MAX1462 Datasheet, PDF(11/16 Page) Maxim Integrated Products – Low-Voltage, Low-Power, 16-Bit Smart ADC

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MAX1462 Datasheet, PDF (11/16 Pages) Maxim Integrated Products – Low-Voltage, Low-Power, 16-Bit Smart ADC

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Low-Voltage, Low-Power,

16-Bit Smart ADC

Table 6. Configuration Register Bitmap

EEPROM

ADDRESS

(HEX)

BIT

POSITION

DESCRIPTION

0 (LSB) CO-0 (LSB)

CO-1 (MSB)

CO-S (Sign)

PGA-1 (MSB)

PGA-0 (LSB)

Maxim Reserved

Op Amp Power-Down

Maxim Reserved

TSO-0 (LSB)

TSO-1

TSO-2 (MSB)

Maxim Reserved

15 (MSB) Repeat Mode

3) Issue command 0 hex.

The value of VDD should be lowered to its normal operat-

ing values (2.4V to 3.6V) after the EEPROM program-

ming sequence is completed.

Test System Interface:

Observing the DSP Operation

Test system commands 8 hex and A hex initiate a con-

version while allowing the test system to observe the

operation of the DSP. To calibrate a unit, the test sys-

tem must know the digitized temperature and sensor

signals, stored in DSP registers 8 and 9, and the cali-

brated and compensated output stored in DSP register

10. The test system should also verify the EEPROM con-

tents, registers 0â7. All these signals pass through DSP

microcode. The SDO pin outputs the S register values,

and the SDIO pin tells the tester which signal is currently

on S.

There are three internal DSP registers that are directly

observable on the SDIO and SDO pins:

â¢ S: 16-bit DSP Scratch or Accumulator register, con-

taining the result of the execution of the current

microcode instruction.

â¢ P: 8-bit DSP Program Pointer register, which holds

the address of the instruction ROM microcode.

â¢ PS: 8-bit DSP Program Store register. PS is the

instruction that the DSP is currently executing. PS is

the instruction ROM data at address P.

The DSP instructions relevant to the test system are list-

ed in Table 8.

After the test system sends the Start Conversion com-

mands 8 hex or A hex, SDIO and SDO are both

enabled as MAX1462 serial outputs. The test system

should disable (high impedance) its SDIO driver to

avoid a bus conflict at this time so that the MAX1462

can drive the pin. After the DSP executes each one of

the microcode instructions, the contents of the S, P,

and PS registers are output in a serial format (Figure 4).

A new DSP instruction and a new state of the S, P, and

PS registers are delivered every 16n + 9 clock cycles,

where n = 0, 1, 2... after the Start Conversion command

completes. The tester should latch the SDIO and SDO

bits on the falling edge of the XIN clock signal. When

the P and PS registers in Table 8 appear on SDIO, the

tester should save the corresponding SDO data.

The conversion timing of the MAX1462 is shown in

Figure 5 and Table 9. In the figure, the conversion is ini-

tiated by a rising transition on the START pin.

Equivalently, conversion can be initiated in TEST mode

after completion of tester commands 8 hex or A hex, or

reinitiated by the state of the Repeat Mode bit in the

configuration register. After a conversion is initiated, the

16-bit ADC digitizes the temperature and sensor sig-

nals during tADC. Then, the DSP executes the instruc-

tion ROM microcode during tDSP. In TEST mode, and

during tDSP, SDIO and SDO outputs carry useful infor-

mation. At 130,586 clock cycles after the Start

Conversion command is received, the LSB of the S and

P DSP registers is available on SDO and SDIO. The last

DSP instruction is D0 hex. The tester can now start a

new communication sequence by lowering RESET for

at least 16 clock cycles, and then resume driving SDIO.

SDIO becomes high impedance when RESET is low.

Applications Information

Calibration and Compensation Procedure

Perform fine calibration by characterizing the sensor/

MAX1462 pair using the test system and then finding

the calibration coefficients Gain, G1, G2, Of0, Of1, and

Of2 using the equations below. This simple fine-calibra-

tion procedure requires three temperatures, denoted A,

B, and C, and two sensor excitations, named S and L for

small and large. Thus, there are six data points (AS, AL,

BS, BL, CS, and CL); six unknown calibration coeffi-

cients; and six versions of the characteristic equation, in

the form:

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