AD5933 datasheet(24/40 Pages) AD

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AD5933

Data Sheet

Rev. E | Page 24 of 40

Table 11. Control Register Map (D11, D8 to D0)

Bits

Description

D11

No operation

PGA gain; 0 = ×5, 1 = ×1

Reserved; set to 0

Reset

External system clock; set to 1

Internal system clock; set to 0

Reserved; set to 0

Control Register Decode

Initialize with Start Frequency

This command enables the DDS to output the programmed

start frequency for an indefinite time. It is used to excite the

unknown impedance initially. When the output unknown

impedance has settled after a time determined by the user, the

user must initiate a start frequency sweep command to begin

the frequency sweep.

Start Frequency Sweep

In this mode the ADC starts measuring after the programmed

number of settling time cycles has elapsed. The user has the

ability to program an integer number of output frequency cycles

(settling time cycles) to Register Address 0x8A and Register

Address 0x8B before the commencement of the measurement

at each frequency point (see Figure 28).

Increment Frequency

The increment frequency command is used to step to the next

frequency point in the sweep. This usually happens after data

from the previous step has been transferred and verified by the

DSP. When the AD5933 receives this command, it waits for the

programmed number of settling time cycles before beginning

the ADC conversion process.

Repeat Frequency

The AD5933 has the facility to repeat the current frequency

point measurement by issuing a repeat frequency command to

the control register. This has the benefit of allowing the user to

average successive readings.

Measure Temperature

The measure temperature command initiates a temperature

reading from the part. The part does not need to be in power-

up mode to perform a temperature reading. The block powers

itself up, takes the reading, and then powers down again. The

temperature reading is stored in a 14-bit, twos complement

format at Register Address 0x92 and Register Address 0x93.

Power-Down Mode

The default state on power-up of the AD5933 is power-down

mode. The control register contains the code 1010,0000,0000,0000

(0xA000). In this mode, both the VOUT and VIN pins are

connected internally to GND.

Standby Mode

This mode powers up the part for general operation; in standby

mode the VIN and VOUT pins are internally connected to ground.

Output Voltage Range

The output voltage range allows the user to program the

excitation voltage range at VOUT.

PGA Gain

The PGA gain allows the user to amplify the response signal

into the ADC by a multiplication factor of ×5 or ×1.

Reset

A reset command allows the user to interrupt a sweep. The start

frequency, number of increments, and frequency increment

frequency command is required to restart the frequency sweep

command sequence.

START FREQUENCY REGISTER (REGISTER

ADDRESS 0x82, REGISTER ADDRESS 0x83,

The default value of the start frequency register upon reset is

as follows: D23 to D0 are not reset on power-up. After a reset

command, the contents of this register are not reset.

The start frequency register contains the 24-bit digital represen-

tation of the frequency from where the subsequent frequency

sweep is initiated. For example, if the user requires the sweep to

start from frequency 30 kHz (using a 16.0 MHz clock), then the

user programs the value of 0x0F to Register Address 0x82, the

value of 0x5C to Register Address 0x83, and the value of 0x28 to

at 30 kHz.

The code to be programmed to the start frequency register is

MHz

kHz

27 ≡





























Code

Frequency

Start

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