12-Bit + Sign Digital Temperature Sensors

with Serial Interface

6

_______________________________________________________________________________________

finish. CS’s falling edge stops any conversion in

progress, and data is latched into the shift register.

Then the data clocks out at SO on SCK’s falling edge

with the sign bit (D15) first, followed by the MSB. Data

is sent in one 16-bit word, and CS must remain low until

all 16 bits are transferred. If CS goes high in the middle

of a transmission, it is necessary to wait the conversion

time (less than 300ms) before attempting a new read.

The serial data is composed of 12 + 1 data bits

(D15–D3) and 3 trailing bits (D2–D0). D2 is always low,

serving as the confirmation bit that the device has been

communicated with. The last 2 bits, D0 and D1, are

undefined and are always in high-impedance mode

(Table 1). The power-up state for SO is high imped-

ance. Figure 3 shows the detailed serial timing specifi-

cations for the SPI port. The temperature data format is

in two's complement format (Table 2).

Power Shutdown Mode

The MAX6629–MAX6632 do not have a built-in power

software shutdown mode. However, a power shutdown

mode is easily implemented utilizing an unused logic

gate. A typical CMOS or TTL logic output has enough

drive capability to serve as the power source if its out-

put voltage level exceeds 3V, as shown in Figure 1.

Drive the logic output low to provide a hardware shut-

down mode.

Idle Mode

The MAX6629–MAX6632 can be put into idle mode by

pulling CS low. Data can be clocked out when the

device is in idle mode.

Power-On Reset (POR)

The POR supply voltage of the MAX6629–MAX6632 is

typically 1.6V. Below this supply voltage, the interface

is inactive and the data register is set to the POR state,

0°C.

(typ), the device starts to convert, although temperature

Figure 3. SPI Timing Diagram

D15

D0

D1

D2

D3

SCK

SO

CS

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

Sign

MSB

Data

LSB

Data

Low

High-Z

High-Z

Table 1. Data Output Format

Table 2. Temperature Data Format

(Two’s Complement)

DIGITAL OUTPUT (BINARY)

TEMPERATURE

(°C)

D15–D3

D2

D1, D0

150

0,1001,0110,0000

0

XX

125

0,0111,1101,0000

0

XX

25

0,0001,1001,0000

0

XX

0.0625

0,0000,0000,0001

0

XX

0

0,0000,0000,0000

0

XX

-0.0625

1,1111,1111,1111

0

XX

-25

1,1110,0111,0000

0

XX

-55

1,1100,1001,0000

0

XX