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AD5933

Data Sheet

Rev. E | Page 16 of 40

SYSTEM CLOCK

The system clock for the AD5933 can be provided in one of two

ways. The user can provide a highly accurate and stable system

clock at the external clock pin (MCLK). Alternatively, the AD5933

provides an internal clock with a typical frequency of 16.776 MHz

by means of an on-chip oscillator.

The user can select the preferred system clock by programming

Bit D3 in the control register (Register Address 0x81, see

Table 11). The default clock option on power-up is selected to

be the internal oscillator.

The frequency distribution of the internal clock with temperature

can be seen in Figure 14, Figure 15, and Figure 16.

TEMPERATURE SENSOR

The temperature sensor is a 13-bit digital temperature sensor with

a 14th bit that acts as a sign bit. The on-chip temperature sensor

allows an accurate measurement of the ambient device temper-

ature to be made.

The measurement range of the sensor is −40°C to +125°C. At

+150°C, the structural integrity of the device starts to deteriorate

when operated at voltage and temperature maximum specifica-

tions. The accuracy within the measurement range is ±2°C.

TEMPERATURE CONVERSION DETAILS

The conversion clock for the part is internally generated; no

external clock is required except when reading from and writing

to the serial port. In normal mode, an internal clock oscillator

runs an automatic conversion sequence.

The temperature sensor block defaults to a power-down state.

To perform a measurement, a measure temperature command

is issued by the user to the control register (Register Address 0x80

and Register Address 0x81). After the temperature operation is

complete (typically 800 μs later), the block automatically

powers down until the next temperature command is issued.

The user can poll the status register (Register Address 0x8F) to see

if a valid temperature conversion has taken place, indicating that

valid temperature data is available to read at Register Address

0x92 and Register Address 0x93 (see the Register Map section).

TEMPERATURE VALUE REGISTER

The temperature value register is a 16-bit, read-only register that

stores the temperature reading from the ADC in 14-bit, twos

complement format. The two MSB bits are don’t cares. D13 is the

sign bit. The internal temperature sensor is guaranteed to a low

value limit of –40°C and a high value limit of +150°C. The digital

output stored in Register Address 0x92 and Register Address 0x93

for the various temperatures is outlined in Table 6. The tempera-

ture sensor transfer characteristic is shown in Figure 21.

Table 6. Temperature Data Format

Temperature

Digital Output D13…D0

−40°C

11, 1011, 0000, 0000

−30°C

11, 1100, 0100, 0000

−25°C

11, 1100, 1110, 0000

−10°C

11, 1110, 1100, 0000

−0.03125°C

11, 1111, 1111, 1111

0°C

00, 0000, 0000, 0000

+0.03125°C

00, 0000, 0000, 0001

+10°C

00, 0001, 0100, 0000

+25°C

00, 0011, 0010, 0000

+50°C

00, 0110, 0100, 0000

+75°C

00, 1001, 0110, 0000

+100°C

00, 1100, 1000, 0000

+125°C

00, 1111, 1010, 0000

+150°C

01, 0010, 1100, 0000

TEMPERATURE CONVERSION FORMULA

Positive Temperature = ADC Code (D)/32

Negative Temperature = (ADC Code (D) – 16384)/32

where ADC Code uses all 14 bits of the data byte, including the

sign bit.

Negative Temperature = (ADC Code (D) – 8192)/32

where ADC Code (D) is D13, the sign bit, and is removed from the

ADC code.)

–40°C

–0.03125°C

–30°C

11, 1111, 1111, 1111

11, 1100, 0100, 0000

11, 1011, 0000, 0000

TEMPERATURE (°C)

75°C

150°C

01, 0010, 1100, 0000

00, 1001, 0110, 0000

00, 0000, 0000, 0001

Figure 21. Temperature Sensor Transfer Function

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