MAX1455AAE-T Maxim Integrated Products, MAX1455AAE-T Datasheet - Page 9

• Manufacturer Part Number: MAX1455AAE-T
• Description: Board Mount Temperature Sensors Automotive Sensor Signal Conditioner
• Manufacturer: Maxim Integrated Products

Specifications of MAX1455AAE-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The internal EEPROM is organized as a 768 by 8-bit
memory. It is divided into 12 pages, with 64 bytes per
page. Each page can be individually erased. The memo-
ry structure is arranged as shown in Table 1. The look-up
tables for ODAC and FSODAC are also shown, with the
respective temperature index pointer. Note that the
ODAC table occupies a continuous segment, from
address 000hex to address 15Fhex, whereas the
FSODAC table is divided in two parts, from 200hex to
2FFhex, and from 1A0hex to 1FFhex. With the exception
of the general-purpose user bytes, all values are 16-bit-
wide words formed by two adjacent byte locations (high
byte and low byte).
The MAX1455 compensates for sensor offset, FSO, and
temperature errors by loading the internal calibration
registers with the compensation values. These com-
pensation values can be loaded to registers directly
through the serial digital interface during calibration or
loaded automatically from EEPROM at power-on. In this
way, the device can be tested and configured during cal-
ibration and test and the appropriate compensation val-
ues stored in internal EEPROM. The device autoloads the
registers from EEPROM and is ready for use without fur-
ther configuration after each power-up. The EEPROM is
configured as an 8-bit-wide array so each of the 16-bit
registers is stored as two 8-bit quantities. The
Configuration register, FSOTCDAC, and OTCDAC regis-
ters are loaded from the preassigned locations in the
EEPROM. Table 2 is the EEPROM ODAC and FSODAC
lookup table memory map.
The ODAC and FSODAC are loaded from the EEPROM
lookup tables using an index pointer that is a function
of temperature. An ADC converts the integrated tem-
perature sensor to an 8-bit value every 1ms. This digi-
tized value is then transferred into the Temp-Index
register. Table 3 lists the registers.
The typical transfer function for the temp-index is as fol-
lows:
where temp-index is truncated to an 8-bit integer value.
Typical values for the Temp-Index register are given in
Table 4.
Note that the EEPROM is 1 byte wide and the registers
that are loaded from EEPROM are 16 bits wide. Thus,
each index value points to 2 bytes in the EEPROM.
Maxim programs all EEPROM locations to FFhex with
the exception of the oscillator frequency setting and
Secure-Lock byte. OSC[2:0] is in the Configuration
register (Table 5). These bits should be maintained at
the factory-preset values. Programming 00hex in the
temp-index = 0.69
_______________________________________________________________________________________
✕
Temperature (°C) + 47.58
Internal EEPROM
Low-Cost Precision Sensor Signal
Secure-Lock byte (CL[7:0] = 00hex) configures the DIO
as an asynchronous serial input for calibration and test
purposes.
A single-pin serial interface provided by the DIO
accesses the MAX1455’s control functions and memo-
ry. All command inputs to this pin flow into a set of 16
registers, which form the interface register set (IRS).
Additional levels of command processing are provided
by control logic, which takes its inputs from the IRS. A
bidirectional 16-bit latch buffers data to and from the
16-bit Calibration registers and internal (8-bit-wide)
EEPROM locations. Figure 5 shows the relationship
between the various serial commands and the
MAX1455 internal architecture.
The DIO serial interface is used for asynchronous serial
data communications between the MAX1455 and a host
calibration test system or computer. The MAX1455 auto-
matically detects the baud rate of the host computer
when the host transmits the initialization sequence. Baud
rates between 4800 and 38400 can be detected and
used. The data format is always 1 start bit, 8 data bits,
and 1 stop bit. The 8 data bits are transmitted LSB first,
MSB last. A weak pullup resistor can be used to maintain
logic 1 on the DIO pin while the MAX1455 is in digital
mode. This is to prevent unintended 1 to 0 transitions on
this pin, which would be interpreted as a communication
start bit. Communications are only allowed when the
Secure-Lock byte is disabled (i.e., CL[7:0] = 00HEX ) or
UNLOCK is held high. Table 8 is the control location.
The first Command Byte sent to the MAX1455 after
power-up, or following receipt of the reinitialization
command, is used by the MAX1455 to learn the com-
munication baud rate. The initialization sequence is a 1-
byte transmission of 01 hex, as follows:
The start bit, shown in bold above, initiates the baud rate
synchronization. The 8 data bits 01hex (LSB first) follow
this and then the stop bit, also shown in bold above. The
MAX1455 uses this sequence to calculate the time inter-
val for a 1-bit transmission as a multiple of the period of
its internal oscillator. The resulting number of oscillator
clock cycles is then stored internally as an 8-bit number
(BITCLK). Note that the device power supply should be
stable for a minimum period of 1ms before the initializa-
tion sequence is sent. This allows time for the POR func-
tion to complete and DIO to be configured by the
Secure-Lock byte or UNLOCK.
1 1 1 1 1 0 1 0 0 0 0 0 0 0 1 1 1 1 1 1
Communication Protocol
Initialization Sequence
MAX1455 Digital Mode
Conditioner
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