12-Bit Serial-Output Temperature Sensors

with 5-Channel ADC

14

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Input Data Format

Input data (configuration and conversion bytes) are

clocked into the MAX1298/MAX1299 at DIN on the ris-

ing edge of SCLK when CS is low. The start bit (MSB)

of an input data byte is the first logic 1 bit that arrives:

After CS falls,

OR

after receipt of a complete configuration byte with no

conversion in progress,

OR

after 16 bits have been clocked onto DOUT following a

conversion.

Output Data Format

Output data from the MAX1298/MAX1299 are clocked

onto DOUT on the falling edge of SCLK in the form of two

8-bit words, MSB first (Table 1). For temperature conver-

sions, the output is 12-bit binary (D10–S0) padded with 2

leading extraneous bits and two trailing zeros. For volt-

age conversions, the output is 12-bit two’s-complement

binary (D11–D0) with 1 sub-bit and two trailing zeros.

Figure 5 shows the bipolar transfer function.

Performing a Conversion

On power-up, the MAX1298/MAX1299 defaults to shut-

down mode. Start a conversion by transferring a configu-

ration byte and a conversion byte into DIN with the

control formats shown in Tables 2 and 3, respectively.

(See

Power Modes for related discussion.)

SSTRB goes low on the falling edge of the last bit of the

conversion byte, and it returns high when the conversion

is complete. For best noise performance, SCLK should

remain low while SSTRB is low. Typical conversion times

are 2.2ms for temperature measurements and 1.1ms for

voltage measurements. The MSB of the 2 output bytes is

present at DOUT starting at the rising edge of SSTRB.

Successive SCLK falling edges shift the two 8-bit data

bytes out from an internal register. Additional (>16)

SCLK edges will result in zeros on DOUT.

SSTRB does not go into a high-impedance state when CS

goes high. Pulling CS high prevents data from being

clocked in or out, but it does not adversely affect a con-

version in progress. Figure 6 shows SSTRB timing details.

Subsequent conversions with the same reference mode

do not require a configuration byte.

Reference Selection

Select between internal and external voltage modes

through bit REF of the configuration byte. Set REF = 1

for internal reference mode and REF = 0 for external

reference mode.

DOUT

DIN

SCLK

CS

VALID

VALID

VALID

X

X

X

Figure 4. Detailed Serial Interface Timing

011111111111

011111111110

000000000010

000000000001

000000000000

111111111111

111111111110

111111111101

100000000010

100000000001

OUTPUT CODE

1LSB =

2048

0

+ FS - 1LSB

- FS + 1LSB

IN+ - IN - (LSB)

Figure 5. Bipolar Transfer Function