Datasheet

0°C. When power is first applied and V
CC
rises above
1.6V (typ), the device starts to convert, although tempera-
ture reading is not recommended at V
CC
levels below
3.0V.
Serial Interface
Figure 2 is the serial interface timing diagram. The data
is latched into the shift register on the falling edge of the
CS signal and then clocked out at the SDO pin on the fall-
ing edge of SCK with the most-significant bit (MSB) first.
There are 16 edges of data per frame. The last 2 bits, D0
and D1, are always in high-impedance mode. The falling
edge of CS stops any conversion in progress, and the ris-
ing edge of CS always starts a new conversion and resets
the interface. It is required to maintain a 320ms minimum
pulse width of high CS signal before a conversion starts.
Applications Information
Remote-Diode Selection
Temperature accuracy depends upon having a good-
quality, diode-connected, small-signal transistor.
Accuracy has been experimentally verified for all of the
devices listed in Table 3. The MAX6627/MAX6628 can
also directly measure the die temperature of CPUs and
other ICs with on-board temperature-sensing diodes.
The transistor must be a small-signal type with a rela-
tively high forward voltage. This ensures that the input
voltage is within the A/D input voltage range. The for-
ward voltage must be greater than 0.25V at 10µA at
the highest expected temperature. The forward voltage
must be less than 0.95V at 100µA at the lowest expect-
ed temperature. The base resistance has to be less
than 100Ω. Tight specification of forward-current gain
(+50 to +150, for example) indicates that the manufac-
turer has good process control and that the devices
have consistent characteristics.
ADC Noise Filtering
The integrating ADC has inherently good noise rejec-
tion, especially of low-frequency signals such as
60Hz/120Hz power-supply hum. Micropower operation
places constraints on high-frequency noise rejection.
Lay out the PCB carefully with proper external noise fil-
tering for high-accuracy remote measurements in elec-
trically noisy environments.
Table 3. SOT23-Type Remote-Sensor
Transistor Manufacturers
Table 2. Temperature Data Format
(Two’s Complement)
Figure 2. SPI Timing Diagram
MANUFACTURER MODEL
Central Semiconductor (USA) CMPT3904
Motorola (USA) MMBT3904
Rohm Semiconductor (Japan) SST3904
Siemens (Germany) SMBT3904
Zetex (England) FMMT3904CT-ND
TEMPERATURE
(°C)
DIGITAL OUTPUT (BINARY)
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
D15 D0D1D2D3
SCK
SDO
t
DV
t
CSS
t
DO
CS
t
TR
MAX6627/MAX6628 Remote ±1ºC Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface
www.maximintegrated.com
Maxim Integrated │ 6
Note: Transistors must be diode connected (short the base to
the collector).