold

(20% of VBDR) or above the input high threshold (80% of

VBDR), a fault signal is asserted internally. If the part is in

analog mode, the internal fault signal causes the voltage

on the OUT/DIO pin to clip to a fixed DC level (typically

150mV). Enable or disable fault detection through the

CONFIG2 register, bit 6 (ENFDET).

Internal Calibration Registers (ICRs)

The device has six 16-bit ICRs (ODAC, FSODAC,

OTCDAC, FSOTCDAC, CONFIG1, and CONFIG2) that

are loaded from flash memory, or loaded from the serial

digital interface when in the digital programming mode.

Data can be loaded into the ICRs under two different

modes of operations (fixed analog operation and calibra-

tion operation).

Fixed Analog Operation

U The device has been calibrated.

U Power is applied to the device.

U The power-on-reset functions have completed.

U The digital listening mode times out and the device

goes into the fixed analog mode.

U The internal temperature sensor stores the 8-bit

TEMPINDEX value.

U Registers CONFIG1, CONFIG2, ODAC, FSODAC,

OTCDAC, and FSOTCDAC are loaded from flash

memory.

U After each time the DAC refresh timer reaches its set

time period, the internal-temperature ADC updates the

8-bit TEMPINDEX value and the ODAC and FSODAC

registers are refreshed from the temperature-indexed

flash memory locations.

Calibration Operation

(Registers Updated by Serial Communications)

U Power is applied to the device.

U The power-on-reset functions have completed.

U The digital listening mode detects serial communication.

U The registers can then be loaded from the serial

digital interface by use of serial commands. See the

Serial-Interface Command Format section.

U (Optionally) After calibration, the device can be set to

run in fixed analog operation using a software com-

mand. Note that the configuration and DAC registers

refresh from flash memory upon entering fixed analog

mode.

Internal Flash Memory

The internal flash memory is organized as a 2K by 8-bit

memory. It is divided into four pages with 512 bytes

per page. Each page can be individually erased. The

memory structure is arranged as shown in Table 1. The

lookup tables for ODAC and FSODAC are also shown,

with the respective TEMPINDEX pointer. The ODAC table

occupies a segment from address 0x000 to address

0x15F, and the FSODAC table occupies a segment from

0x200 to 0x35F.

The flash memory is configured as an 8-bit wide array so

each of the 16-bit registers is stored as two 8-bit quanti-

ties. The configuration registers and the FSOTCDAC

and OTCDAC registers are loaded from the preassigned

locations in the flash memory. The ODAC and FSODAC

registers are loaded from memory lookup tables using an

index pointer that is a function of temperature.

Maxim programs all flash memory locations to 0xFF,

except for the reserved locations, 0x400 and 0x401.

Values stored at 0x400 and 0x401 should be kept at the

factory-programmed defaults.

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