 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
AD5932 Datasheet(PDF) 18 Page - Analog Devices |
|
||||||||||||||||||||||||||||||
AD5932 Datasheet(HTML) 18 Page - Analog Devices |
|
|
18 / 28 page 
AD5932 Data Sheet Rev. C | Page 18 of 28 Therefore, in this example, a time interval of 20 ns × 2047 = 40 µs is the maximum, with the minimum being 40 ns. For some applications, this maximum time of 40 µs may be insufficient. Therefore, to allow for sweeps that need a longer increment interval, time-base multipliers are provided. D12 and D11 are dedicated to the time-base multipliers, as shown in the bit map above. A more detailed table of the multiplier options is given in Table 9. Table 9. Time-Base Multiplier Values D12 D11 Multiplier Value 0 0 Multiply (1/MCLK) by 1 0 1 Multiply (1/MCLK) by 5 1 0 Multiply (1/MCLK) by 100 1 1 Multiply (1/MCLK) by 500 If MCLK = 50 MHz and a multiplier of 500 is used, then the base interval (TBASE) is now (1/(50 MHz) x 500)) = 10 µs. Using a multiplier of 500, the maximum increment interval is 10 µs × 211− 1= 20.5 ms. Therefore, the option of time-base multipliers gives the user enhanced flexibility when programming the length of the frequency window, because any frequency can be output for a minimum of 40 ns up to a maximum of 20.5 ms. The above example shows a fixed number of clock periods. Note that the same equally applies to fixed numbers of clock cycles. Length of Scan Time The length of time to complete a user-programmed frequency scan is given by the following equation: TSCAN = (1 + NINCR) × TBASE ACTIVATING AND CONTROLLING THE SCAN After the registers have been programmed, a 0 to 1 transition on the CTRL pin starts the scan. The scan always starts from the frequency programmed into the FSTART register. It changes by the value in the ∆f register and increases by the number of steps in the NINCR register. However, the time interval of each frequency can be internally controlled using the tINT register or externally controlled using the CTRL pin. The available options are • Auto-increment • External increment Auto-Increment Control The value in the tINT register is used to control the scan. The AD5932 outputs each frequency for the length of time pro- grammed in the TINT register, before moving on to the next frequency. To set up the AD5932 to this mode, INT/EXT INCR (Bit D5) must be set to 0. External Increment Control In this case, the time interval, tINT, is set by the pulse rate on the CTRL pin. The first 0 to 1 transition on the pin starts the scan. Each subsequent 0 to 1 transition on the CTRL pin increments the output frequency by the value programmed into the ∆f register. To set up the AD5932 to this mode, INT/EXT INCR (Bit D5) must be set to 1. INTERRUPT Pin This function is used as an interrupt during a frequency scan. A low-to-high transition on this pin is sampled by the internal MCLK, thereby resetting internal state machines, which results in the output going to midscale. STANDBY Pin Sections of the AD5932 that are not in use can be powered down to minimize power consumption. This is done by using the STANDBY pin. For optimum power savings, it is recom- mended to reset the AD5932 before entering standby. Doing so reduces the power-down current to 20 μA. When this pin is high, the internal MCLK is disabled, and the reference, DAC, and regulator are powered down. When in this state, the DAC output of the AD5932 remains at its present value, because the NCO is no longer accumulating. When the device is taken back out of standby mode, the MCLK is re- activated, and the scan continues. To ensure correct operation for new data, it is recommended that the device be internally reset, using a control register write or using the INTERRUPT pin, and then restarted. |
|
English ▼
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
