feature

10-bit temperature-to-digital converter; –35°C to +85°C operating temperature range; 2C precision SPI 174 ; and DSP-compatible serial interface; shutdown mode; space-saving MSOP package.

application

Hard Disk Drives; Personal Computers; Electronic Test Equipment; Office Equipment; Home Appliances; Process Control; Mobile Phones.

General Instructions

The AD7314 is a complete temperature monitoring system in an 8-lead MSOP package. It contains a bandgap temperature sensor and 10-bit ADC for monitoring and digitizing temperature readings with a resolution of 0.25∞C. There is a flexible serial interface that can be easily connected to most microcontrollers. The interface is compatible with SPI, QSPI™ and MICROWIRE™ protocols and is also dsp compatible. The part has a standby mode controlled via the serial interface.

The low supply current and SPI-compatible interface of the AD7314 make it ideal for a variety of applications, including personal computers, office equipment, and home appliances.

Product Highlights

1. AD7314 has a chip temperature sensor, which can accurately measure the ambient temperature. The measurement temperature range is -35∞C to +85∞C, and the temperature accuracy is ±2∞C.

2. The supply voltage is 2.65 V to 5.5 V.

3. Space-saving 8-lead MSOP package.

4. The 10-bit temperature reading is 0.25∞C resolution.

5. AD7314 adopts standby mode, which reduces the current consumption to a maximum of 1 mA.

Timing Characteristics (TA = TMIN to TMAX, VDD = 2.65 V to 5.5 V, see Figure 1 unless otherwise noted.)

notes

1. Guaranteed by design and features, no production testing.

2. All input signals are specified with tr=tf=5ns (10% to 90% of V DD) and timed from a voltage level of 1.6v All specifications apply to -35∞C to + unless otherwise noted 85∞C is measured with the load circuit of Figure 2.

Absolute Maximum Ratings1 VDD to GND. . –0.3V to +7V

Digital Input Voltage Ground. . . . . . –0.3V to VDD+0.3V

Digital output voltage to ground . . . . –0.3V to VDD+0.3V

Operating Temperature Range . . . . . . . . . . –35°C to +85°C

Storage temperature range. . . . . . . . . .–65°C to +150°C

Junction Temperature . . . . . . . . . . . . . . . . . . . . 150°C

MSOP package, power consumption . . . . . . . . . . . . 450 MW

θJA Thermal Impedance . . . . . . . . . . . . . . . 206 °C/W

Lead temperature, solder vapor phase (60 seconds) . . . . . . . . . . . . 215°C

Infrared (15 seconds) . . . . . . . . . . . . . . 220°C

Lock ID Pin2. . . . . . . . . . . . . .. ≤ –70 mA

Lock all other pins . . . . . . . . . . . . ≥ –110 mA

notes

1. Stresses listed above absolute maximum ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device under the above conditions or any other section of this specification does not imply that exposure to Absolute Maximum Ratings for extended periods of time may affect device reliability.

2. Proper use of the ID pin will prevent any latch-up from happening In an application, the ID pin should be connected to VDD through a 100 kΩ resistor or left open circuit If the application conforms to this recommendation, the ID pin will never be seen – 70 mA.

circuit information

The AD7314 is a 10-bit digital temperature sensor. This part contains an on-chip temperature sensor, a 10-bit A/D converter, and reference and serial interface logic functions in the MSOP package. The A/D converter part consists of traditional successive approximation around a capacitor DAC Converter composition. These parts are capable of operating from 2.65 V to 5.5 V supplies. An on-chip temperature sensor allows accurate measurement of ambient device temperature. The AD7314 operates over a measurement range of -35∞C to +85∞C.

Converter Details

The conversion clock for this part is internally generated, so no external clock is required, except when reading from and writing to the serial port. In normal mode, the internal clock oscillator runs an automatic conversion sequence to initiate conversions every 400 ms. At this point, the part wakes up and performs a temperature conversion. This temperature conversion usually takes 25 milliseconds, at which time the part automatically shuts down. The latest temperature conversion results are available in the serial output register at any time. The AD7314 can be put into shutdown mode through the control register, where In this case, the on-chip oscillator is turned off and no further conversions are initiated until the AD7314 exits shutdown mode. Even in shutdown mode, the result of the last conversion before shutdown can be read from the AD7314.

In auto-conversion mode, the results of the internal clock oscillator restarting the conversion at the end of the read or write operation are available each time a read or write operation is performed, usually after 25 ms. Similarly, when the part comes out of shutdown mode, the internal The clock oscillator is restarted and the conversion results are available, typically reading the device again after 25 ms before the conversion is complete will provide the same data set.

Temperature value register

The temperature value register is a read-only register, which stores the temperature and temperature data read from the ADC in 10-bit two's complement format as shown in Table 1. This shows the full theoretical range of the ADC from -128∞C to +127∞C, but in practice the temperature measurement range is limited to the device's operating temperature range (–35∞C to +85∞C).

serial interface

The serial interface on the AD7314 consists of four wires: CE, SCLK, SDI, and SDO The interface can operate in three-wire mode, SDI is grounded, in this case, the interface is read-only, reading data from the data register through the SDO line If required, the SDI line is used to write the part into standby mode. When multiple devices are connected to the serial clock and data lines, the CE line is used to select the device. To ensure that the serial port is properly reset after power-up, the CE must be The serial clock is only active when CE is high when the serial port is at a logic low level prior to the first access to the serial port. For proper data synchronization, CE must be low when the serial port is not being accessed. The part operates in slave mode and requires an externally applied serial clock to the SCLK input to access the data in the data registers The serial interface on the AD7314 is designed to allow the part to connect to systems that provide a serial interface with serial data Synchronized clocks such as 80C51, 87C51, 68HC11 , 68HC05 and PIC16Cxx microcontrollers and DSP processors.

A read operation of the AD7314 accesses data from the temperature value register, while a write operation to the part writes data into the control register until the rising edge of the 15th SCLK cycle, when the input data is not loaded into the control register on the rising edge of the serial clock. When data is updated on the SDO line, the data on the SDI line is latched on the falling edge of the serial clock.

read operation

Figure 3 shows the interface diagram for a serial read from the AD7314. The CE line enables the SCLK input to transmit leading zero bits and 10 bits of data during the read operation. The read operation occurs during a stream of 16 clock pulses. The output data is on the rising edge of SCLK. Update If 10-bit data is being read, serial data is accessed in bytes. At the end of the read operation, the SDO line remains in the state of the last bit of data clocked out of the AD7314 until CE returns low, at which point the SDO line enters three states.

write operation

Figure 3 also shows the interface diagram for a serial write to the AD7314. The write operation occurs at the same time as the read operation. Data is recorded to the control register on the falling edge of SCLK. Only the third bit in the data flow provides the function of user control. The third bit is The power down bit, when set to 1, puts the AD7314 in shutdown mode The first two bits of the data stream are unimportant, and all other bits in the data stream except the power down should be 0 to ensure proper operation of the AD7314 data is loaded The data in the control register to the 15th rising SCLK edge is valid at this time, that is, if the part is programmed into a shutdown state, it is valid at this time. If CE is lowered before the 15th SCLK edge, the control register will not be loaded and the part will be turned off. The electrical state also does not change.

Microcontroller Interface

The AD7314 serial interface allows simple interfacing with most microcontrollers and microprocessors. A typical interface circuit is shown in Figure 4.

If the ID pin of the AD7314 is used as a replacement temperature sensor, it can be used to differentiate the device. Connected to pin 7 (ID pin) is a 1 kW internal pull-down resistor If a pull-up resistor is used on pin 7 to help To identify the device, a pull-up value with a rated voltage of 2.9 V and a VDD of 100 kW is recommended. Figure 5 shows the recommended pull-up resistor value for the ID pin. , thereby reducing any negative impact on the temperature sensor measurement.

Install the AD7314

The AD7314 can be used in surface or air temperature sensing applications. If the device is bonded to the surface with thermally conductive adhesive, the die temperature will be around 0.1∞C of the surface temperature due to the low power dissipation of the device. If the ambient air temperature is different from the measured surface temperature, then Care should be taken to insulate the back and leads of the device from air. The ground pins provide the best thermal path to the die, so the temperature of the die will be close to that of the printed circuit ground track. Care should be taken to ensure that it has good thermal contact with the surface being tested. As with any integrated circuit, the AD7314 and its associated wiring and circuitry must be protected from moisture to prevent leakage and corrosion, especially in cold conditions where condensation is more likely. Waterproof varnishes and conformal coatings can be used to protect the small AD7314 package Allows it to be installed inside a sealed metal probe, providing a safe environment for the device.

Power decoupling

The AD7314 should be separated from at least a 0.1 mF ceramic capacitor between VDD and GND. This is especially important if the AD7314 is mounted away from the power supplies.

Typical Temperature Error Graph

Figure 6 shows a typical temperature error plot for a device with a VDD of 2.65 V.