Datasheet MAX6627 (Maxim) - 7

link to page 7 link to page 7 MAX6627/MAX6628 Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface tCSS CS SCK tDV tDO tTR SDO D15 D3 D2 D1 D0 Figure 2. SPI Timing Diagram
Table 2. Temperature Data Format
in Table 3. The MAX6627/MAX6628 can also directly measure the die temperature of CPUs and other ICs with
(Two’s Complement)
on-board temperature-sensing diodes.
TEMPERATURE DIGITAL OUTPUT (BINARY)
The transistor must be a small-signal type with a
(°C) D15–D3 D2 D1, D0
rela-tively high forward voltage. This ensures that the 150 0,1001,0110,0000 0 XX input voltage is within the A/D input voltage range. The 125 0,0111,1101,0000 0 XX forward voltage must be greater than 0.25V at 10µA at the highest expected temperature. The forward voltage 25 0,0001,1001,0000 0 XX must be less than 0.95V at 100µA at the lowest expected 0.0625 0,0000,0000,0001 0 XX temperature. The base resistance has to be less than 0 0,0000,0000,0000 0 XX 100Ω. Tight specification of forward-current gain (+50 to +150, for example) indicates that the manufacturer -0.0625 1,1111,1111,1111 0 XX has good process control and that the devices have -25 1,1110,0111,0000 0 XX consistent characteristics. -55 1,1100,1001,0000 0 XX
ADC Noise Filtering
0°C. When power is first applied and VCC rises above The integrating ADC has inherently good noise 1.6V (typ), the device starts to convert, although temperature rejection, especially of low-frequency signals such as reading is not recommended at VCC levels below 3.0V. 60Hz/120Hz power-supply hum. Micropower operation places constraints on high-frequency noise rejection. Lay
Serial Interface
out the PCB carefully with proper external noise filtering Figure 2 is the serial interface timing diagram. The data for high-accuracy remote measurements in electrically is latched into the shift register on the falling-edge of noisy environments. the CS signal and then clocked out at the SDO pin on the falling-edge of SCK with the most-significant bit
Table 3. SOT23-Type Remote-Sensor
(MSB) first. There are 16 edges of data per frame. The
Transistor Manufacturers
last 2 bits, D0 and D1, are always in high-impedance mode. The falling-edge of CS stops any conversion in
MANUFACTURER MODEL
progress, and the rising-edge of CS always starts a new Central Semiconductor (USA) CMPT3904 conversion and resets the interface. It is required to maintain Motorola (USA) MMBT3904 a 320ms minimum pulse width of high CS signal before a conversion starts. Rohm Semiconductor (Japan) SST3904 Siemens (Germany) SMBT3904
Applications Information
Zetex (England) FMMT3904CT-ND
Remote-Diode Selection Note:
Transistors must be diode connected (Short the Base to Temperature accuracy depends upon having a good- the Collector). quality, diode-connected, small-signal transistor. Accuracy has been experimentally verified for all of the devices listed www.maximintegrated.com Maxim Integrated │ 7